A direct result of herbicide resistance development to more than one mode of action is the necessity of using combinations of different modes of action to combat weeds in rice systems. Permanently-flooded rice agroecosystems are limited to few available herbicides in California, largely due to ecotoxicity and strict regulatory structure . As of 2019, there are 13 registered active ingredients for water-seeded rice in California and 9 modes of action registered for use . The rise in herbicide resistance has increased the cost and difficulty of weed management, necessitating demand for novel herbicide development to delay resistance expansion and assist the management of current herbicide-resistant weed biotypes . The following studies examined the crop response to chemicals not currently in use in California water-seeded rice. CHAPTER ONE describes field studies performed in 2019 and 2021 at the Rice Experiment Station in Biggs, CA. The efficacy of pyraclonil, a protox inhibitor, was explored alone and in combination with several currently available rice herbicides against common grass, sedge, and broadleaf weeds in California rice field. Combination treatments included pyraclonil at 0.3 kg ai ha-1 applied the day of seeding, in combination with or followed by recommended rates of propanil, clomazone, benzobicyclon plus halosulfuron, thiobencarb, bispyribac-sodium, penoxsulam, or florpyrauxifen-benzyl at their respective recommended application timings. Rice phytotoxicity and yield in response to pyraclonil and these registered herbicides was evaluated. Pyraclonil applied alone had mixed effects on weed control, but all pyraclonil herbicide combination treatments controlled watergrass species, bearded sprangletop, ricefield bulrush, smallflower umbrellas edge, ducksalad, and redstem consistently better than pyraclonil applied alone.

Pyraclonil applied alone caused minor visible rice injury that varied by year but did not reduce yields. This study determined that pyraclonil was effective as a base treatment herbicide and may prove to be a new useful tool for rice growers to incorporate into their weed management programs.CHAPTER TWO details greenhouse studies undertaken in 2021-2022 to evaluate the response of several rice genotypes to five different rates of foliar-applied metribuzin, a Photosystem II inhibitor herbicide not currently used in California rice systems. Short-grain rice cultivars as a group were found to be more susceptible to crop phytotoxicity than the long-grain or medium-grain rice lines. Crop injury from metribuzin was correlated with biomass reductions and plant height reductions . The results indicate that further research is needed to establish metribuzin’s candidacy for development as a POST emergence product in rice. This exploration of novel herbicides has characterized the activity of pyraclonil in California rice, both alone and in combination with other water-seeded rice herbicides. The efficacy of the herbicide, as well as the response of the target crop, has been identified and establishes pyraclonil as an herbicide with great potential for integration into existing rice weed management programs. The differential responses of various rice cultivars to increasing doses of foliar metribuzin has described heretofore unknown rice responses and identified areas of concentration upon which future researchers may focus. Introduction of novel herbicides and continued analysis of their activity in rice allows for development of alternate methods of sustainable weed control to contend with the rise of herbicide resistance amid the common weeds of California rice agriculture.Rice is the major calorie source for a large proportion of the world’s population and is one of the most commonly grown agricultural commodities in the world . California is the second largest rice-growing state in the USA, with approximately 200,000 ha of rice, most of which is concentrated in the Sacramento Valley. The majority of rice in California is produced using a continuously flooded, i.e., water-seeded system, where rice is pre-germinated and aerially seeded into fields with a 10-to 15 cm existing flood . The flooded conditions in which California rice is grown favor flood-adapted, competitive grass weeds such as watergrass species Beauv. spp.and bearded sprangletop [Leptochloa fusca Kunth ssp. fascicularis N. Snow] . The continuously flooded system also promotes sedges such as rice field bulrush [Schoenoplectus mucronatus Palla] and small flower umbrellas edge as well as aquatic broadleaf weeds such as ducksalad [Heteranthera limosa Willd.] and redstems . Weeds are the greatest biological constraint to rice yields, and farmer inputs towards weed management are expected to increase as herbicide resistance spreads worldwide . The potential yield lost to weed infestation is species dependent, and the practice of continuous rice monoculture in California has resulted in an abundance of highly competitive weeds that negatively impact rice yields . In California rice fields, weedy grasses are the largest predictors of overall yield loss . Late watergrass [Echinochloa phyllopogon . Koss] competition has caused rice yield losses as high as 59% . Studies in Arkansas have shown rice yield losses to be 79% from competition with barnyardgrass [Echinochloa crus-galli Beauv.] and 36% from bearded sprangletop competition . In the Midsouth region, yield losses due to ducksalad infestations can reach 30% . Most California rice herbicides are limited in the spectrum of weeds controlled and the length of residual activity, cannabis curing requiring herbicide treatment plans to consist of multiple herbicides to enact weed control over a range of weeds . Effective weed control in the state relies on combinations of herbicides to enact a complete spectrum of weed control Continuous use of herbicides with the same mode of action aids in the development of herbicide resistance in rice fields .

However, due to high costs of development and registration, few additional herbicides are currently available for California rice growers, particularly herbicides that target grass weeds . As of today, there are 13 registered active ingredients for water-seeded rice in California that belong to 9 modes of action . The rises in herbicide resistance have made weed management more difficult and more costly to California rice growers . Herbicide resistance has also been a major biological issue, with confirmed resistance from various populations of watergrass species and bearded sprangletop . California arrowhead and small flower umbrellas edge were the first confirmed cases of herbicide resistance in rice to bensulfuron-methyl, an ALS-inhibitor, in 1993 . Eight other rice weed species have since been identified with resistance to commonly used herbicides, some with resistance to more than one mode of action . A direct result of herbicide resistance development to more than one mode of action is the necessity of using combinations of different modes of action to combat weeds in rice systems. Pyraclonil is a broad-spectrum herbicide with protoporphyrinogen oxidase inhibitor mode of action that is new to California. Carfentrazone, which is a currently registered protox-inhibitor, is a viable herbicide for California water-seeded rice but lacks activity on grass weeds . Pyraclonil is presently in use in Japan and has shown efficacy against sulfonylurea-resistant broadleaf biotypes of Lindernia procumbens Borbas, grasses, and sedges . Currently, there is no record of protox inhibitor resistance in California rice weeds. Protox inhibition takes place inside the chloroplasts of plant cells. As the last enzyme in the common tetrapyrrole biosynthesis pathway prior to heme and chlorophyll synthesis, protoporphyrinogen IX oxidase catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX . Pyraclonil inhibits the conversion of protogen to proto by blocking protox activity. When protox is inhibited, excess protogen accumulates in the chloroplast until protogen leaks to cytoplasm . In cytoplasm, leaked protogen is oxidized into proto and is unable to reenter the chloroplast . When proto is exposed to light and molecular oxygen in the cytoplasm, it produces toxic oxygen species, which are responsible for lipid peroxidation and membrane disruption, resulting in overall plant death . A formulation of pyraclonil has been developed by Nichino America Inc. as a preemergent granular form that is suitable for aerial application in California water-seeded rice agroecosystems.Therefore, the objectives of this research were to determine the grass, sedge, and broadleaf control of pyraclonil alone and in partnership with other commonly used herbicides in water-seeded rice systems and determine the rice response to the granular formulation of pyraclonil.Field experiments were conducted during the 2019 and 2021 growing seasons at the Rice Experiment Station in Biggs, CA, USA . Soils at the study site are characterized as Esquon-Neerdobe silty clay with a pH of 5.1, and 2.8% organic matter. The study site weed seedbank has been previously described in Brim-DeForest et al. and contains watergrass species, bearded sprangletop, rice field bulrush, small flower umbrellas edge, ducksalad, and redstem.Seeds of medium-grain rice cultivar ‘M-206’ were soaked in water for 24 hours for pregermination and then drained and aerially seeded at a rate of 168 kg ha-1 into a 10 cm flooded field. Seeding dates were June 13, 2019, and June 1, 2021. Plots were 3 m by 6 m and surrounded by small levees to prevent herbicide cross contamination to other plots . Pyraclonil was applied as a granular formulation of 1.89% pyraclonil at a rate of 0.3 kg ai ha -1 at day of seeding . Pyraclonil was also applied in combination with propanil, clomazone, benzobicyclon plus halosulfuron, thiobencarb, bispyribac-sodium, penoxsulam, and florpyrauxifen-benzyl .Treatment applications were timed on rice emergence or development stages according to manufacturer labels. Granular herbicides were evenly broadcast by hand. Foliar applied herbicides were applied with a CO2-pressurized boom sprayer with a 2 m boom equipped with six 8003XR flat-fan nozzles calibrated to deliver 187 L ha-1 at 180 kPa. For the combination treatments including propanil, the spray mixture included 2.5% v/v crop oil concentrate . For the combination treatment including bispyribac-sodium, the spray mixture included a multifunction adjuvant of 0.37 ml ha-1 . Several of the contact herbicide treatments required the 10 cm permanent flood to be lowered in order to reveal the weeds. For the treatments containing propanil, bispyribac-sodium, and florpyrauxifen-benzyl, the plots were drained to reveal 70% of the weeds prior to that herbicide application and were reflooded to 10 cm 48 hours after application, according to the manufacturer labels.Visual ratings measuring weed control were conducted for watergrass species, bearded sprangletop, rice field bulrush, small flower umbrellas edge, ducksalad, and redstem at 14 and 42 DAT . Ratings consisted of a 0 to 100 scale, where 0 = no weed control, and 100 = no weeds present, or full control. Visual crop phytotoxicity ratings were conducted at 14 and 42 DAT on a 0 to 100 scale, where 0 = no injury and 100 = plant death, as compared to the non-treated control plots. Phytotoxicity ratings consisted of stunting and chlorosis ratings. Rice grain was harvested from each plot with a small-plot combine with a swath width of 2.3 m . Rice grain yield for both years was adjusted to 14% moisture.

Furthermore, the presence of these siRNA was correlated with cytosine methylation of the viral genome . This suggested that the Ty-1 gene is involved in transcriptional gene silencing . So far, little is known about the functional properties of the Ty-1 protein, and the nature of the signal transduction pathway involved in the defense response. Here, we generated cDNA libraries from samples of inoculated stems and newly emerged leaves of the near isogenic lines LA3473-R and LA3474-S, respectively. We used an RNASeq approach to identify differentially expressed genes during the resistant and susceptible responses to TYLCV infection. Finally, we cloned and sequenced the Ty-1 gene and determine some properties of the Ty-1 protein to provided further insight into how some of the newly identified DEGs participate in the TYLCV-mediated defense response. These results will be discussed in terms of the mechanism of resistance and associated signal transduction pathways.NILs of tomato with the Ty-1 gene or ty-1 gene were used for these experiments . Seeds of these NILs were obtained from the Tomato Genetics Resource Center, UC Davis. Tomato plants of both lines were grown in a greenhouse, allowed to be self-pollinated and fruits were harvested. Seeds were extracted and treated with 2.7% sodium hypochlorite for 30 min and rinsed with MilliQ water. Treated seeds were planted into sunshine mix 1 potting mix in a controlled environment chamber .To confirm the resistant and susceptible phenotypes of plants produced from increased seeds, NILs LA3473-R and LA3474-S, respectively, seedlings at the three- to five-leaf-stage were agroinoculated with cell suspensions of a strain of Agrobacterium tumefaciens containing a binary plasmid with the multimeric infectious clone of TYLCV from California by needle puncture inoculation of the stem just beneath the shoot apex .

The positive control in these experiments were seedlings of the susceptible tomato plants cv. Glamour agroinoculated with TYLCV, whereas the negative control was seedlings agroinoculated with the empty vector . Inoculated plants were maintained in a controlled environment chamber, and symptom development was assessed visually and recorded at 7, 14 and 21 d post infection based on the severity scores described in Lapidot et al. . Absolute viral DNA accumulation was quantified at 7, 14 and 21 dpi by quantitative polymerase chain reaction tests according to the protocol described by Mason et al. . Total genomic DNA was extracted from newly emerged leaves according to the method of Dellaporta et al. . A virus-specific primer pair for qPCR detection was designed to direct the amplification of an ~150 base pair fragment from the capsid protein gene of TYLCV . The specificity of this primer pair was predicted based on BLAST search , and confirmed experimentally by conventional PCR with DNA extracts of tomato plants agroinoculated with TYLCV and non-inoculated plants. The PCR-amplified TYLCV fragment was cloned into pCR-Blunt II-TOPO to generate a standard for qPCR assays. Recombinant plasmids containing the cloned PCR-amplified TYLCV fragment were quantified with a NanoDrop1000 spectrophotometer , and plasmid copy number was adjusted to 107 copies/µl with the Avogadro’s constant . Standard curves for qPCR were prepared with tenfold serial dilutions ranging from 101 to 106 copies of plasmid DNA. These standard curves were used to estimate the viral Cn for each sample. The qPCR was conducted on a QuantStudio 6 Flex Real-Time PCR System with 100 ng of total genomic DNA in a 20-μl reaction mix with the SsoFast EvaGreen Supermix kit . To detect the presence of the Ty-1 or ty-1 genes in the NILs LA3473-R and LA3474-S, respectively, restriction fragment length polymorphism analyses of the amplified fragments with a marker to Ty-1/ty-1 alleles were performed.

Here, leaf samples were collected from non-inoculated leaves of LA3473-R and LA3474-S plants and total genomic DNA was extracted as previously described. PCR tests were performed with the C2_At5g61510- F/C2_At5g61510-R primer pair , which direct the amplification of an ~1.0 kb fragment. PCR-amplified fragments were purified with the QIAquick gel extraction kit and digested with the five-base-cutting enzyme HinfI and the reaction analyzed by agarose gel electrophoresis.For the RNA-sequencing experiments, a cell suspension of an A. tumefaciens strain containing the multimeric infectious clone of TYLCV-[US:CA:06] or the empty vector was used for agroinoculation of seedlings of the NILs LA3473-R and LA3474-S as previously described. A total of three plants per treatment were inoculated per experiment, and the experiment was repeated three times. Tissue samples of the resistant and susceptible lines were individually collected and pooled together in each treatment from inoculated stems and, from other inoculated plants, from newly emerged leaves for a total of eight-time points . Samples were frozen immediately in liquid nitrogen. High-throughput RNA-seq library preparation was performed according to the method described in Kumar et al. . Briefly, double-stranded complementary DNA was prepared with random hexamer priming, and the resulting cDNA was fragmented, end-repaired and A-tailed. DNA barcodes for multiplexing Illumina DNA-Seq libraries were added to the cDNA fragments during adapter ligation, and the adapter-ligated cDNA libraries were enriched with 13 cycles of PCR amplification followed by size selection of ~200-500 bp fragments. A total of 96 cDNA libraries we generated, which included the eight-time points each for the resistant and susceptible lines and for the three independent experiments. Finally, barcoded libraries for each independent experiment were pooled together and sequenced on two lanes on Illumina HiSeq 2000 platform at the UC Davis Genome Center.Raw sequence data were filtered/trimmed for low-quality reads and technical sequences with Trimmomatic . Trimmed RNA-Seq reads were aligned to the high quality, non-redundant database generated from the tomato genome by the International Tomato Annotation Group with Hisat2 . The latest ITAG database was obtained from Sol Genomics Network . Feature Count was used to count the number of reads mapped to each gene . DEGs were identified with Cuffdiff, a method that estimates the relative transcript abundance . Gene expression levels were normalized with fragments per kilobase of exon per million mapped reads values, and the false discovery rate was used to determine the differentially expressed p-value threshold. In addition, an independent DEGs analysis was performed with DEseq and EdgeR methods , commercial indoor growing systems and data were visualized with Galaxy . In the present study, genes were considered to be differentially expressed only when their absolute value of log2 fold change was >1.5 and p-value was <0.05. To identify the potential function of DEGs involved in the Ty-1 resistance response to TYLCV infection, the functional classes of DEGs were identified with gene ontology enrichment analyses with PANTHER within the Gene Ontology project .

In order to investigate the transcriptional changes in tomato stems and leaves during TYLCV infection, we performed RNA-Seq experiments with inoculated stems and systemically infected leaves in the NILs LA3473-R and LA3474-S. Overall, ~1140 million read pairs were obtained for 96 libraries, with an average of ~12 million read pairs per library . The reads from these libraries were trimmed and then aligned to the tomato genome in the ITAG database. Time course comparisons of DEGs in the NILs revealed that the largest transcriptional changes in LA3473-R occurred at early stages of infection in inoculated stem tissues. A total of 797 and 660 genes were differentially expressed at 12 and 24 hpi, respectively, and dropped to 42 DEGs at 48 hpi . In the systemically infected leaves, there were substantially fewer DEGs, with 0, 44 and 10 genes differentially expresses at 7, 10 and 14 dpi, respectively . Most of the transcriptional changes observed in the LA3474-S plants occurred from 12 to 48 hpi in inoculated stem tissues and at 7 dpi systemically infected leaves. A total of 264 , 540 and 355 genes were differentially expressed at 12, 24 and 48 hpi, respectively . In systemic infected leaves, 356 genes were differentially expressed at 7 dpi, whereas 99 and 2 genes were differentially expressed at 10 and 14 dpi, respectively . Interestingly, a similar number of DEGs were induced in both resistant and susceptible responses, with 1553 and 1616 DEG in the resistant and susceptible lines, respectively. However, the percentage of upregulated genes in the susceptible LA3474-S line was higher, whereas more genes were downregulated in the resistant LA3473-R line . In order to gain insight into the mechanism or signal transduction pathway involved in resistance to TYLCV infection, we analyzed the transcriptome of resistant vs susceptible tomato plants at the eight time points during the TYLCV infection response following agroinoculation. DEGs in the resistant vs susceptible response to TYLCV infection were identified with three different statistical algorithms, and the analyses revealed 10751 genes differentially expressed by Cuffdiff, 5051 by Deseq, and 1462 by EdgeR, respectively . Moreover, a total of 679 genes and 58 lncRNAs were identified as differentially expressed in LA3473-R during TYLCV infection by all three methods . A large number of genes were differentially expressed at 24 hpi , but the largest transcriptional changes occurred at 7 dpi in systemically infected leaves, a time when TYLCV is accumulating in emerging leaves . In contrast, a total of 50 and 17 genes were differentially expressed at 10 and 14 dpi, respectively . To further study the TYLCV-mediated defense and susceptible responses in tomato during early and late infections, DEGs in protein families involved in stress responses in plants were selected for further analyses . Of the DEG identified by all three methods, 12 genes were associated with protein families involved in tolerance to abiotic stress response and plant-pathogen interactions, such as WRKY transcription factors, nucleotide binding site-leucine rich repeats proteins, receptor-like protein kinases , leucine-rich repeat receptor kinases and chloroplast proteins. In comparisons between resistant and susceptible responses to TYLCV infection, the mannose-1- phosphate guanyltransferase was upregulated 3.1-fold at 48 hpi, the heavy metal transport/detoxification protein upregulated 5.4-fold at 10 dpi and the WRKY transcription 46 upregulated 5.8-fold at 14 dpi . Comparisons between susceptible and the control revealed that Ycf68 chromosomal protein was upregulated 4.1-fold at 14 dpi; whereas the WRKY transcription factors 45 , 46 and 55 , two NBS-LRR genes , two LRR-RKs genes and one RLK gene were downregulated 1.6 to 6.7-foldat 14 dpi . Additionally, two lncRNAs were downregulated 2.5 to 4.0- folds at 14 dpi in the susceptible response to TYLCV infection . For a better understanding of the transcriptional responses to TYLCV infection in LA3473- R plants and to reveal putative functions of DEGs, GO enrichment analyses were performed with PANTHER and the tomato reference genome sequence. In these analyses, >80% of the DEGs, respectively, were annotated. Within the biological process class, the majority of DEGs belong to the category of cellular processes, metabolic processes and biological regulation .

As barb goatgrass and medusahead develop and change visually, other changes are less apparent, though important to consider, related to the nutritional quality for livestock grazing, ability of the individual plant to recover from defoliation , and the ability of the seed to continue to develop and later germinate after it is detached from the plant. While these changes are roughly predictable, variation from year to year, across regions, and even within pastures occurs due tovariation in weather, climate, landscape, presence of grazing, soil differences, and genetics. This means that predicting the timing for control can be somewhat imprecise, making the use of phenology observations imperative to optimize control treatments. University of California research conducted over multiple years describes how observations of plant growth stage can help to optimally time grazing and mowing treatments.The stages in table 1 provide a framework to describe how both of these species progress and change in their physical characteristics over the course of the growing season. The 12 stages are broken into vegetative stages V1 to V3, reproductive stages R4 to R9, a mature stage M10, a summer dry stage D11, and dead residual in the subsequent growing season at stage L12. Defining these stages helps to optimize the timing of grazing and mowing control treatments by defining the windows of susceptibility.During the first two vegetative stages the plants are very small and inconspicuous. They are often unnoticed when viewed on a landscape level and provide very little forage for grazing. When plants are grazed during these stages they will readily recover with new flowering stems; thus, little to no control is achieved. In order to impact plants heavily enough to prevent further reproductive stages from progressing, targeted grazing of the infested areas should begin during the late vegetative stage 3 or boot stage . Plants are affected by grazing from stage V3 until the reproductive stage 4 , when awns fully emerge, and neither grass species is palatable to grazing animals thereafter .

Crude protein of the vegetative grasses drops significantly from approximately 10 to 11 percent at the V3 stage to 7 to 8 percent at the R4 stage in the R8 stage , the seed is able to continue to develop and become viable if spikes detach from the plant. This can be visually approximated as the point that plant leaves and stem are turning brown, but the seeds and seed head are still green. The plant is fully mature once shades of red, brown, and green are apparent on the seed head . The window for treatment is much longer for mowing than grazing since palatability is not an issue.To better understand the timing of phenology of these two grasses in California, UC researchers measured the proportion of barb goatgrass and medusahead at various times through the growing season. Included were 18 locations in 11 counties from Shasta to Monterey at elevations from 80 to 990 feet above sea level during the growing season from 2006 to 2010. Whereas medusahead was present at all sites, barb goatgrass was present in samples taken from Tehama County to Yolo County. The limited range of sample locations for barb goatgrass reflected the more restricted range of this species compared with medusahead .Medusahead was sampled over a larger geographic range than barb goatgrass, and we therefore expected and observed more variability in the timing of phenology of medusahead relative to barb goatgrass. Medusahead became susceptible to grazing treatments from early or mid-April to early or mid-May, depending on the site and year. The transition from grazing susceptibility to only mowing susceptibility reliably occurred in early May and was usually complete in mid-May. Medusahead tends to enter the stage of maturity that is too late for effective mowing treatment between the last week of May and the first week of June. Some cooler locations in the Central Coastal valleys can be about a week later. In addition, there seem to be some locations with warmer winter temperatures and less moisture overall where this transition to maturity occurs much earlier, such as early May. Select sites in Glenn, San Joaquin, and Shasta Counties were consistently 2 to 4 weeks earlier than other sites. This may be due to a number of factors, including locally warmer spring temperatures. Barb goatgrass became susceptible to grazing treatments from mid-March to mid-April; however, grazing is not recommended at this time due to the existence of a dormant seed bank and less complete control compared with mowing, making this approach challenging. In 2007, barb goatgrass began developing notably later; 2007 was the only year when barb goatgrass collections made in late March and early April were not yet susceptible to grazing. During other years, the first collections made in early April were already susceptible to livestock grazing. The transition from susceptibility of grazing to only mowing reliably occurred in early May and was complete by mid-May. Generally, at all sites, barb goatgrass entered the stage of maturity that is too late for effective mowing treatment around June 1, with a variance of about 5 days. One year seemed to have more variability, with several sites maturing earlier and others sites later than other years. At the pasture scale, some individuals and patches of medusahead will mature more quickly than others due to variation in soils, slope, and aspect. In more-uniform pastures, most individual and patches of plants may be well synchronized, while in morevariable pastures there may be a greater range of stages at any given time in the spring. This can lead to patchy areas, with some grasses that are too early for treatment success and others that are too late for treatment success. Variable effects within pastures are amplified when they are not grazed. In these cases, managers will need to keep in mind that grazing should be considered a long-term approach that will not be fully successful every year .While the start of susceptibility varies substantially, commercial vertical hydroponic systems ranging from late March to early May, the duration of susceptibility for both barb goatgrass and medusahead tends to vary across its range and from year to year, but in somewhat predictable patterns.

The period of susceptibility of medusahead to targeted grazing is 2 to 3 weeks, while susceptibility to mowing of both species is about 5 weeks. The length of these periods varies by year, location, precipitation, and soils . Cooler spring seasons tend to lengthen the period of susceptibility relative to drier, warmer sites and years. Livestock stocked at moderate or light stocking rates will avoid medusahead and goatgrass particularly as plants transition fromV3 to R4. To overcome this aversion, heavy stocking rates that far exceed rates considered normal for annual rangelands are required to encourage enough consumption to impact seed production. For grazing to be successful, plants must be impacted enough to prevent the onset of seed set. This is possible because these two species tend to mature so late in the season that soil moisture is not present in adequate amounts for plant recovery , although this is not the case every year. The rate is determined by the forage biomass present, but it often exceeds 1 to 2 animal units per acre during the critical V3 and early R4 stages. This high rate is necessary because of the short window and amount of forage that needs to be removed. The objective is to consume forage biomass to, or even slightly below, 500 pounds per acre . This makes treatment site-specific within most ranches because of the difficulty of fencing, watering, and providing enough cattle to impact an area, as well as the increased management time. The short period of susceptibility for successfully implementing a grazing treatment can be overcome with mowing treatments. When implemented correctly, mowing is more likely to be a successful treatment than grazing because the timing will almost, but not always, prevent subsequent seed production. However, mowing faces other challenges, including the inability to cover steep terrain, rocks that damage the mower, and fire potential, which are very common scenarios on California rangelands. It is important to ensure that these treatments are applied as effectively as possible to get the most benefit out of them. By understanding the phenology of barb goatgrass and medusahead, these treatments can be better planned so that the timing and intensity of treatment corresponds to when they will most effectively reduce the abundance of these noxious annual grasses in the future.Grazing and mowing are two of many successfully tested weed control methods that can be used in combination with other methods for medusahead and barb goatgrass control. Using multiple methods is highly suggested for barb goatgrass areas. Ultimately, treatment decisions are site and management specific. Specifics on the effectiveness and implementation of the various other treatment options, such as burning and herbicide application, are available from sources such as Davy et al. 2008, DiTomaso and Kyser 2013, and Kyser et al. 2014. In addition, articles by Aigner and Woerly and James et al. have also assessed the effectiveness of different treatment tools on barb goatgrass and medusahead, respectively.Crops that grow vigorously can often outcompete weeds. Weeds grow best where competition is sparse; for instance, between rows or in gaps in a crop stand. Crops that are well adapted to their planted areas are often better competitors since they will tend to occupy a site rapidly. If you increase the density of the crop by decreasing the in-row spacing or by reducing the space between rows you will improve the crop’s competitiveness. A close-planted crop will close the canopy more rapidly, reducing the weeds’ ability to compete. Some crops compete effectively with weeds if given an early competitive advantage, while others never establish a competitive canopy. The use of transplants give the crop an advantage over the weeds because transplants enter the field larger and more developed that the weeds. With help from subsequent cultivation or hand weeding operations, a transplanted crop can develop a full canopy and crowd out weeds.Practices that reduce the production of weed seed also reduce weed pressure and can help keep weeding costs down over time. In an ideal situation, no weed would be allowed to go to seed. Any that do go to seed can aggravate weed problems for many years to come. As an example, common purslane seed has been shown to remain viable for over 20 years in the soil, and black mustard seed survives for over 40 years. The longevity of weed seed, together with the large numbers of seed produced by individual plants , can lead to the long-term build-up of enormous seed banks in the soil. If you make it a policy to remove weeds prior to seed production, you can reduce weed pressure in subsequent seasons.

A recently conducted needs assessment survey of 150 dairy producers in California demonstrated the importance of regionally targeted strategies, with the top 5 CE priority topics identified by respondents differing based on region . The northern San Joaquin Valley and greater Southern California regions were found to have greater similarities in priorities than the Northern California region, perhaps explained by differences in average herd size, type of production system, and climate . Because California agriculture is diverse and each cropping system will respond to change differently, adaptation research and effective stakeholder engagement should be regionally focused . In the rapidly changing context of California agriculture, identifying the relative importance of different topics is critical for prioritizing extension activities and making the best use of limited resources, while incorporating feedback from clientele will help to increase the effectiveness and impact of extension programs. Many forces beyond the farm level shape what is or is not possible on the farm, and there is a pressing need to understand how these forces intersect . New legislation, including the Sustainable Groundwater Management Act , which is the state’s first law regulating groundwater use in its history; new reporting requirements for the Irrigated Lands Regulatory Program; and new or impending agrochemical bans will shape the future of farming in California. Currently, it is unclear which issues are most pressing regarding grower management decisions and information needs. Equally important, the level of satisfaction with current extension activities is not well understood. Therefore, documenting the concerns and needs of growers, consultants, and allied industry will highlight the most important topics for research and extension to focus on, and guide policymakers and administrators on where resources and funding should be allocated.

Increases in California’s agricultural productivity have long been sustained by expanding water supplies, increasing use of fossil fuel energy, and new technology – all of which are now under pressure because of scarcity, cost, and public opposition . Now, more than ever, UCCE would benefit from a statewide understanding of common goals, challenges, and preferences for research and extension across different regions and crops to determine how innovative collaborations and partnerships might be established to meet clientele needs. While individual CE Advisors have conducted needs assessments for their clientele, to our knowledge there have been no prior efforts to comprehensively gather statewide information. Therefore, the primary objective of this study was to set research and extension priorities for agronomic crop production in California based on feedback and input from growers, their consultants, and allied industry professionals. The specific objective was to conduct a survey to i) identify top concerns and management challenges, ii) understand the motivations for growing agronomic crops and priorities considered in management decisions, and iii) prioritize information needs that can be addressed through research and extension efforts in the future.The needs assessment designed for this project was an online survey developed by members of the UCCE Agronomy Program Team and administered using Qualtrics survey software . The first step in developing questions was to collect and summarize previous needs assessments shared by individual members of the Agronomy Program Team for their specific crop or region. Based on overarching themes from past needs assessments and bearing in mind the objectives of this collaborative effort, questions were drafted and reviewed by a team of CE advisors and UC Davis faculty working in agronomic crop production.

Prior to launching the survey, it was piloted by 10 growers and other industry professionals. In depth phone conversations with pilot participants allowed for robust feedback that was incorporated into a final version of the survey. The final survey included a total of 21 questions, covering the areas of management challenges, concerns for the agronomic crop industry, motivation, importance of extension topics and level of satisfaction with UCCE. We also asked respondents who they communicate with about crop production practices and how they prefer to receive information. The survey was reviewed by the Institutional Review Board and approved as “exempt”. The needs assessment survey was a cross-sectional census survey attempting to collect as many responses as possible from anyone currently involved in agronomic crop production in California. We tried to ensure that we were getting accurate representation of California agronomic crops clientele by including a screening question. The survey link took respondents to a page asking if they grow, consult on, or work in allied industry of agronomic crops in California. If they responded yes, they were taken to the survey, and if they responded no, they were not able to continue. The first question on the survey following the screening question asked respondents to identify their primary vocation between “grower”, “consultant”, “allied industry”, or “other”. Depending on their response, we were able to direct management related questions specifically to growers, while still gaining insight from consultants and allied industry on broader topics. To identify concerns and challenges faced by those working in agronomic crop production, respondents were asked to rank their level of concern from a list of 15 topics that influence crop production in California. Next, respondents who identified as growers or consultants were asked to select their highest priority management challenges from a list of 8 common management challenges identified by our internal team of CE Advisors and CE Specialists. To understand the motivations for growing agronomic crops and priorities considered in management decisions, vertical farming equipment we asked respondents who identified as growers to rank how often certain factors affect their management decisions for field crop production . We also asked growers to select their primary reasons for growing field crops from a list of 9 commonly cited reasons, as determined by our internal team. To prioritize information needs that can be addressed through research and extension, we used Importance-Performance Analysis . This method is a quantitative approach for measuring how people feel about certain issues . The analysis generates a picture of how important specific topics are to clientele in comparison with how satisfying they are – or in this case, how satisfied clientele are with UCCE’s delivery of information on these topics . Typically, the visual output of this method is an IPA matrix created by plotting importance and satisfaction on a two-dimensional graph having four quadrants . The boundaries of the quadrants are based on the means of the two measures and each quadrant is interpreted as having implications for prioritization of information. The idea is that focus should be placed on topics found in the “high priority” quadrant, while resources can be allocated away from the “lower priority” quadrants . Focus should remain on topics that fall into the high importance and high satisfaction quadrant; however clientele is seemingly satisfied with UCCE’s work in disseminating information on these topics. Importance and satisfaction were each measured through a Likert-type scale, where participants were given a list of 19 topics commonly addressed by CE and asked to select if these topics were of “high priority”, “medium priority”, “low priority” to them. They also had the option to select “no opinion”, which received a score of zero. With the same list of topics, respondents were asked to select “high satisfaction”, “medium satisfaction”, “low satisfaction”, or “no opinion” based on how satisfied they were with UCCE’s delivery of information on these topics. High priority and satisfaction were given a score of 3, medium priority and satisfaction were given a score of 2, and low priority and satisfaction were given a score of 1. Scores for priority and satisfaction were averaged and plotted to create an IPA matrix. 2.2 Survey dissemination. The target audience of our online survey was all California agronomic crop growers, their consultants, and allied industry. Because no comprehensive list of such individuals exists, contact lists from individual agronomic program team members were compiled and duplicates were removed. In July 2020, stakeholders were sent an email invitation to take the online survey. The survey was open from July 23, 2020 until September 1, 2020 with three reminders sent to those on the centralized contact list, as suggested by the Dillman method to maximize response rate . The first 100 participants to complete the survey were also offered an incentive of a $10 gift certificate. As stated on the survey, all information was kept anonymous, and respondents were informed that the survey would be used to better guide UCCE research and extension efforts by highlighting the most important issues facing agronomic crop production in California and helping set priorities for future programming. While the centralized contact list contained statewide representation, the team decided that an aim of this needs assessment was also to reach people who UCCE might not already be serving. Therefore, to avoid excluding any potential respondents, the team developed a list of influential groups or organizations external to UCCE that could distribute the survey. This list included commodity boards, crop associations, Farm Bureaus, County Agricultural Commissioners, Water Quality Coalitions, and input distributors. These partner stakeholders were contacted and asked if they would be willing to share the survey with their clientele. If they agreed to share the survey, an anonymous link to the survey was sent to them for dissemination. The survey software was able to track which responses came from the original centralized contact list and which responses came from the anonymous link. However, with the anonymous link, the response rate could not be measured. Since our goal was to gather responses from a wide range of participants, we accepted this limitation in our methodology.Concerns varied by crop and region . For instance, the top categories for anyone identifying as a rice grower and rice consultant were “very concerned” about included regulations on chemical use , input costs , and regulations on water quality . The top categories that those growing or consulting on alfalfa were “very concerned” about included regulations on water use , water costs , and water quality . Respondents growing or consulting on wheat were “very concerned” about the commodity price of their crop , consumer demand , and availability of quality labor . Finally, corn growers and consultants were “very concerned” about regulations on water quality , availability of quality labor , and regulations on chemical use . All regions ranked “regulations on water use ” and “water costs” as the top concerns relative to other concerns. Based on mean responses, the greatest concern for regulations on water use was seen in the Southern San Joaquin Valley , the Intermountain region , and the Northern San Joaquin Valley , while greatest concern for water cost was observed in the same three regions: SSJV , Intermountain , and NSJV .

This is an area of on-going research in California and builds on programs developed in other regions. In processing tomato in Israel, for example, herbicides have been used to effectively and economically manage broomrapes in highly infested fields where eradication is no longer feasible . Growers found that pre-plant herbicide applications followed by complimentary post-transplant applications of acetolactate synthaseinhibiting herbicides such as sulfosulfuron provided control of Egyptian broomrape at both preand post-attached stages in tomato . The use of rimsulfuron as a pre-plant incorporated herbicide with a complimentary post-emergence application also provided good suppression of broomrape without causing significant damage to tomato plants . Some herbicide application protocols are based on the level of severity of broomrape infestation in tomato. For example, researchers in Israel have developed a thermal time-based decision support system named PICKIT that takes into account infestation levels and growing degree days since planting to guide the timing and rate of multiple herbicide applications for control of Egyptian broomrape; the system has been applied on a broad commercial scale . For severe infestations , growers apply sulfosulfuron three times post-planting at 200, 400 and 600 GDD, followed by overhead irrigation complemented by two foliar-applied doses of imazapic at a later growth stage. The DSS suggests that a medium level of broomrape infestation requires a single pre-plant incorporation of sulfosulfuron before planting tomato, followed by drip chemigation of imazapic at 400, 500, 600, 700 and 800 GDD, with two additional foliar imazapic applications at a later growth stage.

A similar DSS system is being tested on branched broomrape infestations in processing tomatoes in Chile and California with promising initial results .In California, only the rimsulfuron component of the PICKIT system is currently registered for use in processing tomato. Crop safety and registration support research is ongoing in California in an effort to register additional herbicides and application techniques in the event that branched and/or Egyptian broomrape problems expand in scale . A preliminary result from this research suggests that no visual injury and yield loss are associated with the use of the PICKIT system in local tomato fields .Cultural practice, such as rotating tomato plants with false hosts or non-host crops, could help with seedbank depletion, provided branched broomrape seed is not re-introduced to the field from outside. A trap crop is a species with root exudates that induce broomrape seed germination but the crop does not allow attachment or support broomrape seedling growth and survival. Potential trap crops for branched broomrape that can be used in a rotation are alfalfa , cowpea , green pea and flax . Tomato and other host crops should be excluded from the rotation for several years to encourage further depletion of seedbank with no chance of seed production. Since broomrape seed is very sensitive to flooding, incorporation of flooded rice into the crop rotation may also accelerate the depletion of soil seedbank . Soil fertility management can contribute substantially to the management of branched broomrape. Direct contact with fertilizer, such as urea and ammonium, may be toxic to broomrape, inhibiting seed germination and seedling growth . The negative effect of ammonium on broomrape is due to the plant’s limited ability to detoxify the ammonium compound using glutamine synthetase . Application of adequate fertilizer will not only ensure unhindered growth of the tomato plant; it will also minimize the release of the plant’s strigolactone, a root exudate that stimulates broomrape germination .

For example, it has been demonstrated that phosphate fertilization negatively impacts branched broomrape seed germination in tomato fields because of reductions in strigolactone exudation . Soil solarization has been shown to be an effective alternative to fumigation in reducing broomrape seed viability in areas with sufficiently hot climate. Solarization can significantly increase top soil temperatures up to 6 inches [15 cm] in depth when moist soil is covered with transparent polyethylene sheets for a period of one to two months. Dahlquist et al. reported 100% seed mortality of several weed species with solarization that raised soil temperature above 45°C for at least 96 cumulative hours. Mauro et al. found that soil solarization for two consecutive summers provided 99% mortality of viable seeds of branched broomrape in the seedbank without any negative impact on tomato yield. A recent field study conducted at UC Davis confirmed that soil solarization plus organic amends of either tomato pomace or plowed-down tomato plants can be used to substantially reduce the weed seedbank in general in tomato fields , although broomrape was not present at this site. One challenge in using this approach is the need to take tomato fields out of production for several months during the summer growing season in California. Additionally, it is not currently known if the elevated temperatures from solarization would penetrate deeply enough into the soil to provide adequate control of broomrape seed throughout the tomato root zone in an open-field production system. Other thermal methods of soil disinfestation, such as soil steaming, are another alternative to chemical fumigation. Soil steaming has been shown to be effective in controlling seeds of several weeds and other soil pest in California strawberry production . High soil temperatures of 158°F for 30 minutes can be regularly achieved in the field to a depth of 0 to 10 inches . This treatment seems to be sufficient to kill seeds of many weeds . Although the effect of this technique on broomrape seed mortality has not been studied, the small seed size of broomrape plants and their lack of protective tissues suggest that broomrape could be vulnerable to steam heating. However, like solarization, it is not known whether the depth of control from soil steaming would be sufficient as part of an eradication strategy for a quarantine pest like branched broomrape.Physical weed removal, such as hand weeding, particularly for a small infestation, can be part of an integrated approach to broomrape control. California is a state where hand removal of broomrape may be an option given the limited infestation level and widespread use of farm labor. The efficacy of hand weeding is highly dependent on thorough scouting and detection, drying rack for cannabis which can be very difficult given the plant’s small stature and the short period between its emergence and seed set . Deep inversion plowing would bury broomrape seeds to a depth below the soil layer where attachment to tomato root can occur . However, the dormancy and durability of broomrape seed in the soil seedbank would increase the risk of later broomrape re-occurrences. Physical removal and deep burial could be part of a management strategy if broomrape became too widespread for quarantine and eradication efforts to be feasible; however, because broomrape is an A-listed pest , physical removal and deep burial are not likely to provide a sufficient level of control alone.Biological control involves the use of biological agents or processes to damage seed, kill weedy plant or interfere with parasite-host relationships.

An insect herbivore, Phytomyza orobanchia, is known to be specific for broomrapes and feeds on broomrape ovules and seeds, thereby reducing broomrape seed production . Pathogens such as Fusarium sp. can be incorporated into the soil to control broomrape through an induced cytoplasm metabolism and endosperm cell wall degradation that breaks seed dormancy, thereby depleting the broomrape seedbank . Pathogen-based herbicides have been reportedly used to control young seedlings of parasitic weeds , and these bioherbicides can provide complete control of all emerged broomrapes if formulated with multiple pathogens . However, to date, no research on the applicability of these approaches in California cropping systems and broomrape infestation levels has been conducted, and they are not currently available for use. Cultivation of resistant tomato varieties would also be an effective approach to prevent parasitic effects of broomrape. Resistance to branched broomrape might be achieved by incorporating traits that prevent haustorium attachment and penetration, or tubercle formation; this approach has been demonstrated in broomrape-resistant sunflower . A group of scientists at UC Davis are currently screening a wide range of tomato varieties to determine their resistance to branched broomrape; results from this study could help to determine if enough genetic variability exists in tomato to use conventional breeding approaches to breed for broomrape resistance. Although screening is effective in small plots and is promising in the longer term, at present there are no effective commercial biological measures for broomrape control in tomato.The re-emergence and spread of branched broomrape are of great concern in tomato and other susceptible crop production systems in California. At this point in time, the problem is still relatively small. Current efforts are focused on quarantine and eradication using a regulatory approach and soil fumigation. These approaches depend on the reporting of new infestations and generally result in total crop loss to the grower and extremely high treatment costs. Therefore, success will depend on significant funding from state or industry sources to offset grower costs in order to ensure grower participation and reporting. In the event that broomrape problems in California expand beyond what can realistically be managed using quarantine approaches, management and mitigation approaches will be needed just like with other widespread weeds. Other countries have successfully demonstrated that an integrated approach on a long-term basis, involving outreach to growers, field scouting and detection of new infestations, mapping of contaminated areas and fields, equipment sanitation, manipulation of cultural practices and carefully timed herbicide treatments, among other treatments, can effectively reduce yield losses caused by branched broomrape. Significant research efforts are being made by a group of university, industry and regulatory scientists to develop detection and management approaches for branched broomrape and to modify existing approaches from other regions for adaptation in California.Across California, annual rangelands cover approximately 16 million acres and are among the most species-rich ecosystems in the state, supporting thousands of plant and animal species . California’s modern-day rangelands are largely dominated by nonnative annuals, which some believe replaced previously diverse native forb and grass communities . These naturalized annuals now provide a majority of the state’s livestock forage base. Currently, several noxious weed species are driving another transformation of California’s rangelands and pose a continued and growing threat to rangeland ecosystem functions and services . The spread of invasive weeds changes plant community composition and can lead to shifts in soil moisture and nutrient availability as well as the suppression of both native plants and other desirable and more palatable nonnatives, thereby reducing herbaceous diversity, wildlife habitat, forage quality and agricultural productivity . Across California’s annual rangelands, noxious weeds have been estimated to reduce livestock carrying capacity by as much as 50% to 80% .Two of the most prominent invasive species of concern are medusahead and yellow starthistle .

The studies need to analyze how actual tobacco industry practices contradict corporate schemes and their messages. Research is also needed to understand farmer and consumer perceptions of “ethically produced” cigarettes and how tobacco companies through these cigarettes undermine health policy, pass on misinformation, and build public faith in tobacco. Research is needed on how health policymakers and advocates view and participate in tobacco industry responsibility schemes. Research is needed on the direct links between tobacco industry practices and child labor, deforestation, and other realities of tobacco farming that clash with farmer welfare. Do tobacco companies knowingly purchase tobacco produced with child labor? What evidence is needed to verify that tobacco companies knowingly purchase tobacco produced with child labor? To what extent do companies’ policies and practices allow them to buy leaf produced with child labor? Policymakers and advocates need to examine opportunities for excluding imports of tobacco produced with child labor.Health policymakers and tobacco control researchers need to find a balance between building corporate accountability and recognizing tobacco companies’ efforts to cultivate tobacco and sell cigarettes. How should public health and tobacco control policymakers attempt to make tobacco companies accountable to child labor and other socially disruptive behavior without pressuring companies to move into more vulnerable societies where labor costs are lower and environmental standards are less restrictive or non-existent? What are experiences of tobacco farmers who contract directly with leaf companies and cigarette manufacturers? Is there transparency in contract agreements between farmers and tobacco companies? What remedies exist for tobacco farmers who have been entrapped through debts for marked up inputs from tobacco companies? What is the impact of contract farming on social development and environmental health in tobacco farming communities? Policymakers and researchers need to pressure tobacco companies to publicize details of tobacco farming contracts, average and enforced prices for inputs, and loans granted and collected to ensure fairness in contract arrangements. Cultural attitudes that support child labor need to be examined. What cultural attitudes, practices, and beliefs of tobacco farmers justify or sustain child labor? What cultural changes need to happen to mainstream, standardize, and normalize tobacco growing free from child labor and environmental destruction?

Research is needed on experiences of tobacco farmers and tobacco farm workers, recognizing that these economic groups have contradictory and overlapping interests. How many casual or day laborers work in the global tobacco growing sector? To what extent do farm workers use child labor and harm environments?How can public health policymakers and tobacco control advocates overcome ambivalence toward trade unions of tobacco farmers and farm workers that promote fair and decent work? Do health policymakers, advocates, and researchers develop partnerships focused on food security and sustainable agriculture with tobacco farm worker trade unions that lend support to tobacco industry social responsibility child labor projects? To what extent do health policymakers call upon trade unions that accept tobacco industry money and promote living wages to justify their policy of accepting tobacco money?The best practices for addressing tobacco-related child labor, deforestation and poverty involve equity and inclusivity. Equity in social protections such as quality education, health care, and housing and inclusivity of tobacco farmers in policy making processes and research activities in tobacco farming are major goals of best practices. The aims of best practices are to ensure prosperity and welfare of tobacco farmers, reduce the influence of tobacco companies on child labor and environmental projects, and in cases where tobacco companies financially support projects, obtain commitment from companies to support a program of outside, independent monitoring of compliance with global standards such as the International Labor Organization Convention No. 182 on the Worst Forms of Child Labor, 1999. Best practices to reduce tobacco-related child labor, deforestation and poverty are most effective when balanced with specific country experiences and policy priorities. Child labor in Malawi and child labor in India are different, requiring analyses of local contexts, stakeholder interests, and country needs. Deforestation in tobacco growing sectors in Tanzania and Brazil is not the same. The best practices below need to be examined in specific country contexts and implemented to ensure compatibility between best practices and policy environments.The International Labor Organization, International Program on the Elimination of Child Labor with projects in 88 countries, including many tobacco growing countries, is an example of best practices to address child labor in tobacco growing. The Dominican Republic provides a representative case of ILO-IPEC tobacco related research. In 2004, research was conducted to generate data on the extent and nature of youth and their families working in tobacco plantations in the Dominican Republic. One hundred children performing tobacco-related jobs were interviewed and fifty focus groups discussions were conducted on 35 farms. The main finding of the study is that child laborers perform poorly in school and have low attendance rates in schools because of their involvement in tobacco cultivation. The researchers recommended that non-tobacco agricultural development needs to be created and mechanisms to monitor and inspect child labor on tobacco plantations are required. The study provides a best practice approach to research that could provide basic information on the child labor problem in order to assess the extent and impact of child labor in tobacco growing countries. ILO-IPEC works in partnership with and receives financial support from global tobacco companies through the Elimination of Child Labor in Tobacco Growing Foundation , a tobacco industry funded group, raising the issue that tobacco control policymakers and researchers need to weigh the advantages and disadvantage of involvement with social, development, cannabis dry racks and environmental groups that collaborate with tobacco companies. Beginning in 2002, ECLT financially supported ILO-IPEC projects to reduce tobacco-related child labor in countries such as the Dominican Republic, Indonesia, and Tanzania. ILO-IPEC/ECLT studies appear to document child labor problems in a reasonable manner.

The major weakness of ILO-IPEC/ECLT studies is the absence of information and comment on tobacco companies’tobacco growing practices that harm farmers, children and environments, and companies’ strategies to use corporate social responsibility schemes to build faith in the tobacco and deflect criticism of tobacco companies’ practices. ECLT on its website states that the International Labor Organization plays an advisory role to ECLT. On ILO-IPEC website, ECLT is listed as a donor to ILO-IPEC in 2002-3 and 2006-7. ECLT through ILO involvement obtains legitimacy for ECLT and tobacco companies social responsibility schemes focused on child labor to sidestep labor exploitation in Malawi and other countries where ECLT operates child labor projects. The WHO is not a participant to ILO-IPEC. Industry funded child labor projects create a unique problem for health policymakers and tobacco control researchers that support WHO’s Framework Convention on Tobacco Control. Involvement of health policymakers and researchers in ILO-IPEC/ECLT projects could enhance legitimacy of tobacco industry efforts to promote goodwill and build public faith in tobacco through child labor projects. Refusal of health policymakers and researchers to participate in ILO-IPEC/ECLT child labor schemes creates a gap between the goals of policymakers and researchers to promote farmer prosperity and resources to reduce inequalities and improve living standards on tobacco farms.The hazard rating matrix developed to assess work performed by children in vegetable farming in the Philippines provides a simple tool tobacco control policymakers and researchers could use to assess work performed by children in tobacco cultivation . The hazard rating matrix is a specialized checklist and classification scheme comprised of work environment, materials and equipment used, and contact with social and water. The hazard rating matrix of the degree of safety of working conditions and the intensity of work could allow policymakers and researchers to identify hazardous work of children in tobacco growing that should be banned.78Promoting the creation and dissemination of documentary films about tobacco in Argentina as well as films about tobacco related child labor, deforestation, pesticide pollution and nicotine poisoning in Malawi, Tanzania, Mexico, Brazil, and Bangladesh. The Instituto de Ciencia y Tecnologia Regional in Jujuy, Argentina, coordinates projects to develop leadership among the youth regarding tobacco control through research, identify risk factors such as poverty that factor in the uptake of tobacco use in displaced aboriginal youth, and to raise community awareness and support for improved livelihoods of tobacco farmers in Argentina. In 2004, the Instituto de Ciencia y Tecnologia Regional produced the documentary film “Tabaco, Voces Desde El Surco” on tobacco farmers and workers in Jujuy to educate Argentineans and the international community about the social and environmental costs of tobacco farming. The video is available for viewing on the Internet, providing visual imagery of human experiences of tobacco farming to researchers, policymakers, and individuals with Internet access throughout the world. In the video, a tobacco farmer standing with a hoe in a tobacco field says, “One starts learning from very young when you are eight or nine years old and gets together with friends. We play to put the tobacco leaves on the cane [drying sticks], and in this way you are brought up doing this work. Then, when you are twelve you do the work of an adult.” The video imagery of farming, child labor, and environmental destruction from tobacco farming augments text-based reports and statistical analyses of tobacco work to more fully assess the extent and characteristics of tobacco-related child labor and biodiversity loss. In Malawi, the Guernsey Adolescent Smokefree Project established in 2006 the project “Ana a topa” to support children who work in the tobacco farming sector. Guernsey is a British Crown dependency in the English Channel near Normandy, France. “Ana a topa” involves a partnership between the Guernsey Adolescent Smokefree Project and the Tobacco Tenant and Allied Workers Union of Malawi, the main tobacco farm worker organization in the country. “Ana a topa” is in its beginning stages of a crop diversification scheme that directly supports children in Malawi and a research project with local advocates to assess the frequency of child labor abuses in Malawi.The project is a unique tobacco farmer union-public health group alliance to raise awareness of child labor, reduce the factors that force parents to send their children to tobacco fields instead of schools, and strengthen the tobacco farm worker union’s child labor committees in tobacco farms to confront the child labor problem. The project is cross-national and involves a media campaign in Guernsey to educate youth on the working practices imposed by the tobacco industry on Malawi and the demands placed on children to work in tobacco fields. In Uganda in 2004, the Environmental Action Network developed a project to create a database of information on deforestation and other issues affecting tobacco farmers. The project filled a local knowledge gap on environmental problems relating to tobacco by systematically collecting and organizing data specific to Uganda, allowing researchers and advocates to reduce dependency on data from other countries.

The recovery in water samples was on average 79%.A significant increase in sweet potato [Ipomoea batatas Lam.] production area in the southeastern United States has occurred in the past decade, increasing from 33,548 ha in 2007 to 51,800 ha in 2017 . Sweetpotato has proven to be a valuable crop with a national farm gate value of $705.7 million in 2016, up from $298.4 million in 2006 . North Carolina is the largest sweetpotato-producing state, accounting for 54% of U.S. production . North Carolina, California, Mississippi, and Louisiana account for 94% of sweetpotato production in the United States . Unfortunately, due to its prostrate growth habit and relatively slow growth, sweetpotato does not compete well with problematic weeds, resulting in reduced yields . Palmer amaranth and large crabgrass [Digitaria sanguinalis Scop.] are among the top five most common weeds in North Carolina sweetpotato, with A. palmeri being identified as the most troublesome weed . Amaranthus palmeri has been reported to be taller, to have a faster growth rate and greater leaf area, and to produce more overall biomass when compared with other Amaranthus species . Season-long A. palmeri interference is seen in vegetable crops, with reduced yield of 94% in bell pepper , 67% in tomato , 36% to 81% in sweetpotato , with the greater yield losses associated with higher A. palmeri densities. Limited herbicide options exist for use in sweetpotato . Growers rely on PRE herbicides, which do not always provide efficacious weed control and require rainfall for activation. POST herbicide options for A. palmeri control in sweetpotato are limited to between-row applications of carfentrazone or glyphosate . The lack of POST herbicides forces growers to use tillage for control of weeds until row closure, at which time growers have no additional control options for dicotyledonous weeds other than mowing weeds above the cropcanopy and hand weeding, which is a costly control measure . Digitaria sanguinalis is commonly found in fruit and vegetable crops but has not been highly ranked as a problematic weed due to efficacious POST herbicides such as clethodim, fluazifop, or sethoxydim . Although these graminicides can be effective, grasses escaping herbicide application or sprayed after substantial establishment may continue to compete with the crop and reduce yields.

Furthermore, herbicide resistance management for D. sanguinalis should be considered, as resistance to acetyl-CoA carboxylase herbicides, including those registered for use in sweetpotato has been reported . While its impact on sweetpotato has not been reported, season-long, D. sanguinalis reduced yield in bell pepper by 46% , snap bean by 47% to 50% , and watermelon [Citrullus lanatus Matsum. & Nakai] by 82% . A better understanding of the interactions of A. palmeri and D. sanguinalis with sweetpotato would allow for better decision making regarding their control. Thus, the objectives of this study were to determine the effect of five densities of A. palmeri and D. sanguinalis on sweetpotato biomass and storage root yield and quality, the intraspecific response of A. palmeri and D. sanguinalis across five densities with and without sweetpotato, and the effect of sweetpotato on growth of A. palmeri and D. sanguinalis.Field studies were conducted with ‘Covington’ sweetpotato at the Horticultural Crops Research Station near Clinton, NC on a Norfolk loamy sand with humic matter 0.31% and pH 5.9 in 2016 and an Orangeburg loamy sand with humic matter 0.47% and pH 5.9 in 2017. Nonrooted ‘Covington’ sweetpotato 20- to 30-cm-long cuttings were mechanically planted approximately 7.6-cm deep into ridged rows 1 m apart in the entire study at an in-row spacing of approximately 30 cm on June 9, 2016, and June 12, 2017. At 1 d after transplanting, sweetpotato plants were removed by hand in the no-sweetpotato treatments. On the same day, treatment rows assigned A. palmeri or D. sanguinalis were broadcast seeded on the soil surface and lightly raked to a depth of approximately 1.0 cm. After weed seeding, the entire study was irrigated with 1.3 cm of water using overhead irrigation to aid in weed seed establishment. No additional irrigation was applied, in either year, after the initial irrigation event. Treatments consisted of a single weed species at five weed densities grown with and without sweetpotato arranged in a randomized complete block design with three replications . Amaranthus palmeri and D. sanguinalis were hand thinned to treatment densities of 0 , 1, 2, 4, and 8 and 0 , 1, 2, 4, and 16 plants m−1 of row, respectively, when A. palmeri was approximately 8 cm tall, and D. sanguinalis had two expanded leaves. At the time of weed thinning, sweetpotato averaged one to two newly expanded leaves on each plant. Densities of A. palmeri and D. sanguinalis were based on those used in previous research . Plots consisted of two bedded rows, each 1-m wide by 5-m long, with the first row being a weed-free buffer row planted to sweetpotato and the second row a treatment row. Treatment rows were maintained at specific weed treatment densities, and border rows were maintained free of weeds season-long by weekly removal by hand. Season-long rainfall and growing degree day data are presented in Table 1. Two days before sweetpotato harvest, 5 sweetpotato plants and 5 plants of each weed species were randomly harvested at the soil level from each plot to determine aboveground biomass. Samples were placed in 2-ply paper yard waste bags measuring 40 by 30 by 89 cm and fresh biomass was recorded. Samples were then placed in a propane-heated, forced-air drier for 96 h at 80 C. Once dry, samples were removed and weighed immediately to determine dry biomass. To determine fresh and dry sweetpotato and weed biomass on a per plant basis, total sweetpotato or weed biomass within a treatment and replication was divided by the number of plants harvested. To determine dry biomass per meter of row, individual weed biomass was multiplied by sweetpotato plant and/or weed number in 1 m of row, respectively.

Sweetpotato storage roots were harvested at 113 d after transplanting in 2016 and at 107 DAT in 2017. In both years storage roots were harvested with a tractor-mounted two-row chain digger and hand sorted into jumbo , no. 1 , and canner grades and weighed. Total marketable yield was calculated as the sum of jumbo and no. 1 grades. Data for crop biomass, vertical growing weed individual weed biomass, weed biomass per meter of row, yield, and quality were subjected to ANOVA using PROC MIXED in SAS . Treatment, year, and treatment by year were considered fixed effects, while replication within year was treated as a random effect. Year was treated as a fixed effect to further evaluate components of the year by treatment interaction, such as year by weed density and year by crop presence or absence. If the treatment by year interaction was not significant, a contrast statement was used to test for a linear trend for dependent variables with increasing weed density, calculated separately for each weed species. All response variables, except canner yield, were square-root transformed to reduce both data skewness and variance heterogeneity before carrying out the mixed model ANOVA.Marketable yield decreased as the density of A. palmeri or D. sanguinalis increased. No treatment by year interaction for sweetpotato yield was observed ; therefore, data were combined over years. Marketable yield loss associated with A. palmeri density ranged from 50% with 1 A. palmeri plant m −1 of row to 79% with 8 plants m−1 of row, respectively, when compared with the weed-free check . Marketable yield reduction by D. sanguinalis was similar to marketable yield reduction caused by A. palmeri but at higher weed densities. Marketable yield was reduced by 35% and 76% with 1 and 16 D. sanguinalis plants m−1 of row, respectively . Loss of jumbo yield is a significant contributor to overall marketable yield loss at weed densities as low as 1 plant of either species m−1 . Jumbo grade had greater yield loss with 1 plant m−1 for A. palmeri and D. sanguinalis than the no. 1 gradefor both weed species at the same density . Results for estimated marketable yield loss per weed as weed density approaches zero for A. palmeri and D. sanguinalis were 119% and 61%, respectively. The higher estimated marketable yield loss as weed density approaches zero for A. palmeri relative to D. sanguinalis indicated higher competitive capacity of A. palmeri at low densities. These results for A. palmeri are consistent with another study in sweetpotato but higher than in soybean [Glycine max Merr.] , peanut , and corn . Estimated yield loss as weed density approaches zero in the present study indicates that A. palmeri and D. sanguinalis, even at low densities, can greatly reduce sweetpotato marketable yield. The initial yield loss as weed density approaches zero for D. sanguinalis was less than A. palmeri at lower densities. However, sweetpotato yield loss from interference byD. sanguinalis was higher than yield loss reported in snap bean . For parameter A, the asymptote of the regression model estimating the maximum yield loss due to weed density was 87% for A. palmeri and 83% for D. sanguinalis. Meyers et al. estimated a maximum marketable yield loss of 90% at A. palmeri densities of 6.5 plants m−1 of sweetpotato row. Findings from our study further support the findings of Meyers et al. , who also reported the highly competitive nature of A. palmeri with sweetpotato. To reduce interference of A. palmeri and D. sanguinalis, which are commonly reported in sweetpotato, growers should use a combination of efficacious PRE herbicides, as outlined by Meyers et al. , in combination with tillage, hand removal, and mowing . Although POST herbicides for A. palmeri are limited, POST herbicide options for selective grass control in sweetpotato are available and should be used when D. sanguinalis is less than 10 cm to minimize yield loss. If D. sanguinalis resistance is suspected, then alternative methods should be analyzed for control. Growers should not dismiss the impact of either weed, as a single A. palmeri or D. sanguinalis per meter of row reduced marketable yield by 50% and 35%, respectively . Reduction in marketable yield loss was due to a decrease in weight of no. 1 and jumbo sweetpotato grades.

Twenty seeds were sown in each smaller container by placing the seed on the soil surface in a shallow flood onto the soil surface. The larger containers were immediately filled with water up to 10-cm above the soil level and maintained at that level throughout the study. Starting after the day of seeding, each smaller container was treated as a plot and was set in a completely randomized placement and rerandomized every seven days. Copper sulfate crystals were applied by hand at 13 kg ha-1 three DAS for control of algae in each container for each run. The emerged rice seeds were counted before the pendimethalin applications and at 21 DAT to calculate the percent rice stand survival. At 20 DAT, plant height was measured from the soil surface to the far most extended leaf end in each plot. At 21 DAT, above ground biomass was harvested from each plot and dry biomass was recorded. The greenhouse was maintained at 33/25 ± 2C day/night temperature. A 16-hr photoperiod was provided and natural light was supplemented with metal halide lamps at 400 µ mol m-2 sec-1 photosynthetic photon flux. The CS formulation was applied using a track-sprayer at 187 L ha-1 with a single 8001EVS nozzle by placing container inside the spray chamber with a height of 43 cm from the surface of the floodwater to the spray nozzle. The GR formulation was spread by hand in each respective tub, calculated by the area of the larger plastic container.All statistical analysis was conducted on R with the use of the LMERTEST and EMMEANS packages . Data was subjected to linear mixed effects regression models and mean separation, when appropriate, with Tukey’s HSD at α=0.05. In the field study, the model consisted of the three formulations, three rates, three application timings as fixed factors, and assessment dates as repeated measure, while replications were set as random separately each year. In the greenhouse study, the model consisted of two formulations, two rates, two application timings, and five cultivars as fixed factors, while experimental runs were treated as random.

Normality of distribution were visually examined with quantile-quantile plots and linearity were visually examined by plotting residuals.There was interaction by year for Echinochloa spp. control . In 2020, 330 ± 8 Echinochloa spp. plants m-2 was observed in the non-treated, while in 2021, 180 ± 2 Echinochloa spp. plants m-2 was observed by 56 DAT . The field site previously recorded variations in weed species populations by year caused by differences in weather conditions and soil seedbank . The cyhalofop and propanil application influenced the grass control levels observed in 2020. Interaction effect across formulation with timing were observed for Echinochloa control both years . The interaction of formulations with timings in 2020 demonstrated a reduction in Echinochloa control as application timing was delayed from 5 to 15 DAS with theEC formulation; however, the differences were not observed after application of GR and CS formulations . In 2021, the interaction of formulations with timings demonstrated a decrease in Echinochloa control as application timing was delayed from 5 to 15 DAS with the EC and CS formulation, but again not with the GR formulation . Application rates impacted grass control across timings in 2020 and across formulation in 2021 Interaction of rate with timing in 2020 and rate with formulation in 2021 were observed . The Echinochloa control results are not consistent with Ahmed and Chauhan findings who repeatedly demonstrated an increase in grass control with an increase in pendimethalin rates in a dry-seeded rice system. In the water-seeded rice system, pendimethalin degradation will be increased compared to a dry-seeded system ; therefore, greater pendimethalin rates may be necessary to observe an effect. Transformations on the sprangletop control data did not help meet the assumptions of normality of distribution; therefore, the data is presented as if normality was met. Only pendimethalin timing and rate appeared to affect sprangletop control .

The bearded sprangletop population is minimal and previously observed by Brim-DeForest et al. . Therefore, the control results from pendimethalin may not be comparable to fields with greater sprangletop pressure and because of the population differences each year control levels are unclear. In this study, the flood was continuous and pendimethalin application was into the water. The flood may have also been a factor in suppression of sprangletop .There was treatment interaction by year for visual rice injury but not across assessment dates . Injury differed across formulation, rate and timing . Rice treated at the 15 DAS timing had the lowest injury levels, but differed across formulations . Theresults demonstrate that different formulations resulted in varying rice injury levels, which is similar to the results of Hatzinikolaou et al. who evaluated pendimethalin injury on various grass crop species. In 2020, tiller counts ranged from 30 to 200 tillers m-2 . In 2021, however, tiller counts were higher, ranging from 200 to 500 m-2 . After a GR and CS application, rice tillers were similar across timings; however, after EC application at 15 DAS tillers was higher. The rice treated at 15 DAS produced similar tiller numbers when treated at 10 DAS but not when treated at 5 DAS with pendimethalin applied at the 2.3 and 3.4 kg ha-1 from the EC formulations . Differences in formulations by application timings was evident and resulted in varying injury levels effected by the formulation. The greater weedy grass pressure in 2020 may have been a factor in the increase on visual rice injury and decrease in rice stands compared to 2021. Rice treated with pendimethalin showed increased injury with increasing rates when applied at the 5 and 10 DAS; however, at 15 DAS, injury was similar across rates, which suggests that after rice reaches the 3- to 4-leaf stage, rolling benches pendimethalin injury may not impact rice development. Absorption of pendimethalin can cause greater growth disturbance at earlier seedling stages when the grass seedling coleoptile is emerging at the surface of the soil and comes in contact with the herbicide as demonstrated by Knake and Wax with the grass weed, giant foxtail. Pendimethalin remains on the upper soil surface due to its physico-chemical properties ; therefore, once the seedling growing points are further above the soil surface there is a potential to overcome pendimethalin injury.An interaction in year was observed for grain yield. Interaction effect by formulation with timings were observed for grain yield . In both years, rice grain yield was similar across timings with the GR and CS formulations, but not with the EC formulation . Timing was most influential on grain yield with the EC. Overall, similar grain yield was achieved from rice treated with the GR across all rates and timings in 2020 and similarly in 2021 . The GR is formulated as a slow-release of the active ingredient which results in a reduction of crop injury . These characteristics of the GR may have allowed more rice seedlings to establish by not being exposed to high concentrated levels of the active ingredient at once. There was a rate by timing interaction for grain yield . Rice treated with 1.1 kg ha-1 at all timings produced similar grain yield in both years, which were similar to yield in plots when treated with 2.3 kg ha-1 at 10 and 15 DAS, and with 3.4 kg ha-1 at 15 DAS . Pendimethalin applied to rice at 3.4 kg ha-1 at 15 DAS timing had greater yield by 3,014 kg ha-1 of grain in both years when compared to the 5 and 10 DAS timings at 3.4 kg ha-1 .

The results demonstrate that formulation, rate and timing are important factors affecting grain yield in water-seeded rice with use of pendimethalin. An application of pendimethalin in dry-seeded rice in Bangladesh decreased grain yields by 44% to 50% when pendimethalin was applied 2 DAS compared to the weed-free check . Application timing or soil saturation timing is an important influence on rice injury after a pendimethalin application in dry-seeded systems . In the water-seeded system, application timing is the important factor. While not included in the analysis, the grain yields of the non-treated plots in 2020 were extremely weedy and attempts to harvest failed and yield was recorded as zero. In 2021, thenon-treated plots averaged yields of 2,450 ± 340 kg ha-1 . The yields recorded in this study after pendimethalin treatment were low compared to statewide average yields and potentially affected by the pendimethalin application.Stand reduction was influenced by cultivar, formulation, rate and timing . In general, rice treated at 5 DAS resulted up to 68% stand reduction across cultivars for both CS and GR formulations . At 5 DAS, stand was reduced after application of both formulations for ‘M-105’, ‘M-205’, ‘M-206’ and ‘M-209’ . Only ‘S-102’ at the 5 DAS timing resulted in less than 54% reduction . At 10 DAS, ‘S-102’ and ‘M-206’ did not show stand loss across rates, while ‘M-105’ resulted up to 21% decrease in stand after a 2.3 kg ha-1 application compared to a 1.1 kg ha-1 . However, stand reduction after 10 DAS applications were zero to 29% for all cultivars . Koger et al. observed differential cultivar response from pendimethalin applications on long grain rice in a dry-seeded system. Relative tolerance was attributed to mesocotyl length of seedling rice which may vary by cultivar; however, planting depth is also an important factor in dry-seeded rice for achieving pendimethalin tolerance . In water-seeded rice, a mesocotyl is very short on seedlings because the seeds are placed on the soil surface; however, differences in seedling vigor can be important for relative tolerance to pendimethalin. Ceseski and Al-Khatib observed ‘M-205’ and ‘M-209’ to have greater seedling vigor when compared to ‘M-105’ and ‘M-206’, when drill-seeded in a high clay soil. The cultivar vigor characteristic differences can help understand the observed relative tolerance to pendimethalin across cultivars in this Rice biomass was affected by pendimethalin rate and timing . The higher rate was an important factor in decreasing biomass for ‘S-102’ at the 5 DAS from CS and GR applications at 2.3 kg ha-1 . Dry biomass was reduced by 77% at 5 DAS compared to the 10 DAS timing averaged across formulations, rates, and cultivars. However, biomass reduction was minimal and not significant at 10 DAS, except for ‘M-205’ at 2.3 kg ha-1 GR formulation . Awan et al. observed a decrease in rice seedling biomass in dry-seeded rice when pendimethalin was applied at 2.0 kg ha-1 , but not at 1.0 kg ha-1 . Similarly, in this study biomass reduction was rate-dependent for ‘M-205’. Plant height was no different among treatments and were similar to the non-treated by time of biomass harvest .

A continued practice of cover cropping becomes an investment in building healthy soil over the long term, builds organic matter and by serving as food source to soil organisms , and increasing soil productivity . The initial year similarity in organic matter content levels of cover cropped and fallow plots is probably due to the fact that soil organic matter buildup takes place very slowly.Organic matter of a soil is important in improving soil structure, increase infiltration and cation exchange capacity and serves as efficient storage of nutrients . Upon its breakdown soil organic matter releases available nutrients to plants . However, soil contents of organic matter frequency and type of cultivation , cropping and residue management , or fertilizer N input may also affect soil nutrient status. The soil organic matter contents from cropping treatments were reflected in variation of some soil nutrient contents. As has been shown from soil nutrient analysis, nutrient enhancement from cover cropping was more visible following cover crop residue incorporation. Wagger and Creamer and Baldwin suggest that higher contents of soil nutrients were associated either manure applications or cover crop incorporations. While soil nutrient concentrations oscillated between sampling periods and years, Ca and Na concentrations and soil cation exchange capacities were higher for the cover crop treatments of the second year ABH sampling and at ACCP sampling in the third year. The higher soil nutrient concentration and CEC from the cover crop plots of the 2008 must have been from the accumulation from the previous year crop residue decomposition . However, most of the soil nutrient concentration right after cover crop incorporation of 2008 was not different among the cropping treatments, indicating the probability of nutrient immobilization following residue incorporations.

The latter increase in soil nutrition must have been from the mineralization process following cover crop residue decomposition. The trend suggests that it is possible to buildup up soil nutrient contents with the use of summer cover cropping and allow the subsequent vegetable crop to make use of accumulated soil nutrients. It also suggests that the process of cover cropping rotations must be continuous in order to achieve a continuous improvement in nutrient availability for the subsequent vegetable crop. Similarly, soil NO3 was consistently higher for the cover crop treatments relative to the summer fallow, but not until after cover crop incorporation of 2008. Soil NO3 level declined and was not different among the cropping treatments at ABH sampling of 2009. The decline in NO3 at broccoli harvest was probably depletion due to nitrogen uptake by broccoli. In relatively higher soil NO3 levels in 2009 than in 2008, suggests a nutrient build-up effect from repeated cover cropping and a higher N mineralization with increased years of residue accumulation. Soil SO4, and percent cation saturations were higher for the cover crop treatments, compared to the fallow, but not until 2009. Mn and B were higher in the fallow than in the cover cropped plots at harvest. My results demonstrated the importance of preceding cultivation of vegetable crops with summer cover cropping instead of leaving the land fallow. Following broccoli production after summer cover cropping benefitted the crop in enhancing and increasing soil nutrient availability, enhancing crop growth and marketable yield. The ultimate benefit of cover cropping may also come from pest suppression, enhancing beneficial organisms, increased biodiversity and other indirect benefits of cover cropping. Since soil nutrition is particularly critical for organic food production practices, the use of cover crops could help fulfill this need. I observed that not all soil nutrients are equally enhanced with the use of cover cropping. Besides, not all cover crops are equal contributors to added soil nutrition.

Increases in soil nutrient content, particularly soil NO3 was greater when the cover crop was cowpea than when it was a marigold, probably relating to the nitrogen fixing capability of cowpea. Leguminous cover crops with a biological nitrogen-fixing capability play a much more important role and may reduce dependence of the subsequent crop on synthetic nitrogen fertilizers . However, Franzluebbers et al. 1994; Fageria et al. 2005 all suggest that N supply from the decomposing residues must coincide with the subsequent crop N demand and proper management of residue in order to provide increased efficiency of cover crop use. The N supply from legumes could reduce N application rates below the recommended rate for subsequent vegetable crops . The contribution of N is the primary benefit of leguminous crops resulting in increased crop yields . Therefore, my findings of variable nutrient contribution from different cover crops suggest that the extent of soil nutrient build up is dependent on the type of the cover crops and that proper cover crop compatibility and selection be made based on the requirement of a farm and residue management practices. Although legumes could release fixed N to the soil, leguminous cover crop residues may also transport a large portion of their biomass nitrogen into the seeds if allowed to flower and mature, because the N-fixing symbiosis of the legume shuts down when the crop stops active growth. Therefore, a good management that benefits the subsequent vegetable crop is to kill the legume cover crops in the early- to mid-blossom stage and plant the following cash crop without delay, aside from any period for residue decomposition . Since soil nutrition is somewhat related to soil organic matter accumulations, such benefits must depend on a balanced interaction of organic matter, soil organisms that break down crop residues and nutrient cycling and selection of the cover crop and residue management practices . The increased microbial immobilization of soluble N may require modified fertility management practices that increases nutrient availability to coincide with plant demand . Immobilized nutrients may be subsequently available through mineralization after incorporation . On the other hand, the pattern and timing of mineralization of nutrients depends on the residue quality, soil type, temperature, soil moisture content and timing and method of incorporation . The higher soil Ca and Na under cover crop treatments may also be due to the fact that cover crops may help bring nutrients such as calcium and potassium back into the upper soil profile from deep soil layers and then release them back into the active organic matter when they die and decompose . As for the soil contents, higher N, Mg and Na were detected in the shoots of broccoli grown on the summer cowpea plots compared to the fallow treatments. However, vertical racks these nutrient increases were only in the 2009 crops, but not the 2008, indicating a need for repetitive and multiple-year cover cropping rotations to provide increased nutrient supply to the subsequent vegetable crop. In some cases, while some soil nutrients were higher for the cover crop treatments than in the bare soil, the subsequent crop does not seem to have made full benefit of the improved soil nutrition. My findings were consistent with Baggs et al. where no significant effect of cover cropping was observed on the N content or yield of the subsequent oats crop, regardless of the release of N from decomposing cover crop tissues.

These observations were attributed to non-limiting N in this soil for any benefits to become apparent immediately. It is also possible that mineralization of some nutrients from incorporated residues may be delayed , resulting in conflicting evidence over the ‗fertilizer value‘ of cover crops showed that recovery of N by the subsequent crop is typically less than 30–40%. Cover crops may also reduce available soil NO3 compared with the fallow treatment by 18–44% as a result of low mineralization rates.My observation of low nutrient content in shoots of crops and the many other previous findings suggest that crop nutrient contents do not necessarily match soil N contents. Baggs et al. showed that crop N alone is an adequate indicator of the quality of a cover crop. In some cases a higher N content in crops was observed following a bare ground treatment than the cover crops, suggesting that N was not available for crop uptake following cover crop incorporation and may be delayed until after complete mineralization . Nutrient immobilization from incorporation of residues is short-lived immobilization for soils with comparatively high C:N ratio . Cover crops can provide N to subsequent crops in two ways 1) non-legume cover crops recover and recycle residual fertilizer N, and 2) legume cover crops fix atmospheric N for the later crops . In general while cover crops have the potential to supply nutrients to the subsequent crops, synchronization of N supply from decomposing residues and crop nutrient demands must govern the timing of cover crop kill Creamer and Baldwin, 2000. If not properly managed cover crops create nutrient deficiency as a result of immobilization . This is probably the reason why Schroeder et al. rejected the use of cowpea crop residues as fertilizer N inputs for broccoli. Consistent with nutrient status, crop height growth was highest for those from cowpea, followed by marigold and least for crops grown on the summer fallow. The increase in height of broccoli grown on the cover crops is more prominent after the third week of sampling for all study years, but no height differences were observed between cropping treatments for the initial growth stages . This initial stage indifference in crop height could be due to a growth lag phase and that crops are not able to make immediate use of the added resources. Broccoli canopy spread was similar to the crop‘s height responses in that broccoli on the summer cover crop treatments for all years were relatively of broader canopy, but were most significant for the 2008 cropping year. Canopy growth differences between the study years may have been due to the variation in weather conditions of the different experimentation years. Mean leaf number production and variation between cropping treatments were clearly visible for the 2008 and 2009 cropping seasons than for the 2007 crops. These visible increases in number of broccoli leaves with increasing cover cropping rotations indicate the benefits of multiple cover cropping rations and their buildup effects with increasing use of the system. Regardless of some differences in various growth progressions of the vegetable crop, there were some similarities in their responses to the cropping system treatments. First, crop growth is most enhanced by preceding it with summer cowpea than marigold. Secondly, the taller and the greater the canopy spread of the crops are, the higher are the number of leaves per plant.

Three summer cropping treatments were employed: 1) French marigold , 2) cowpea , seeded at 56 kg/ha, and 3) a summer dry fallow as the untreated control. Cowpea was chosen because it is a drought hardy legume, weed drying rack resistant to weeds and enhances some beneficial organisms . Marigold was chosen because it is known to control nematodes . Each treatment plot was 12 m long x 10.7 m wide and laid out into 14 planting rows. The cover crops were direct-seeded in the last week of June in the center of the planting rows of each plot, watered through drip-tubing and grown for three months. The fallow control plots did not receive water during the summer. Each cover crop treatment plot was planted with the same cover crop in each of the three years of study. Plots were separated from each other with a 3 m wide buffer bare ground. The three treatments were replicated four times in a completely randomized design. At the end of the summer cropping period , the cover crops were mowed at the soil line, chopped, and the residues left on the ground. Concurrently, alternate rows of each of the cover crop treatments were incorporated into the soil at about 0.4 m intervals using a hand-pushed rotary tiller in preparation for broccoli transplanting. The fallow plots were not tilled. Plots for cover crop and broccoli planting are shown in Figure 1a. At the beginning of the subsequent cropping season , broccoli seedlings were transplanted in double rows into the tilled strips of the summer cover crop and fallow plots at an inter and intra-row spacing of 13 and 35 cm, respectively . Broccoli transplants were drip irrigated and fertilized with emulsified fish meal at 5 gallons/acre rate. Broccoli was chosen because it is a high-value vegetable crop that is sensitive to weeds, insect pests, nematodes , and requires high soil nutrients . All plot treatments were maintained in the same location for all three years of study in order to assess a cumulative effect of cover crops over time. During the third year of the trial I included testing nematode response with susceptible tomato plants. In three of the existing treatment replications, 5-6 tomato seedlings were inter planted into broccoli to observe if cropping treatment differences can be seen on tomato.

At broccoli harvest time , all tomato plants were uprooted and evaluated for tomato root nematode and assayed for gall index.Soil nematode population densities were determined by collecting 14 soil cores from 5-25 cm depth from each plot using a 2.5 cm-diameter Oakfield Model L and LS Tube-Type Soil Sampler. Soil samples were collected at cover crop planting , at cover crop incorporation and at broccoli harvest . In each of these years, the 14 soil cores were pooled for nematode analysis. Nematodes were extracted from a 100 gram sub-sample on modified Baermann funnels for 5 days and the number of nematodes was counted. Ten broccoli plants were removed at harvest from each treatment plot and rated for root-knot nematode galling on the 0 to 5 scale outlined by Taylor and Sasser . One hundred grams of broccoli roots were placed in a misting chamber for 5 days fornematode extraction and the number of second-stage root-knot nematode juveniles was counted. All data were analyzed using a one-way ANOVA analysis and means separated used the student T-test.Soil nematode population levels in the experimental field were generally low in all treatments during all years and all sampling periods. Observed plant parasitic nematodes were root-knot , cyst , and pin nematodes only. On any of these nematodes, there were no significant differences among cropping treatments at any sampling period or trial years . The huge variability of data among replications of each treatment and hence a high standard error made most of the differences statistically insignificant. However, there were some relative variations among the cropping treatments. The root-knot nematode population densities were relatively higher for the ACCI sampling of all years in the cowpea treatment compared to either marigold or the fallow treatment . The sugarbeet cyst nematodes were higher at the ABH sampling for the cowpea, relative to the other cropping treatments . When pooled for the three sampling periods, only RKNs were significantly greater in the cowpea plots for 2007 and 2009, but not 2008 . Neither the SCN nor the pin nematodes were significant for year or cropping treatments . If pooled for the cropping treatments , the RKN were denser for the cowpea treatment compared to marigold or fallow treatments .

The population density of RKN for the cowpea treatment was about 14 times higher than in the RKN population in the fallow treatment . The pooled mean population densities for the other nematode species were not significantly different among the cropping treatments . For the broccoli root analysis, neither of the broccoli nematodes nor the broccoli root gall index was significantly different among the cropping treatments or experimental years . Nematode root-gall formation on broccoli was generally very rare and only appeared during the first year and none during the subsequent vegetable growing years . When data were pooled for the sampling periods, and years, there were more RKN population levels on broccoli roots grown on the summer cowpea field than those grown on either marigold or fallow treatments .The last year trial using nematode-susceptible tomato plants inter-planted did not show any significant variation among the cropping treatments on the population density of any of the nematodes , although there were relatively more j2 RKN in the fallow plots than in either marigold or cowpea cover crop treatments. In general, rolling bench the results reveal that contrary to the hypothesis, the use of cowpea and marigold as an off-season cover cropping do not provide suppression to parasitic nematodes, at least to these observed within this experimental field. In most cases the cover cropping treatments had the same effect on parasitic nematode population densities as the fallow treatments. In rare cases, the cover crops enhanced the population densities of some parasitic nematodes compared to fallow treatment.While the effects of summer cover cropping treatments were not significant on the crop parasitic nematodes, they had significant effects in enhancing saprophytic nematode population densities . Enhancement of saprophytic nematodes started at the ABH sampling in the first year , with no significant differences among cropping treatments for the ACCI sampling. Data on saprophytes was not collected for the ACCP sampling in 2007. At the ABH sampling of 2007, saprophytes were about double on the cowpea treatment compared to the fallow , indicating the stronger enhancement of saprophytes with cowpea cover crop. Population densities of the saprophytes continued to increase in the second and third year compared to the 2007. Higher population were observed in both cover cropping treatments at the ACCP sampling of 2008 compared to the fallow , probably accounting for the previous year cover crop and broccoli crop residues. At this sampling period, saprophyte population were about 5 and 4 times higher in plots that had summer cowpea and marigold, respectively compared to the summer fallow . Regardless of the huge differences in saprophyte population densities among cropping treatments for the ACCI and ABH samplings of 2008, there were no significant differences among the treatments. Saprophyte population densities reached highest peaks following ACCI sampling in 2009 than any other sampling times of all years. At this sampling saprophyte populations were by far greater on the cowpea compared to either marigold or fallow treatments . However, there was a sharp decline in those nematodes for the ABH sampling of 2009 compared to the same time sampling in 2008 . When pooled for the three sampling periods , saprophytic nematode population levels were enhanced by both cover cropping treatments in 2008 and only by the cowpea cover crop in 2009 compared to the fallow system. Over all, cropping treatments had no significant effect in 2007 , indicating that the influence in cover crops on saprophytic population densities cannot be realized within one year of cover cropping rotations. If mean data are pooled just for the cropping treatments , both cowpea and marigold significantly enhanced saprophytes over the fallow treatment.Plant-parasitic nematode population densities in the experimental field were generally low during all years. There were only few species of plant parasitic nematodes, the root knot , cyst , and pin nematodes observed. The root knot and cyst nematodes are classified as the most dominant and economically damaging groups of plant parasitic nematodes . At all sampling times there was a huge variability in nematode population densities within the treatment replications, resulting in a large standard error and often leading to a non-significant effect in spite of large differences in mean values. Accordingly, the cropping treatments did not show significant differences on most nematode responses. Such problem may probably be minimized by using higher replication treatments . Furthermore, both cowpea and marigold cover crops are non-susceptible crops to nematodes and hence the reason for no significant differences among the cropping treatments. Broccoli crop is also a poor host to most nematodes and if planted late in the season when soil temperature is low, the nematode populations would also be low. Although a nematode susceptible crop was introduced by intercropping with broccoli at the third year, nematode population densities were still not variable among the cropping treatments. While cowpea and marigold cover crops are generally regarded as nematode resistant or suppressing plants, their use as off-season cover crop did not guarantee this value under this particular trial conditions. In some cases, RKN population densities were rather higher following cover crop incorporations, particularly cowpea, than under a fallow system. The relatively higher RKN following cowpea residue incorporations may indicate that cowpea still allows some level of nematode multiplication and thus is not resistant against RKN. It is also possible that the cover crops may have suppressed nematodes, but the initial low nematode population level in the field may have made it difficult to make a clear demarcation whether the cover crops suppressed nematode populations or not. Therefore, these responses basically contradict the previous findings that generally regarded cowpea and marigold as resistant and a potential means by which parasitic nematodes can be managed . Wand and McSorley observed that ‗Iron Clay‘ cowpea was susceptible to the same species of nematode it was once identified as suppressing. Chen et al. also showed that an increase in SCN population density in a former nematode suppressant perennial ryegrass treatment.