Progress 08/01/06 to 07/31/09
Outputs
OUTPUTS: In AR, a field experiment was conducted to determine the efficiency of Brassicaceae cover crops in converting glucosinolates to isothiocyanates (ITC), and their effect on weed suppression in plasiculture tomato and bell pepper. The major weed species were yellow nutsedge, Palmer amaranth, and large crabgrass. Eight different cover crops, Fumus FE75 and Fumus FL71 Indian mustard, Humus canola, Southern Giant brown mustard, Seventop turnip, herbcress, and Caliente (white and brown mustard blend) were drill seeded in spring. A second field experiment compared the economics of tomato production under cover crop-amended soil and standard MeBr fumigation using two different mulches. The test area contained yellow nutsedge, Palmer amaranth, johnsongrass, large crabgrass, and broadleaf signalgrass. Three different cover crops were drill seeded in mid-March. The plots were covered with LDPE or VIF mulch immediately after incorporation of cover crops. Fourteen 4-leaf stage tomato seedlings were transplanted one week after laying of plastic. One half of each plot was kept weed free by hand weeding while the other half was maintained as a weedy check. The time to weeding was recorded in the weed-free half of the plot, whereas the remaining portion of the plot was rated for crop injury and weed control every other week. Tomato fruit were harvested throughout the season and graded according to the USDA standards. The time of weeding and marketable fruit yield was recorded to compare the economics of weed suppression by the three cover crops relative to a standard methyl bromide treatment. Two additional field experiments were conducted to determine the optimum rate of allyl and phenyl ITC for weed suppression using standard LDPE versus VIF mulch. The major weed species in these experiments were yellow nutsedge, Palmer amaranth, and large crabgrass. Five rates of each ITC (0, 15, 75, 150, 750, and 1500 kg/ha) were evaluated along with MeBr plus chloropicrin at 390 kg/ha. Both ITCs were applied using a backpack sprayer and incorporated in the soil using a roto-tiller. Raised beds were prepared after ITC incorporation and covered with LDPE or VIF mulch. Seven tomato or 20 bell pepper were transplanted 3 weeks after laying the plastic mulch. Transplant holes were punched in the plastic 48 hr before transplanting to aerate the beds. Crop injury and weed control were visually rated. Tomato and bell pepper fruit were harvested and graded according to USDA standards. In NC, the research focused on phenyl and allyl ITC applied through drip irrigation under plasticulture. Both ITCs were evaluated at 0, 100, 500, 1000, 5000, 10000 n mol/g of soil. These treatments were evaluated with LDPE and VIF. The field had a natural population of purple and yellow nutsedge. The LDPE and VIF were laid over beds having one drip irrigation tape in the center of the bed. The drip tape was buried 1 inch deep. The fumigant was applied before nutsedge had pierced through the mulch. The fumigant was injected into the drip irrigation using fertilizer injector tanks. Amelia tomato and Heritage bell pepper were planted 3 weeks after application. PARTICIPANTS: Jason Norsworthy was the lead investigator and Sanjeev Bangarwa was the graduate assistant that completed much of the research in Arkansas. Integration of Brassicaceae cover crops or synthetic ITC with plastic mulches for weed control in plasticulture tomato and bell pepper were taught to students as part of the Vegetable Weed Control lecture in the Principles of Weed Control class at the University of Arkansas. In summer of 2009, findings were presented to attendees of a vegetable workshop in Fayetteville, AR. Additionally, the agronomic and weed management practices used in above experiments were demonstrated to the University of Arkansas Weed Team students to prepare them for the Southern Weed Contest from 2007 to 2009. Significant findings have been presented at various regional and national meetings from 2008 to 2009 (Please refer to publication section). In addition, results of synthetic ITCs were presented to attendees of the 2008 International Weed Science Congress. Research results have been shared with project collaborators in other states through the southern US. In North Carolina, David Monks and Katie Jennings oversaw the research. Findings from the research conducted on phenyl nd allyl ITC applied through drip irrigation were not promising, thus were not extended to growers. However, the information developed in the trials evaluating herbicides applied by drip irrigation has looked promising. Regional field days have occurred in 2008 and 2009 at Mills River, NC and we have presented this information to over 200 attendees (growers, faculty from other universities, industry personnel, etc). Attendees have been from around the S.E. U.S. This work will also be shared at various vegetable meetings in the upcoming year and will be shared through SEVEW. SEVEW is the Southeastern Vegetable Extension Workers and is made up of most vegetable specialists including pest management specialists in the Southeastern U.S. This work will also be written up for publication in a national journal so the results are available worldwide. TARGET AUDIENCES: Producers, county agents, university faculty and specialists, and industry personnel were the target audiences through field days and workshops. Additionally, students in weed science classes were educated about our findings. Furthermore, scientists around the world will have access to our findings through data that will be published in Weed Science, Weed Technology, and HortTechnology and through scientific presentations at regional, national, and international meetings (see publications). PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
In AR, no injury was observed from any of the cover crops, indicating that tomato and bell pepper are tolerant to ITC released by Brassicaceae cover crops. No difference was observed among cover crops in terms of yellow nutsedge shoots penetration through the plastic. Weed control from the cover crops was low, variable, and short lived. The most effective option for weed control was synthetic ITC. Phenyl ITC was more injurious to tomato and bell pepper, especially at higher rates. Injury can be minimized by aerating the planting beds by punching holes 48 hr before transplanting. Allyl ITC at 750 kg/ha provided excellent control of all weeds. Both ITCs at 750 kg/ha provided tomato and bell pepper fruit yield equal to MeBr. In NC, one complication was the ITC and water separated when put into the fertilizer injector tanks. Nonionic or COC was added to the tanks prior to pouring the ITC in the tank. These additives placed the ITC into solution temporarily. But injection of the chemical into the drip tape took 45 to 60 min so the ITC and water eventually separated. The tanks needed to be shaken continuously during the injection process. A second complication was the ITC melting the plastic injector lids that we used to inject the fumigant into the drip tape. This observation resulted in the 5000 and 10,000 n moles / g of soil treatments to be removed for the 2008 growing season. In 2007, we applied all 5 rates of allyl and phenyl ITCs. The 5000 and 10000 n mole treatments caused the plastic injector lids to melt. In 2008, the 5000 and 10000 n mole treatments were not applied. No tomato or pepper crop injury occurred either year. In 2007, allyl ITC at 5000 and 10,000 n moles / g of soil treatment applied under VIF had 25% nutsedge control. In both years, allyl ITC at 100, 500, and 1000 n moles / g of soil applied under both types of mulch did not control nutsedge. For both years, phenyl ITC did not control nutsedge at all rates under both types of mulch. The observations of lack of nutsedge control may have been due to the likely nonuniform distribution of ITC due to separation from water during injection. It does not appear that this method of application for these materials is a viable option for nutsedge control. These materials injected into a drip irrigation system are complicated to handle, and provide minimal nutsedge suppression or control when applied in this manner. At the same time that phenyl and allyl ITC applied through drip irrigation were being evaluated, the idea to evaluate tolerance of tomato and pepper specific herbicides applied through drip irrigation developed with the possibility that if herbicides injected under plastic were safe to pepper and tomato that further research could be conducted to develop systems that will manage nutsedge in pepper and tomato through application of herbicides through drip irrigation. Halosulfuron, imazosulfuron, and trifloxysulfuron were drip injected at three rates and post-directed at two rates. No tomato or pepper crop injury occurred during any of the growing seasons. Plant height did not differ between treatments. In 2007 and 2008, there were no differences between treatments for yield.
Publications
- Bangarwa, S. K., J. K. Norsworthy, and G. M. Griffith. 2010. Allyl isothiocyanate: A methyl bromide replacement in bell pepper. To be presented an the WSSA annual meeting.
- Bangarwa, S. K., J. K. Norsworthy, J. Still, G. M. Griffith, and L. E. Estorninos. 2009. Allyl isothiocyanate as a methyl bromide alternative in tomato. Proc. Weed Sci. Soc. Amer. 49:430.
- Bangarwa, S. K., J. K. Norsworthy, and G. M. Griffith. 2008. Phenyl isothiocyanate: A potential alternative of methyl bromide for weed control in tomato and bell pepper production systems. Proc. 5th International Weed Sci. Congress. 5:209.
- Bangarwa, S. K., and J. K. Norsworthy. 2008. Phenyl isothiocyanate as a methyl bromide alternative for weed control in tomato and bell pepper production. Proc. Weed Sci. Soc. Amer. 48:37.
- Bangarwa, S. K., J. K. Norsworthy, and G. M. Griffith. 2008. Phenyl isothiocyanate as an alternative of methyl bromide for weed control in tomato and bell pepper production. Proc. South. Weed Sci. Soc. Amer. 61:152.
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Progress 08/01/07 to 07/31/08
Outputs
OUTPUTS: A field experiment was conducted to evaluate the efficacy of Brassicaceae cover crops in converting glucosinolates to isothiocyanates, and their effect on weed suppression and crop injury. The major weed species evaluated were yellow nutsedge, Palmer amaranth, and large crabgrass. Eight different Brassica species, Indian mustard Fumus FE 75 and Fumus FL 71, canola Humus, brown mustard Southern Giant, turnip Seventop, herbcress, and a blend of white and brown mustard Caliante were drill seeded in mid-March. The cover crops were frequently irrigated and adequately fertilized with N, P, K, and S. The cover crops were mowed at 50% flowering stage by using flail mower. Cover crop samples were taken just before mowing from 1 m2 area for GSL content analysis. The plots were roto-tilled and covered with VIF mulch. Soil samples were taken from each beds under the plastic mulch for ITCs analysis at 7 different times up to 2 weeks . Tomato and bell pepper seedlings were transplanted one week after laying the plastic. Plots were rated for crop injury and weed control at biweekly intervals. Separate experiments were conducted to determine the optimum rate of allyl isothiocyanate for effective weed suppression using standard LDPE versus VIF mulch in AR. The major weed species evaluated in this test were yellow nutsedge, Palmer amaranth, and large crabgrass. The experiment consisted of two mulch type (LDPE versus VIF) and five different rates of ITC (0, 15, 75, 150, 750, and 1500 kg/ha). A standard methyl bromide plus chloropicrin at 390 kg/ha was also included for comparison. The ITC was applied using a backpack sprayer and immediately incorporated into the soil using a roto-tiller. Raised beds were prepared after ITC incorporation and covered with LDPE and VIF mulch. Tomato and bell pepper seedlings were transplanted three weeks after laying the plastic mulch. Transplant holes were punched in the plastic 48 hr before transplanting to aerate the beds. Crop injury and weed control were visually rated. Marketable fruits were harvested throughout the season and graded according to the USDA standards. In NC, studies in 2008 have been evaluating phenyl and methyl-isothiocyanate for weed control in pepper and tomato grown on LDPE or VIF mulch at various rates as well as herbicides for effective weed control in tomato and bell pepper. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: A report is being prepared for SEVEW (Southeastern Eastern Vegetable Extension Workers) so that the technology will be in the hands of the grower. This report will be mailed at the end of 2008 season to every extension worker who is a member of this committee and will be presented in the fall of 2009. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
No visual injury was observed in tomato, perhaps which is due to insensitivity of these crops to the allelochemicals released by the cover crops. No difference was observed among cover crops in terms of yellow nutsedge shoot penetration through the plastic. This may be due to the difficulty of yellow nutsedge shoots to penetrate the virtually impermeable film mulch. Weed control observations varied among and within cover crop plots, possibly due to variable stand and allelochemical production. The Southern Giant brown mustard and Fumus FE75 and Fumus FL71 Indian mustards provided the highest control of yellow nutsedge. Fumus FL71 Indian mustard and Seventop turnip were the most effective cover crops for controlling Palmer amaranth. Weed control began to rapidly decline soon after 2 wk following transplanting. In an additional experiment, allyl ITC at 750 kg/ha provided excellent control of purple and yellow nutsedge (>90%), Palmer amaranth (98%), and large crabgrass (99%). Tomato showed tolerance to allyl isothiocyanate at rates which provided effective weed control. Furthermore, tomato fruit yield was equivalent to methyl bromide. Overall, the virtually impermeable film mulch improved yellow nutsedge control over the low density polyethylene mulch. Disease resulted in loss of the bell pepper crop in 2008 in AR. In NC, it has been very difficult to inject isothiocyanates as they are relatively insoluble. In addition, the components of the injectors that are commonly used rapidly deteriorate when exposed to high rates of these isothiocyanates. This deterioration occurs as the product is being injected. Thus, rates of the isothiocyanates have been reduced. Additionally, tomato and bell pepper exhibits adequate tolerance to low rates of thifensulfuron-methyl. Thifensulfuron gives excellent control of common and pink purslane a persistent, difficult-to-control weed in tomato and pepper. A new registration for thifensulfuron was requested for tomato and residue tolerances are being developed through field studies by IR-4 field laboratories for an over-the-top application with a 45 day preharvest interval. Most of those field studies were completed in 2008.
Publications
- Bangarwa, S.K., J.K. Norsworthy, and G.A. Griffith. 2008. Phenyl isothiocyanate as an alternative of methyl bromide for weed control in tomato and bell pepper production. Proc. Southern Weed Sci. Soc. 61:152.
- Bangarwa, S.K., J.K. Norsworthy, and G.A. Griffith. 2008. Phenyl isothiocyanate a methyl bromide alternative for weed control in tomato and bell pepper production. Proc. Weed Sci. Soc. Amer. Abstract # 37. Available at: http://wssa.net/Meetings/WSSAAbstracts/abstractsearch.php
- Bangarwa, S.K., J.K. Norsworthy, and G.A. Griffith. 2008. Phenyl isothiocyanate: A potential alternative of methyl bromide for weed control in tomato and bell pepper production. Poster presented at 5th International Weed Sci. Congress, Vancouver, Canada, June 22-26, 2008.
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Progress 08/01/06 to 07/31/07
Outputs
OUTPUTS: Objective 1: Two Indian mustards, canola, brown mustard, turnip, and gardencress and a blend of Indian and white mustards were seeded in March 2007 and mechanically terminated in late spring. Cover crop root and shoot biomass production was determined. These samples will be analyzed for glucosinolates this fall. Flail-mowed plots were immediately rototilled and tarped with a virtually impermeable (VIF)mulch. Soil samples were collected from each plot at various intervals following maceration of the cover crop to quantify the conversion of glucosinolates to isothiocyanates (ITCs) and the longevity of ITCs in soil. Tomato and bell pepper were planted in the plots and tolerance of each crop periodically evaluated. Objective 2: The Brassica cover crops Seventop turnip, Pacific Gold mustard, and Calienta a blend of Indian and white mustards were drill seeded on March 13, 2007. The test area contained a natural infestation of yellow nutsedge, Palmer amaranth, johnsongrass, large
crabgrass, and broadleaf signalgrass. The cover crops were grown and incorporated in the same way as mentioned in the previous objective. The plots were covered with a low density polyethylene (LDPE) mulch or VIF mulch immediately after incorporating the cover crops. Tomato and bell pepper were transplanted one week after laying plastic. One half of each plot was kept weedfree while the other half was maintained as a weedy check. Tomatoes and bell pepper were harvested and graded according to USDA standards, but yield data has not been analyzed. Objective 3: Allyl ITC was used in place of 3-methylthiopropyl ITC due to the inavailability of the later ITC. Allyl and phenyl ITC were broadcast applied beneath two mulch films (LDPE and VIF) at five rates and compared with a standard rate of methyl bromide. Transplant holes were placed in the mulch 48 hours before transplanting tomato and bell pepper. Both crops were transplanted 3 weeks after applying the ITCs. Plots were rated for weed
control and crop tolerance, and fruit were harvested and graded. Results will be presented this winter at the Southern Weed Science Society and the Weed Science of America annual meetings.
PROJECT MODIFICATIONS: Allyl ITC was substituted for 3-methylthiopropyl in objective 3 due to difficulty in obtaining the later compound.
Impacts
Objective 1: Neither crop was negatively affected by any evaluated cover crop. Objective 2: No injury was observed in tomato and bell pepper. The VIF mulch was more than the standard LDPE mulch in preventing yellow nutsedge shoot penetration through the mulch. Objective 3: Unacceptable injury (>30%) was observed in tomato and bell pepper at the highest phenyl ITC rate of 1514 kg/ha. Phenyl ITC at 757 kg/ha provided tomato and bell pepper fruit yield equal to the standard methyl bromide treatment with minimal injury. Phenyl ITC at 757 kg/ha provided effective control of purple and yellow nutsedge (>80%), Palmer amaranth (95%), and grass species (85%) up to 8 weeks after transplanting. There was minimal or no injury to either crop from allyl ITC by 4 weeks after transplanting. Overall, allyl ITC was less injurious than phenyl ITC to both crops. Allyl ITC at 757 kg/ha provided tomato and bell pepper fruit yield equal to the standard methyl bromide treatment. Allyl ITC at
757 kg/ha controlled purple and yellow nutsedge >90%, Palmer amaranth 98%, and grass species 99% up to 8 weeks after transplanting. Overall, VIF film improved yellow nutsedge suppression.
Publications
- No publications reported this period
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