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United States Department of Agriculture

Agricultural Research Service


Location: Crop Protection and Management Research

2011 Annual Report

1a. Objectives (from AD-416)
1. Develop integrated systems of weed management for organic agronomic and vegetable cropping systems, such as peanut, cotton, cucurbits and dry bulb onion respectively, in the southeastern coastal plain. 2. Identify the ecological and edaphic factors affecting the reproduction, spread, and survival of invasive, herbicide-reistant, and herbicide tolerant weed pests of agronomic and vegetable crops in the southeastern coastal plain, including, but not limited to pigweeds, common bermudagrass, and perennial nutsedges. 3. Combine effective chemical and cultural control measures into integrated systems for the management of key species of herbicide resistant and invasive weeds of agronomic and vegetable crops in the southeastern coastal plain, such as pigweeds and Benghal dayflower.

1b. Approach (from AD-416)
Research will be conducted to determine weed management practices that will: A) Manage weeds without conventional herbicides in organic systems and B) reduce reliance on a dwindling number of herbicide tools in conventional systems. Conventional weed management systems rely heavily on herbicides to minimize crop yield losses associated with weeds. Organic cropping systems have few approved herbicide options, and must rely primarily on weed control from cultural and mechanical practices. The occurrence of herbicide-resistant weeds has limited the efficiency of many herbicides in conventional systems. Studies will be initiated to evaluate a multi-tactic approach to managing weeds with a reduced reliance on herbicide tools. In the first objective, integrated weed management systems will be developed in organic agronomic and vegetable cropping systems. Cultural and mechanical weed management strategies will be employed to prevent seedling establishment and reduce propagule persistence in the soil. The second objective will determine the factors that affect the reproduction and persistence of herbicide-resistant and herbicide tolerant weed pests. Specific studies will include the effect of cover crops on weed establishment, growth, and fecundity, as well as determining the factors that affect persistence of the soil seedbank. The third objective is to combine effective chemical and cultural control measures into integrated systems for the management of key weed species. Weed growth and reproduction as affected by crop stand and presence of cover crops will be evaluated. Ultimately fulfillment of these objectives will improve grower profitability and reduce reliance on a limited set of herbicide resources that are rapidly declining in efficiency.

3. Progress Report
Mechanical weed control with cultivation using a tine weeder has been a consistently effective tactic in organic peanut production, based on previous research and on-farm validations. Despite the effectiveness of intensive cultivation, weed control in the row remains problematic. In preliminary trials, periodic early-season cultivation with a tine weeder operated perpendicular to row direction improved weed control in the row of organic peanut over cultivation solely parallel to row direction. Furthermore, peanut injury and stand losses were surprisingly minimal from perpendicular cultivation. This unique method of cultivation greatly improved weed control in organic peanut production, without any increase in cost of production.

4. Accomplishments
1. Palmer amaranth seed longevity less than 40% after two years. Palmer amaranth with resistance to glyphosate (trade name Roundup, among others) was first detected in Georgia, but has spread throughout the southern U.S. The longevity of this small-seeded annual species in the soil seedbank will regulate the population dynamics in growers’ fields. ARS Researchers in Tifton, GA assessed Palmer amaranth seed longevity in soil burial studies. Across three soil depths, seed viability was reduced at least 20, 40, and 60% after 6, 12, and 24 months, respectively. The relatively rapid decline of seed viability at shallow soil depths may allow growers to rapidly alter their weed populations if weed seed production is prevented. As herbicide resistance continues to develop in Palmer amaranth (currently resistant to four herbicide mechanism of action), leveraging the inherent strengths of agroecosystems will garner increased significance in management of this species and others.

2. Alternatives to conventional polyethylene mulches. Most commercial vegetable production in the southeast uses transplants grown on seedbeds covered with thin-film mulch. It is costly to procure, remove from the field, and dispose thin-film mulches. Alternative biodegradable mulching materials will eliminate the cost associated with removal and disposal. In preliminary trials, ARS researchers in Tifton, GA evaluated an alternative mulching material made from processed cotton gin trash. This material was successfully applied using conventional mulch application equipment and adequately suppressed weeds when treated post-application with linseed oil, black latex paint, or dark-colored paint derived from natural plant-based products. The rolled cotton fiber mat made from cotton gin trash offers great potential as an alternative mulching material since it is fully biodegradable, made from a common waste material, and serves as a value-added product to the cotton industry.

3. Organic herbicides and cultivation for weed control in organic peanut and sweet onion production. Herbicides derived from natural sources may be used in certified organic crop production. However, little credible information is available regarding weed control efficacy and crop safety of these herbicides. ARS researchers in Tifton, GA examined various herbicides derived from clove oil, d-limonene, and lemongrass oil in organic peanut and Vidalia® sweet onion production, in conjunction with intensive cultivation with a tine weeder. Naturally derived herbicides improved overall broadleaf weed control in organic peanut production, but only when used in conjunction with intensive cultivation. Banded applications of these herbicides reduce herbicide costs. The value of these herbicides in Vidalia® sweet onion production was limited due to poor control of cool-season weeds.

4. Eradication of napiergrass, a potential biofuel crop, poses challenges. Napiergrass is a high biomass perennial grass that has been identified as a potential biofuel crop for the southeast U.S. Eradication protocols have not been developed to rapidly respond to escaped plants, reclaim abandoned production fields, or facilitate rotation to other crops. ARS researchers in Tifton, GA examined napiergrass response to herbicides in greenhouse and field studies. Carbon dioxide assimilation in napiergrass was halted by herbicides (i.e. they were effective) in greenhouse studies, however, sequential herbicide applications failed to eradicate established field populations. As glyphosate (trade name Roundup, among others) was ineffective at the rates and frequencies tested, eradication strategies are still elusive, but necessary, in order to assist in containment and transition to the next crop.

5. Cultivation is crucial for weed control in organic sweet onions. Consumer demand for certified organic Vidalia onion is high; however weed management is difficult. ARS researchers in Tifton, GA conducted trials to evaluate an integrated system of solarization, cultivation, and organic herbicides for weed management in organic onion production. Of the three weed control options, cultivation with a tine weeder was the most effective tactic in transplanted Vidalia onion production and significantly reduced the cost of weed control compared to handweeding. Cultivation organic Vidalia sweet onion with a tine weeder saves organic onion growers $1,400/A compared to large-scale use of costly handweeding.

6. Non-chemical methods for perennial weed control. Common bermudagrass is a troublesome perennial grass common in the southeastern U.S. and extremely difficult to control in organic crop production systems. Sites commonly used for transition to certified organic crop production are frequently infested with common bermudagrass. ARS researchers in Tifton, GA initiated trials in a site heavily infested with common bermudagrass to evaluate systems of perennial weed control during fallow organic transition. Treatments included all possible combinations of two primary tillage implements (power spader, disk harrow), summer weed control (solarization, fallow tillage with a peanut digger, and non-treated control), and winter tillage (fallow tillage with a peanut digger and non-tilled control). Common bermudagrass densities were reduced by combinations of summer solarization or summer tillage with a peanut digger, followed by winter tillage with a peanut digger. The peanut digger displaced common bermudagrass and exposed the vegetative material to desiccation. However, control was not sufficient enough to prevent re-infestation by survivors when implemented for only one season and must be repeated to achieve maximum benefit. When properly implemented, these systems of weed management are the only method of perennial weed management in organic transition. Failure to control perennial weeds in organic transition will force abandonment of organic crop production sites due to perennial weed competition and reduce the number of certified organic farms.

7. Crop row spacing and cultivation are critical for weed control in organic peanut. Weed control is a limiting factor for organic peanut production. ARS researchers in Tifton, GA found techniques of weed management that offered promise in organic peanut production. Cultivation with a tine weeder effectively controlled weeds when peanut were seeded at a density of 20 seed/m. In contrast, if peanut were seeded in multiple rows at 10 seed/m, then weeds were not controlled using any cultivation regime. The most effective cultivation regimes began just prior to peanut emergence. Organic peanut growers have utilized this knowledge to successfully control weeds in their production systems.

8. Seasonality of Palmer amaranth seed herbivory. Palmer amaranth is the most troublesome cotton weed in Arkansas, Georgia, Missouri, North Carolina, and South Carolina, with the capability of producing up to 600,000 seeds per plant. Following seed dispersal from the mother plant, Palmer amaranth seed on the soil surface can be returned to the soil seedbank or consumed by herbivores. ARS Researchers in Tifton, GA deployed seed filled traps over multiple years to evaluate if and when seeds are consumed. Seed traps that excluded large arthropods and rodents had 56 to 66% seed removal, while open traps had 75% removal. Peak seed removal occurred in late summer and autumn, with less frequent removal in winter and spring. The lack of effective herbicides for control of Palmer amaranth increases the importance of implementing measure to reduce the population density of this species in an effort to improve weed management. Even with the small size of these seeds, herbivores sought out the seed. Post-harvest management treatments that disturb the soil surface and incorporate seed into the soil seedbank should be delayed to maximize seed herbivory.

9. Autumn disturbance hinders establishment of cutleaf evening-primrose. Conservation tillage reduces soil erosion, but allows cutleaf evening-primrose, an autumn germinating weed to overwinter and cause problems the following spring. Primrose that tolerates spring applications of glyphosate and the large rosettes interfere with planting and also harbor pests. Timely autumn treatments following cotton harvest (around November 1) reduced primrose populations the following spring. While inclusion of 2,4-D with spring-applied glyphosate effectively controls primrose, hindering weed establishment in the autumn avoids restrictions on planting times and could potentially be beneficial in resistance management rotations once 2,4-D-resistant crops become commercial.

Review Publications
Cutts, G., Grey, T., Vencill, W., Webster, T.M., Lee, R., Tubbs, R., Anderson, W.F. 2011. Herbicide Effect on Napiergrass (Pennisetum purpureum Schum.) Control. Weed Science. 59(2):255-262.

Timper, P., Davis, R.F., Webster, T.M., Brenneman, T., Meyer, S.L., Zasada, I.A., Cai, G., Rice, C. 2011. Response of root-knot nematodes and Palmer amaranth to tillage and rye green manure. Agronomy Journal. 103(3):813-821.

Culpepper, A.S., Webster, T.M., Sosnoskie, L.M., York, A.C. 2010. Glyphosate-resistant Palmer Amaranth in the U.S. In: Nandula, V.K., editor. Glyphosate Resistance in Crops and Weeds History, Development, and Management. Hoboken, NJ: John Wiley & Sons, Inc. p. 195-212.

Johnson, W.C., Prostko, E., Davis, J. 2011. Phytotoxicity of Delayed Applications of Dinitroaniline Herbicides in Strip-Tillage Peanut Production. Peanut Science. 38:57-60.

Last Modified: 06/22/2017
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