Location: Crop Protection and Management Research2012 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:
Cultivation is a proven component in the management of weeds in organic Vidalia sweet onion production. However, delays in the initial cultivation due to wet soils reduce the overall effectiveness of cultivation. In this case, improved performance using herbicides derived from natural sources would be useful. These herbicides were found to be much more efficacious when applied using a sprayer calibrated for a high output (>50 gal./A) compared to sprayers with a normal calibration (approximately 25 gal./A). When herbicides derived from natural products were applied in this manner, early season weed control was significantly improved and was synergistic with cultivation using a tine weeder. Research on multi-tactic approaches for effective glyphosate-resistant Palmer amaranth management continues. Winter cover crops rolled horizontal to form a thick mulch mat will help to hinder establishment of the small-seeded Palmer amaranth. Palmer amaranth populations in the southern United States have resistance to four different herbicide classes (mechanisms of action) and based on the genetic variability within the population, resistance to other herbicides is likely to already exist within a population. Repeated use of a particular herbicide class will select for this resistance, by allowing plants to establish and reproduce. Successful stewardship of the current herbicide technologies depends on minimizing the number of plants that are under herbicide selection pressure. The physical barrier of the rolled cover crop mulches reduces the established Palmer amaranth plant density. However, the mulch will bind some herbicides, keeping them from reaching the soil surface, reducing Palmer amaranth control. In addition, weeds that are able to emerge where the cover crop mulch was thin or moved during planting of the summer crop, may have greater growth than those growing without the cover crop. Research continues on ways to maximize consistent ground coverage of the mulch in order to minimize the safe sites for Palmer amaranth establishment.