Location: Crop Protection and Management Research
2019 Annual Report
Objectives
Objective 1: Identify the ecological and edaphic factors affecting the dynamics of invasive weed pests, especially perennial weeds and weeds of cool season crops, in the southeastern United States. Develop management tactics that effectively disrupt the relationship between bacterial diseases and weed hosts, such as occurs in organic onion production.
Sub-objective 1.A. Characterize weed phenology as it occurs under various cultural practices in an effort to develop management tactics that effectively disrupt weed establishment.
Sub-objective 1.B. Improve perennial weed management by targeting production and persistence of vegetative propagules.
Sub-objective 1.C. Determine if improved in-row weed control in organic peanut production can be improved by planting in a depressed seedbed and aggressive cultivation, without compromising disease management.
Objective 2: Improve cultural weed control strategies, including conservation tillage methods that can be used as part of integrated weed management systems for invasive and herbicide resistant weeds. Improve cover crop mulching systems in cotton that are used to control glyphosate-resistant Palmer amaranth, such that they also better control other common, problematic weeds.
Sub-objective 2.A. Evaluate the influence of various edaphic factors on weed seed persistence in the soil seedbank.
Sub-objective 2.B. Determine the effect of high-biomass cover crop mulches on glyphosate-resistant Palmer amaranth growth.
Subobjective 2.C. Determine when viable Palmer amaranth seed production first occurs and characterize the timing of seed dispersal from the female plant during the growing season.
Approach
Research will be conducted in conventional and organic summer and winter crops in the southeastern coastal plain to develop weed management practices that utilize diverse tactics to minimize herbicide reliance.
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, the factors that affect the dynamics of problematic weeds in conventional and organic systems, especially weeds of cool-season crops (e.g. Vidalia onion and sugar beet) and perennial weeds, will be characterized. The impact of the timing of control practices on weed establishment will be evaluated. Management practices that reduce vegetative propagules of problematic weeds will also be studied. The second objective will evaluate integrated diverse weed control tactics of herbicide-resistant weeds. The influence of rolled high-biomass cover crops and nitrogen management on weed seed persistence in the field soil seedbank will be determined. Herbicide-resistant weeds thrive in the current herbicide-dominated weed control systems, with selection pressure for herbicide-resistant weeds. These studies will address if there are additional management practices that can be altered to improve weed control and alter the selection pressures on weeds. The ultimate goal of these objectives is to improve grower profitability and reduce reliance on a limited set of herbicide resources that are rapidly declining in efficiency.
Progress Report
Organic peanut production is a high-risk cropping system, largely due to difficulties in managing weeds using methods acceptable for certified-organic production. In contrast with conventional peanut production that relies heavily on synthetic herbicides, organic peanut production must use an integrated system to manage weeds. The foundation for an integrated weed management system is cultural weed control which is a system of production practices that promote uniform peanut growth to suppress weeds. Cultural weed control includes practices that promote vigorous early-season peanut growth and lessen chances for weed escapes. Mechanical weed control is based on repeated cultivation using a tine weeder and sweep cultivator to control weeds before they emerge. However, weed control consistency from cultivation is affected by rainfall that can delay scheduled cultivations and hinder implement function. Herbicides derived from natural products and thermal weed control using propane flaming have limited value in organic peanut production due to limited weed control spectra, specifically poor control of annual grasses and perennial weeds. Successful weed management in certified organic peanut production will depend on an integrated system, not a single form of weed control.
Accomplishments
Review Publications
Johnson, W.C., Webster, T.M., Grey, T.L., Luo, X. 2018. Cultivation and reduced-rate herbicides for cost-effective weed control in sugarbeet grown for biofuel. Weed Technology. 32(6):726-732. https://doi.org/10.1017/wet.2018.61.
Johnson, W.C., Luo, X. 2019. Integrating cultivation using a tine weeder with herbicides in conventional peanut production. Weed Technology. 33(2):374-379. https://doi.org/10.1017/wet.2018.114.
Johnson, W.C. 2019. A review of weed management challenges in organic peanut production. Peanut Science. 46(1):56-66. https://doi.org/10.3146/PS18-12.1.
