Location: Crop Protection and Management Research
2017 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
Herbicide resistant Palmer amaranth (Amaranthus palmeri) is the dominant weed that affects management practices in agronomic crops of the southeast U.S. The small size of Palmer amaranth seed provides an opportunity to use physical weed control through high-biomass, rolled cover crop mulches as foundation cultural weed control practices to suppress weed emergence and lessen selection pressure on herbicides. While previously reported experiments by ARS scientists in Tifton, Georgia, demonstrated Palmer amaranth suppression in cotton by high residue rye planted no-till, other pests of cotton reduced yield compared to conventional tillage systems. No-till cotton production in high residue rye uses different herbicides than in conventional tillage production and while those herbicides control Palmer amaranth, annual grasses were not effectively controlled and reduced yield in continuous no-till cotton. Additionally, continuous no-till cotton production caused increased populations of plant parasitic nematodes to damaging densities and reduced cotton yield. In contrast, cotton grown in conventional tillage systems did not have losses due to nematodes. It is undeniable that Palmer amaranth growth is suppressed by high-residue cover crops and that no till system offers many advantages over conventional tillage systems. However, this crop production system must not substitute one pest complex for another equally damaging pest complex. It is clear that rotating crops is needed to lessen the selection pressure for other cotton pests and tillage should be periodically substituted into the cropping system to lessen development of other pest problems.
Accomplishments
1. Improved yellow nutsedge control in organic cropping systems. Perennial nutsedges are very difficult to control in organic cropping systems. Previous research conducted by ARS researchers in Tifton, Georgia, in cooperation with undergraduate mechanical engineering students at Auburn University, reported that a peanut digger with a custom-designed collection cart offers potential to collect and physically remove perennial nutsedges from organic fields. Research has continued to improve the prototype and develop a management system using this form of specialized perennial weed control. Presently, the best management system consists of two tillage operations at monthly intervals beginning in July during fallow periods. When operated during dry periods, two tillages with the peanut digger reduced yellow nutsedge densities by 73% the following season. Considering the baseline yellow nutsedge densities averaged 127 plants/m2, the performance of this specialized form of tillage is promising. However, it is clear that two fallow tillages for one season are not sufficient. Successful long-term suppression of perennial nutsedge populations requires specialized tillage repeated for multiple years.
2. Specialized implements improve in-row weed control in organic peanut. Although in-row weed control is difficult in organic peanut production, peanuts are very tolerant of aggressive early season cultivation. ARS researchers in Tifton, Georgia, demonstrated that in-row cultivation using rolling cultivators and finger weeders reduced smallflower morningglory densities by 95% and 94%, respectively, over the nontreated control and improved Texas millet control by similar amounts. Additionally, the rolling cultivator and finger weeder improved in-row smallflower morningglory control by 20% over the tine weeder. Aggressive cultivation with the rolling cultivator and finger weeder did not increase diseases in organic peanut, indicating excellent potential for this improved system of weed control.
3. Integrated systems of weed control using a tine weeder and herbicides. In conventional peanut production many herbicides are used that significantly add to the cost of peanut production and further the selection of herbicide resistant weeds. Previous research in organic peanut production identified the tine weeder as a versatile cultivation tool. ARS researchers in Tifton, Georgia, demonstrated that the integration of tine weeder cultivation with ethalfluralin, metolachlor, and imazapic improves control of four different weed species by an average of 16% compared to the same herbicides without cultivation. Additionally, yields when peanut were treated with herbicides plus cultivation were increased by 11% over herbicides alone. This form of integrated weed management is cost-effective and lessens selection pressure for herbicide resistance. This research has been expanded by evaluating the effects of different herbicide systems that target Palmer amaranth with cultivation over multiple sites and growing seasons.
Review Publications
Johnson, W.C., Davis, J.W. 2016. Effects of peanut stand uniformity and herbicide regime on weed management and yield. Peanut Science. 43:141-147.
Webster, T.M., Grey, T.L., Ferrell, J.A. 2017. Purple nutsedge (Cyperus rotundus) tuber production and viability is reduced by imazapic. Weed Science. 65:97-106.
