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Title: Herbicide Resistant Weeds: Do Economic Thresholds Still Have a Role in Weed Management?

Author
item WILKERSON, G - NORTH CAROLINA STATE
item LASSITER, B - NORTH CAROLINA STATE
item JORDAN, D - NORTH CAROLINA STATE
item WILES, LORI

Submitted to: International Weed Science Congress
Publication Type: Abstract Only
Publication Acceptance Date: 2/22/2008
Publication Date: 6/23/2008
Citation: Wilkerson, G.G., Lassiter, B.R., Jordan, D.L., Wiles, L. 2008. Herbicide Resistant Weeds: Do Economic Thresholds Still Have a Role in Weed Management?. International Weed Science Congress.June 23-27,2008

Interpretive Summary:

Technical Abstract: Concern over the development of herbicide resistant weeds has prompted a closer look at the validity of using economic thresholds (ET) as a basis for making treatment decisions. In situations where herbicide resistance is suspected, growers are often advised to employ control measures to completely eradicate the weed from the field, in order to eliminate seed production. The decision aids HADSS (Herbicide Application Decision Support System) and WeedSite utilize the concept of ET in order to recommend appropriate herbicides for use in a particular crop. The decision aids makes recommendations using specific parameters for yield, crop value, and weed competitiveness. These programs could aid growers in determining specific herbicides to attain high levels of weed control as well as high returns within a specific cropping system. Existing weed scouting data from over 200 Arachis hypogaea L. (peanut), Glycine max (L.) Merr. (soybean), Gossypium hirsutum L. (cotton) and Zea mays L. (corn) fields were used in combination with either HADSS or WeedSite to compare efficacy and net returns for different management strategies, assuming either no herbicide-resistant weeds, or one resistant weed species in each field. G. max, Z. mays, and G. hirsutum fields were assumed to have been planted with a glyphosate-resistant cultivar. Data were used to estimate yield loss, weed densities, and net return after treatment for each field under differing assumptions of herbicide resistance. Results indicate that the impact of a resistant weed species on herbicide selection, net return, and yield loss varies considerably from field to field and is affected by crop, the identities and densities of all weed species present in the field, and available herbicide options. In general, the presence of a resistant weed species decreases net return, whether decisions are made based on optimizing net return, minimizing yield loss, or minimizing density of the resistant weed. In some situations, no treatment with maximum efficacy against the resistant weed provided adequate control of the other weed species present in the field. ET models may require modification to include additional herbicide combinations or to allow evaluation of spot treatments following whole-field treatments. With some modification, these models can be used to assist decision makers in evaluating the costs and potential benefits of various resistance management strategies.