2007 Managing Glyphosate-Resistant Palmer Amaranth Roundtable Presentations

EXECUTIVE SUMMARY

Confirmed, resistant populations of Palmer amaranth are found in Arkansas, Georgia, North Carolina, South Carolina, and Tennessee. Palmer amaranth populations suspected of being glyphosate-resistant are being investigated in other Southern states. Glyphosate, used in conjunction with glyphosate-resistant cultivars, provides flexible and reliable broad-spectrum weed management in cotton and soybean. A general distribution of glyphosate-resistant Palmer amaranth would significantly increase the cost and difficulty of weed management in these crops. Weed scientists in the Southeast and Mid-South are trying to develop effective management programs, generally incorporating increased use of preemergence herbicides. Glyphosate-resistant Palmer amaranth is viewed as a potentially serious threat to the continued use of conservation tillage, although effective use of cover crops may provide a possible means of combating this pest. Much remains to be known about the ecology, physiology and genetics of the resistance. One need is a method to unambiguously express the intensity of resistance in a manner that is consistent among populations. Greater understanding of the biology of the resistance would assist applied researchers to develop better management strategies. Cost effective management strategies are urgently needed, as is an industry consensus that resistance management considerations are a requisite component of herbicide use.

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AGENDA

Problem: Palmer amaranth (Amaranthus palmeri) has been a management problem for several years in both cotton and soybean cropping systems, especially since the expansion of conservation-tillage practices. Glyphosate-resistant populations of Palmer amaranth are now found in several counties in five different states. Most researchers and producers agree that resistance in this weed species is a significant concern and will have considerable economic impact in areas where it becomes established. With more acres at risk in 2008, a united effort by researchers, herbicide manufacturers, and commodity groups is imperative to find effective management options for glyphosate-resistant Palmer amaranth and to attempt to limit its rate of spread.

Objective: The meeting was organized to bring together individuals involved in Palmer amaranth management to exchange ideas and coordinate research and educational efforts for maximum advantage.

Protocol: Approximately 35 attendees, from research/extension, the herbicide industry, and the cotton and soybean commodity organizations, shared their experiences with glyphosate-resistant Palmer amaranth with informal presentations and a roundtable discussion. Attendees were from several mid-south, south, and southeast states including North Carolina, Georgia, South Carolina, Mississippi, Tennessee, and Arkansas, and from Missouri and Colorado.

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