Overuse can lead to resistance

2014_midvillefd_01sBob Kemerait opened a copy of the New York Times, Aug. 11, 2014, edition, reading the headline, “Invader Batters Rural America, Shrugging Off Herbicides,” as he talked to growers at the recent field day held at the Southeast Georgia Research and Education Center in Midville, Georgia. The article covers the glyphosate-resistant palmer amaranth and how farmers have overused glyphosate. The result, weeds with glyphosate-resisting genetic mutations.

Kemerait explains how glyphosate-resistant palmers first surfaced in the fall of 2004, in a field in Macon County, Georgia. The cotton farmer was concerned about the amount of pigweed that had survived in his field, though all other weeds seemed to be well-controlled with his herbicide program.  The grower contacted his then Extension agent, Jeremy Kichler, who worked with specialists at the University of Georgia to confirm that a glyphosate resistance issue was now a reality. Ten years later glyphosate-resistant Palmer Amaranth are present in at least 24 states.

Kemerait says the lesson learned from overusing glyphosate for weed control can be applied to peanut fungicides as well. Fungicides are critically important for controlling diseases in peanuts and farmers need to know and understand the fungicide’s chemistry, in addition to the brand name. In 2014, one commonly used fungicide to control soilborne diseases and foliar diseases, Abound, has become off patent. The active ingredient, azoxystrobin, is available to other companies now to develop generic formulations of the product. The best thing for growers with new generic formulations, Kemerait says, is the reduced price. However, Kemerait is concerned that the reduced price will lead to overuse and then to resistance problems, especially with leaf spot in peanuts.

At the Southeast Research and Education Center, Kemerait is working with county Extension agents, Mark Crosby of Emanuel County and Wade Parker of Jenkins County to review and compare the emerging arsenal of new fungicide and nematicide programs with older management programs. This work is critical given the recent generic status of azoxystrobin and new access to products such as Priaxor, Elatus and Velum Total.  Research data will be available following harvest comparing the fungicide chemistries and their performance on controlling diseases in peanuts.

View photos from the 2014 University of Georgia Southeast Research & Education Center in Midville, Georgia

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