Follow Up Comments on Herbicide Resistance

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Original e-mail:

We are going to experience an explosion in PPO resistance in the next couple of years. My suggestion and I think this is a consensus among weed scientist is that growers should do everything in their power to keep escaped Palmer amaranth from seeding out. This is not a new recommendation but I think if folks don’t try hard on this in the next couple of years but most especially this year, we will be in trouble in peanuts and soybean. I am going to start recommending higher rates of paraquat in the peanut crop and maybe 2 applications based on the label. We have few alternatives that are effective. Residuals in addition to PPOs need to be emphasized (DNA and chloroacetamides) although we are already using those. Regardless, trying to get the escapes pulled that may be early populations of PPO resistant biotypes will be beyond critical and can’t be overemphasized. Don’t let anything seed out. It will pay in the long run.

Follow up:

  1. Lessons learned from glyphosate resistance include a field going from a few Palmer amaranth plants to the entire field in 3 years unless changes in management occur.
  2. With peanut we are rotating with cotton, corn, and milo so alternative chemistry can be used but soybean is in at least 25% of peanut rotations in NC. But we are using a large number of PPOs in peanut and they are fundamental for Palmer amaranth – flumioxazin (Valor SX and generics); sulfentrazone plus carfentrazone (Spartan Charge) (minimal use in peanut), acifluorfen (Ultra Blazer, Storm), and lactofen (Cobra). Carfentrazone (Aim) and pyraflufen ethyl (ET) are PPOs but these do not control Palmer amaranth (In fact because these burn Palmer amaranth some but do not control it and therefore may be increasing selection pressure for PPO resistance in a manner similar to spraying an effective herbicide like Cobra or Ultra Blazer to large weeds which results in poor control. There is evidence that this phenomenon hastens development of resistance.) Selection pressure is very high now in both peanut and soybean for PPO resistance.
  3. It is harder (and thus easier to ignore) to pull up escapes in soybean compared with peanut because of narrow rows, higher acreage in soybean for each farmer compared with peanut acreage for each farmer, and price. But a focus on having clean peanut fields by the end of the season is very doable. Do what you can in peanut for overall Palmer amaranth management (and other weeds) in a farming operation.

Article first appeared as North Carolina Peanut Note (PNNC-2015-103)