Fungicide Resistance Management

— Written By

Barbara sent me an excellent note reminding us all of how important resistance management is with fungicides. We all know what happened with glyphosate…we have lost broad utility and herbicide programs have gotten much more difficult and expensive because of that stewardship. If you look around most peanut fields they are very clean from a disease standpoint. This is in part because of good rotations and better variety resistance but is also because of the excellent fungicide programs we have in place. So, if we want to keep these in place and benefit from performance on these products we need to be good stewards. Take a good look the disease chapter and see how to appropriately manage resistance. For example, look at the comments on Headline use. My recommendation on late-season Headline use is very effective in the short term but maybe not in the long term. While chlorothalonil will help form a resistance standpoint, the Headline is more persistent than chlorothalonil, so it will last a week longer meaning the Headline would be susceptible to resistance development because the chlorothalonil will have played out more quickly. I spoke to one farmer Thursday that had just applied 12 oz Headline/acre as his last spray. I have no doubt that this will do an excellent job right here at the end of the season, but the concern is long-term resistance. We need to make sure chlorothalonil is applied in a manner that outlasts the chemistry that is vulnerable to resistance. And, we need to rotate often in the season with fungicides with different MOAs. There was some resistance for worms to the pyrethroids. While not widespread, we also need to be good stewards there as well. Same thing with herbicides.

Our long rotations give us some flexibility in that we are not growing peanuts every year and many of our rotation crops do generally not need some of the fungicides. But, with higher grain and cotton prices and aggressive salesmanship, fungicides, and for example Headline, are being sprayed on corn and wheat and perhaps others on a pretty wide scale. This can only increase the susceptibility to resistance.

I am not an alarmist, but in the early 2000s we felt like we were home free from a weed control standpoint in cotton and soybeans with glyphosate…everything looked easy and fields were really getting cleaned up and crop yields optimized (except maybe early season weed interference because we did not use PRE herbicides and because we could rely on glyphosate to kill big escapes.) We have to ask ourselves if this is the case with peanut fungicides…we have lessons on resistance from other crops and chemistries; we just need to listen to those lessons and be proactive.With all that said, my salvage treatment in my test with Headline plus chlorothalonil puts us at risk…so I know the three fingers are pointing back at me with one pointed at everyone else. Most of you remember the “monster field” (C11 at Rocky Mount that I created with respect to ALS resistant common ragweed and Palmer and now glyphosate resistant Palmer…real ugly situation!) Do as I say and not as I do…

Article first appeared as North Carolina Peanut Note (PNNC-2011-053)