Maintaining Fungicides for the Long Run Peanut Notes No. 189 2020

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We have had some places where growers and their consultants think they are seeing leaf spot disease. Barbara and I have looked at images for some of these cases and it looks like the issue is not the traditional leaf spot we control with fungicides (see Peanut Notes No. 187.)  With that said, growers are spraying to make sure leaf spot does not cause major issues and one of the options is Miravis. We recommend that this fungicide be applied earlier in the season and not as a late-season option, especially as the last spray. Below is correspondence with a consultant from Dr. Shew and I about late-season sprays of Miravis.

Jordan:

Promise me you will encourage (perhaps mandate) that your farmers spray chlorothalonil in 3 weeks, after Miravis, and before you dig. I don’t think it is too big of an exaggeration, but the longer interval of control provided by Miravis is a game changer for some farmers, especially those with large operations. Being able to walk away from a field for almost a month with good leaf spot control is a good opportunity. BUT, this product may not last long if it is sprayed toward the end of the season without a follow up using an effective resistance management fungicide. There will be a lot of data showing that this might be all you need. It looks great. But so did glyphosate for about 5 years. And then it fell apart on some weeds. Headline was also fantastic and it is now ineffective in most cases. We also failed to protect Folicur in the early days because it was so good. Now it is ineffective. Abound is ineffective in most cases at this point. We need to protect what we have left.

Shew:

I am pretty concerned about the long-term viability of the Syngenta two spray program, assuming this means two applications of Miravis (with or without Elatus) per year. In my view, two applications in this scenario is equivalent to *four* applications of an unmixed selective a.i. That is, using the same a.i. for 8 weeks out of the season is like using a QoI or DMI 4 times. This is far outside of FRAC guidelines for resistance management given the total number of sprays applied in our area and has already proven to be very risky based on our experience with QoIs and Folicur. I understand the convenience to the grower but don’t feel it’s worth the long-term risk.

I appreciate your continuing efforts in helping growers make good choices. Anything that you can do to counteract other information growers hear will benefit everyone in the long run.