Irrigation, Spider Mites and Leaf Spot Peanut Notes No. 222 2022

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I had a question about how to handle a field with center pivot irrigation and the areas around the pivot that are dry with spider mites. My recommendation was to spray the pivot area for leaf spot (the farmer was planning to spray chlorothalonil plus tebuconazole across the entire field, initially) but not to spray the dry area. There was no sign of leaf spot in the dry area (lesions) and there was a considerable number of mites. We know chlorothalonil (and other fungicides) can flare mites. Mites are not generally an issue under moist and humid conditions because a pathogen is detrimental to mites. Under dry conditions when the mite populations build, the pathogen is at a low level. If we apply a fungicide under these conditions, we essentially knock out the pathogen and mite populations will build even faster.

The farmer was debating about spraying a miticide with 2-3 weeks remaining before digging for the dry peanuts. Several options are available, and Rick (Brandenburg) has excellent information in 2022 Peanut Information about the strengths and weaknesses of various approaches. The grower is most likely going to spray bifenthrin. This product can suppress adults and just might do well enough with the time remaining in the season. It is much less expensive than Portal, although Portal controls adults and eggs and would be considered a longer-term solution. Regardless, the cooler temperatures we will experience in the next week will slow mites down.