No Rain but Humid Peanut Notes No. 150 2020

— Written By

Some areas of the state have turned dry over the past three weeks. Lack of rain does not mean conditions in the peanut canopy are not favorable for leaf spot development. While it may be attractive to delay a fungicide application, we encourage you to take a look at the leaf spot advisory system Dr. Shew has in place. This is a good indicator of whether or not conditions are favorable for this disease to develop. The advisory can in many cases help us eliminate a fungicide spray or two when conditions are indeed dry (no rain and low dew points,) but the advisory can help us keep spraying when conditions are favorable even though rain may be limited or not occurring at all but dew points allow the pathogen to develop.

We generally apply chlorothalonil early in the season. Keep in mind that if this fungicide is a major component of our disease management program, under dry conditions we can flare spider mites. For this reason look closely at the fungicide options we have in place and use those that are effective on leaf spot (if dry but high enough dew points for disease development – see a local advisory recommendation) but have less risk flaring spider mites (most fungicides have at least some capacity to do this but chlorothalonil is particularly good at doing this.)