Observations from the field this week indicate that there are spider mite infestations at some level in most, if not all, peanut, cotton, and soybean fields in the drought-stressed Virginia regions. Drying of corn and weeds is contributing to this problem. Let’s all hope we get the rain we need to make a good crop this season. Rainy, humid weather will favor fugus that kills mites, but its effect may be mitigated by extremely hot conditions. Just in case, and since our last bad mite year was 2011, see below for a refresh about spider mites and how to treat them in each crop…
Concentrate on the field borders and look for the early signs of white stippling at the bases of the leaves. Do not confuse mite damage with dry weather injury, mineral deficiencies, and herbicide injury. Mite infestations will have some pattern, usually originating from field margins. Consider applying a miticide if more than 50 percent of the plants show stippling, yellowing, or defoliation over more than one-third of the leaves. Recommended products include Zeal and Agri-mek (other abamectin products are available, but not labeled for soybean). Lorsban and dimethoate are labeled and may require a second application. Bifenthrin will offer some suppression, but mite infestations will come back stronger.
Heavy infestations usually occur first around the borders of peanut fields; then they spread inward throughout the fields. Avoid harvesting spider mite infested cornfields or mowing weedy areas next to peanut fields until peanuts are harvested. Spider mites will readily move into peanuts when corn dries down or is harvested. Be prepared to treat peanuts if adjacent corn is infested. Use adequate pressure and GPA to ensure penetration of the canopy. Comite is our only registered product that works. See graph below from Dr. Mark Abney at UGA.
Mite damage first appears as a slight yellowing of the leaves, which later changes to a purplish or bronze color and is usually associated with webbing. Damage occurs especially in spots or on field edges but widespread defoliation is not uncommon if favorable conditions persist. I recommend abamectin (10 oz/A rate is usually sufficient) or Zeal for control. Bifenthrin, other pyrethoids, and especially acephate, will flair mites. If you are treating for plant bugs, I recommend Transform at 2-2.25 oz/A until wetter conditions prevail. Be mindful of the bollworm flight next week and do not make automatic sprays for worms until you confirm a problem in your field. Worm specific products (Prevathon, Intrepid Edge, Blackhawk) are better options than broad-spectrum insecticides (pyrethroids).
Our annual post-bloom survey starts next week. If you need help learning how to scout insect pests, call or text me on my mobile (919) 801-5366.