Avoid Insurance Applications of Insecticides in Corn and Soybeans - UNL CropWatch, July 18, 2013
July 18, 2013
Banks grass mites
Twospotted spider mites
We have received several reports of Banks grass mites in central and western Nebraska corn the last couple of weeks. This occurs as Banks grass mites move out of early spring hosts such as wheat, brome grass, or pastures. Depending on the stage of the corn when it is infested, the number of mites, and whether they are only in field edges or throughout the field, it may not pay to treat.
This week Paul Hay, UNL Extension Educator, Beatrice, reported several soybean fields with infestations of twospotted spider mites, usually on field borders.
Spider mite survival is often greatly reduced by the presence of several predatory insects and mites in both corn and soybeans. Given the projected hot, dry conditions for most of the state, conditions are favorable for spider mite growth.
As we move into July and August, growers may consider adding an insecticide with a herbicide or fungicide application as “insurance” against potential yield loss from insects. Unfortunately, most of these insecticides have broad activity against insects and mites, including those predatory species which feed on spider mites. There is a long history of mid-season foliar insecticide use resulting in increased spider mite populations later in the season in corn and soybeans, as well as other crops. Mid-season elimination of predatory and parasitic insects through insecticide applications also may encourage late-season survival of soybean aphids.
We do not recommend insurance applications of insecticides in the absence of economically damaging levels of insect pests. This is especially true in a dry summer, with spider mites already beginning to show up in Nebraska corn and soybeans.
See these 2012 CropWatch articles for more information:
Extension Entomologist, Lincoln
Extension Entomologist, Haskell Ag Lab, Concord