Early confirmation of twospotted spider mite
There are not established economic thresholds for twospotted spider mites in corn and soybean, but scouting for initial infestations is very important to avoid yield loss. Twospotted spider mite is capable of reducing soybean yield by 40 to 60 percent when left untreated; drought-stressed plants could experience even more yield loss.
click image to zoomPhoto 3. Foliar insecticide treatments should be made to fields before prolonged spider mite feeding causes yellowing or leaf drop. Photo taken by Tracy Cameron on June 6, 2012, in Richardson County, Neb. Organophosphates are the recommended insecticidal chemistry for twospotted spider mite control. Examples include dimethoate and chlorpyrifos. These products may not kill the eggs, thus a treated field should be scouted 7 to 10 days after application to determine if a second application is necessary. As always, refer to the label for the appropriate rates and re-entry intervals. Pyrethroid insecticides should not be used to control twospotted spider mites as they are not as effective and can actually flare populations. Under dry conditions, foliar treatments are recommended when plants have substantial stippling or leaf-yellowing and spider mites are active (Photo 3). Because a naturally-occurring fungus can control populations, treatment of twospotted spider mites may not be required when temperatures drop below 85°F and humidity levels are greater than 90 percent for an extended time. Mites that are infected by the fungus will appear brown and will not move on the piece of paper used for scouting.