Field infestations have been reported from the southern high plains to the northern panhandle. When we begin talking about spider mites it is usually about infestations on corn. The two most common species are the Banks grass mite and the twospotted spider mites. Their biology, life cycle, feeding damage is the same on sorghum as it is corn.
Mites begin on the underside of the leaf in the lower portion of the sorghum canopy. As populations increase feeding damages a greater portion of the leaf area and can kill entire leaves. Control decisions should be considered when 30 percent of the leaf area of most sorghum plants in a field show some damage symptoms from mite feeding. Only two acaricides (Comite II and Onager) are registered for spider mite control on grain sorghum.
For Comite II the application rate is between 24 and 36 fl. oz. per acre. The recommended application volume for ground application is a minimum 20 gpa and aerial application a minimum 5 gpa. Only 1 application per season is permitted. Comite II is phytotoxic to some sorghums and the pre-harvest interval is 30 days for silage and 60 days for grain.
The use rate for Onager is between 10 and 24 fl. oz. per acre. Ground application is recommended at 15 to 20 gpa and a minimum of 5 gpa for air application. Only 1 application per season and the total amount per season is 24 fl. oz. per acre. The pre-harvest interval is 30 days. There is no distinction on the label for grain or silage pre-harvest interval.
Just as for corn, spray coverage is extremely important to the performance of these two acaricides. So the minimum application volume should be used. Applications of pyrethroid insecticides for headworms, stinkbugs, and sorghum midge will also flare spider mite populations by removing natural predators.
Applications of chlorpyrifos or dimethoate for aphid control may provide an initial knockdown of spider mites. But populations can resurge because only adult and immature spider mites are killed, leaving the eggs for immatures to hatch out. Also, these two insecticides will eliminate the natural predators.