Spider mite populations increase under hot dry conditions and can cause economic damage in Missouri field crops. Several groups of insect predators effectively control spider mites. However, these natural enemies are more susceptible to insecticides, therefore, chemical control targeting early season pests such as Japanese beetles, may exasperate spider mite damage later in the season. Furthermore, imidacloprid applied as a systematic soil treatment or as a foliar spray can increase mite fecundity.
Spider mites are small (1/60 of an inch) and typically occur on the undersides of leaves making detection difficult. Identification can be accomplished using a 10-20 X hand lens. In soybean, chemical control is warranted when spider mites are present, and foliage yellowing reaches 20 % before pod set, or foliage yellowing reaches 10% after pod set. Most pesticides do not kill spider mite eggs, therefore additional applications are sometimes necessary 5 days after the initial treatment. Spider mites occur on numerous species of weeds along field borders. Weed control can reduce overwintering success and infestations in crops the following year.
REVISED: February 21, 2017