Clean up two-spotted spider mites before fall

By Tina Smith, UMass Extension and Leanne Pundt, UConn Extension

It is important to clean up two-spotted mite infestations prior to fall to minimize infestations next spring.

Two-spotted spider mites (TSSM) multiply fast during warm temperatures and are common on greenhouse tomatoes, garden mums and on perennials. It takes about 28 days to develop from egg to adult at cool temperatures (50°-68°F)  but only about 8 days at 77°-95°F. For example at 60°F, one spider mite female can result in 20 mites after one month, at 70°F there will be about 12,000 mites and at 80°F 13 million mites. Since they can develop very quickly, it is important to monitor crops and treat early.

Do not allow infested weeds, unsold plants and greenhouse crops to remain in the greenhouse. The mites in your greenhouses now will be the same ones you will have on spring crops.

Two-spotted spider mites enter hibernation (diapause) in the fall when day-length shortens and evening temperatures drop. During diapause, the mites change color, turning orange to orange-red and walk off plants to hide in cracks and crevices in the greenhouse. As soon as temperatures are favorable in the spring, they slowly come out of diapause and move to the nearest plants. This is the reason that growers have a mite problem beginning in the same areas each year. In a diapause state, spider mites are more resistant to chemicals and are not as attractive to most beneficials. To reduce TSSM populations next spring be sure to clean up greenhouses and manage mites now. When removing infested plant material from greenhouses, be sure that cull piles are located far away from greenhouses as possible.