Spider mites (specially the two-spotted spider mite, Tetranychus urticae) is a regular occurrence in many row crops of Alabama. The 2016 drought really provided the perfect conditions for spider mites in peanuts, especially those treated with synthetic pyrethroids for managing mid-season insects like caterpillars.
Once you get spider mites in peanuts, there is only one registered chemical class. The recent US Drought Monitor has started to show some areas of abnormal dryness – so stay alert and watch the drought monitor.
This article summarizes our first-year spider mite research in peanuts where we deliberately used a synthetic pyrethroid to flare up the pest. This research was done under a high tunnel in Clanton in order to exclude rainfall (rains have ruined many of our studies in the past).
Peanuts were treated with bifenthrin on August 1 and 15 at 6 oz per acre; these chemical treatments killed beneficial mites and aggravated the two-spotted spider mite to invade the crop. After about 10 days post-treatment, we had a terrible outbreak of spider mites that was shocking to the eye.
Within 15 days post-treatment, spider mites started to aggregate in large numbers on the leaf terminals and the plants were severely webbed (picture below).
Interestingly, another species of spider mites, Tetranychus tumidellus, was found at Brewton last year. T. tumidellus has red body and flared up in one area of the field, but never did as much damage as T. urticae. So, if producers see anything interesting like this, then please take a picture as best as you can and contact a regional extension agent so we can document cases.
In 2016, we tested two unregistered miticides, Agri-Mek and Portal, with the hope that the industry may be interested to register them in peanuts in future (there is a IR-4 proposal in the making).
Comite was the registered miticide for comparing effectiveness of spider mite control. Split or single application of Portal and Agri-Mek significantly reduced two-spotted spider mites compared to the untreated check; the products also had good persistence in controlling mites (picture below).
When seen under a microscope, dead spider mites are visible as shriveled bodies compared to mite samples from untreated plots. Overall, we were able to show from this study that spider mites alone can cause 29% yield loss in peanuts under stressful environmental conditions.
In conclusion, peanut producers should pay very close attention to insecticide rotation and use some of the new softer or more selective insecticides for caterpillar control to prevent spider mite outbreak.
Selective insecticides are also safer to beneficial insects that feed on caterpillars and other pest species. Irrigation in peanuts is also helpful to reduce some foliar and soil insect pests.
There are many choices for pest management when insects/mites are detected early and treated timely; call a regional extension agent or go online for the Peanut IPM Guide for developing an IPM plan suitable for your farm. For contacting the author (Dr. A), call or text 251-331-8416.