Jul 22, 2015

Watch out for spider mites in high tunnels in hot weather

In hot dry weather spider mite populations can spike quickly. Although the weather this summer has been far from dry, where high tunnels have protected from the frequent rains, spider mites have been a problem.

Spider mites cause stippling or bronzing of leaves as their feeding destroys the chlorophyll. At first glance it can be confused with nutritional problems. Heavily infested plants will have webbing on the undersides of leaves and sometimes between leaves. Crop losses occur when about 30% of the leaf surface is damaged.

Scouting

Don’t wait until damage is severe enough for you to see symptoms. A good way to detect mites is to tap the leaves over a sheet of white paper. When there are mites they will fall onto the paper looking like tiny moving dots. Use a good hand lens to view and identify the mites.

Two spotted spider mites have two distinct spots on their backs. Broad, cyclamen mites, and eriophyid are also mites to look out for.

Control

Phytoseiulus persimilis is a predatory mite which is a mainstay for spider mite control. They are active year round and feed on spider mite eggs, larvae, nymphs, and adults. They reproduce faster than the spider mites when temperatures are above 82F.

Neoseiulus californicus is another predatory mite. It can be used preventively because it can survive in the absence of prey. Start early to control spider mites with predator mites. If you have an active spider mite population introduce Phytoseiulus and Neoseiulus. Ultra vine horticultural oil and insecticidal soap are low residual toxicity pesticides that provide control with little impact on natural enemies.

See your most recent Commercial Vegetable Guide for mite sprays. For tomatoes Agri-Mek, Acramite 50WS, Portal, and Oberon 2SC are listed in 2015. Keep in mind, thorough spray coverage is important. These sprays are not compatible with a biological control program.

— Penn State University