Issue 7, July 16, 2021

Twospotted Spider Mites

Twospotted spider mite (Tetranychus urticae), Frank Peairs, Colorado State University, Bugwood.org

Twospotted spider mites (Tetranychus urticae) are herbivorous mites that feed on a broad range of deciduous trees and broadleaf evergreens. In cool or damp weather their populations are controlled naturally by fungi and other pathogens. However, their populations flourish in hot, dry conditions.
Spidermites suck fluids from plants causing yellow speckling on the surface of the leaves called stippling. This can make some leaves look yellow or bronze at a distance. Spider mites also leave fine silk between the leaves and petioles. Heavy infestations can kill plants over time.
When scouting for mites, it’s important to identify whether you have predatory or herbivorous mites before applying a treatment.  The easiest way to do this is to collect mites onto a sheet of paper and inspect them. 

Hold a piece of white paper under a branch and hit the branch with a rake handle.  This should knock the mites onto the paper, where they can be seen more easily.  Red mites are predatory mites that feed on herbivorous mites.  If you find many red mites, don’t apply a treatment because it will kill the predators.  Green mites are herbivorous mites, feeding on the plant. If you find many green mites and have significant injury, you can apply a treatment to control them.  The treatment must be applied when mites are active and present on the tree.

Left: Spruce spider mite, USDA Forest Service - Northeastern Area, USDA Forest Service, Bugwood.org
Right: Spider mite, Eric Coombs, Oregon Department of Agriculture, Bugwood.org

When controlling mites, be sure that mites are indicated on the pesticide label, because products labeled for insects may not work on mites. Some treatment options include: abamectin (Avid, Abamectin), acequinocyl (Shuttle), bifenthrin (Onyx, Talstar), etoxazole (TetraSan), fenazaquin (Magus), hexythiazox (Hexygon), spinosad (Entrust), insecticidal soap and summer oil. Repeat treatments may be required to get spider mite populations under control.

Author:
Sarah Hughson

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