Twospotted spider mite
Tetranychus urticae Koch
Adult and nymphal mites are yellowish to pale green with a dorsal pair of apparent dark "spots" (actually internal tissue contents visible through their cuticle) (A). Males are smaller than females and have a pointed abdomen. The female takes on an orange tinge in the fall (referred to as the "carmine phase") (B). They live in small colonies and aggregate in the crevices of the bark or in the ground cover to overwinter. Eggs, spherical and translucent, are laid individually on the underside of leaves (C).
Widespread and a major pest in most fruit-growing states and provinces in eastern North America.
Attacks all deciduous fruit trees. Leaves become speckled (D; damaged leaf on left, healthy leaf on right) as a result of mite feeding. In pears, leaves turn dark brown or black (E), especially if intense feeding occurs over a relatively short period. A serious infestation can delay tree growth, reduce fruit size and cause premature drop.
These mites move into the trees from nearby dying weeds; monitor foliage and watch for outbreaks following herbicide applications to broadleaf weeds in early to midsummer. Use miticides (based on thresholds) or horticultural mineral oil to reduce numbers during the summer period. A selective pesticide program may allow biological control by predator mites, glassy-winged mirid bug (Hyaliodes vitripennis) or Stethorus punctum.
The MSU IPM Program maintains this site as an access point to pest management information at MSU. The IPM Program is administered within the Department of Entomology, fueled by research from the AgBioResearch, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.