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Twospotted spider mite

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Tetranychus urticae
Written by: 
Jon Clements


Frank Peairs, Colorado State University, Bugwood.org

Content adapted from MyIPM/Bugwood Apps

OVERVIEW

Twospotted spider mite is a secondary (non-fruit damage) pest of apple and pear. It is widespread in range, has multiple generations per season, easily develops resistance to miticides, and is particularly problematic when it is dry and moves from the ground cover into fruit trees.

BIOLOGY

Adults are pale yellow to dark green, brownish, or faintly orange. Males are smaller than females, have a distinctly pointed abdomen, and darkish areas on each side of the body. Females are more oval, and when newly hatched have namesake distinct dark areas on each side of the body, which becomes more blotchy and irregular when feeding commences. Nymphs also have distinct two spots. TSSM overwinters under bark or in the ground cover. In spring they typically move to weeds and grass where they feed. In summer they crawl into the canopy especially when it gets dry or the orchard floor is mowed. Once in the tree a serious infestation can develop and cause damage which is grayish bronzing of foliage in apple and solid dark-brown spotting of pear leaves.

MONITORING

Check foliage for mite presence beginning in early summer. 10 leaves from 10 trees should be averaged for a count, Chemical treatment is advised if there are six or more mites per leaf. Also check foliage touching ground cover on lower limbs. Summer oil sprays are advised, but a spring oil spray is not effective on TSSM because – unlike European red mite -- they are in the groundcover. If miticides are necessary, only use if over threshold and rotate chemistries for resistance management. If you can identify mite predators, then one predator per leaf on average may justify holding off on applying a miticide. (See http://www.ipm.msu.edu/insects/twospotted_spider_mite for help.)

Adapted from ‘Common Tree Fruit Pests,’ Angus Howitt, Michigan State University, 1993

MANAGEMENT

Chemical Control

Summer applications of miticides are indicated. Early season oil applications are not effective.

Specific Resistance Issues

Resistance is likely when miticides are not rotated. Be sure to rotate miticide classes when choosing chemical control.

Non-Chemical Control

Minimize weed growth, particularly broadleaf weeds, in the orchard. Mow frequently to keep groundcover short, but avoid mowing during hot/dry spells.

Adapted from Extension Bulletin E154 “2015 Michigan Fruit Management Guide for Commercial Fruit Growers” https://shop.msu.edu/product_p/bulletin-e0154.htm

 

EXTRAS

From UC Statwide IPM Project: Webspinning mites produce a characteristic blackening of pear leaves when they feed. Pear trees can tolerate fewer webspinning mites than European red mites. Usually two to three mites feeding near the midrib of a leaf produce black areas from the midrib to the margin. This blackening may appear even after mites have been controlled, especially if a period of hot weather follows the spray application. High mite populations may cause defoliation. Severe defoliation can stunt fruit and may cause the trees to bloom in fall, thus reducing next year's crop. However, if defoliation is limited to water sprouts in the top or interior of the tree, it will not adversely affect the crop or tree.