NC State Extension Publications

Description and Biology

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Pine witches' broom mites, Trisetacus floridanus and other closely related eriophyid mites, cause noticeable bunched growth on pines often referred to as witches or witch's brooms. Eriophyid mites are unusual in that they have only four legs situated at the front of a worm-like, cylindrical body. Pine witches' broom mites are extremely small (280 to 375 microns long—just visible with a 10X hand lens), and the abdomen has 65 to 70 encircling rings with microscopic bumps. The tiny legs each have a feather claw with eight rays on each side. The light yellowish white female mites lay relatively large eggs from which hatch first nymphs that grow and molt into second nymphs that grow and molt into adult mites. Like many eriophyid mites, Trisetacus mites inject their saliva into their hosts as they feed. This saliva acts like a plant growth regulator by shortening stem growth and encouraging numerous adventitious buds to form (the witches' broom). Specimens have been collected in growing terminal shoots from January through August. Pine witches' broom mites probably overwinter in bark crevices and under bud scales. We probably have several generations per year in North Carolina.

An illustration of the pine witches' gall mite

An illustration of the pine witches' gall mite taken from Keifer et al. 1982. The entire abdomen has rings with micro bumps.

A damaged pine bud opened to show the eriophyid mites

A damaged pine bud opened to show the eriophyid mites inside (arrows). These mites are incredibly small.

Host Plants

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Pine witches' broom mites have been reported attacking terminal shoots and causing galls, aborted buds, and stunted needles on "pine," sand pine, slash pine, and cedar pines.

Photo of small witches' brooms on pine

Here are a couple of small witches' brooms on pine probably caused by Trisetacus floridanus.

Residential Recommendations

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Should pine witches' broom mites become so abundant on a specimen tree in the landscape that control seem necessary, Sevin insecticide is effective for eriophyid mite suppression. Use a sprayable formulation for better results.

Other Resources

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For assistance with a specific problem, contact your local Cooperative Extension center.

This factsheet has not been peer reviewed.

Author

Professor Emeritus
Entomology & Plant Pathology

Publication date: July 22, 2020

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