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Bald Cypress Rust Mite

August 5, 1998

This microscopic mite is an eriophyid mite that is most active during the warm season. The mite is active now in Ohio, and characteristic damage is being seen in Illinois. Damage will appear as reddish brown interior needles.

The bald cypress eriophyid overwinters as plump females tucked into the crevices of the bark. After the new leaves form, these females reproduce, and slender mites begin to infest the needles. The mites rasp through the needle surface and extract the cell contents below. As warm weather arrives, the mites "bloom"--thousands can be found on a single leaf. You can see these mites with a 10-power hand lens, but their numerous, white cast skins are the easiest diagnostic characteristic. The mites themselves are a light brown color.

As the mites continue feeding, the needles of the leaves become yellowish and then reddish brown. In the past, this level of damage was not noticeable until late August. The mites are still quite active and may cause some undue stress to bald cypresses. Thus, damaged trees are likely to require treatment.

Unfortunately, bald cypress is very sensitive to horticultural oils--unlike hemlocks, spruces, and junipers. If you try to control this mite with oils, you'll do more damage than the mites! Therefore, you should rely on a more traditional pesticide. Carbaryl (Sevin), dicofol (Kelthane), and oxythioquinox (Morestan) will knock down this mite, but thorough coverage of the foliage is necessary.

Author: Phil Nixon Dave Shetlar (The Ohio State University)


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