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Rhonda Ferree's ILRiverHort

Rhonda Ferree's Horticulture Blog

Watch for Mites on Evergreen Trees


University of Illinois Extension Horticulture Educator Rhonda Ferree warns homeowners to watch for mite damage on evergreen trees and shrubs.

Hot, dry summers result in increased mite feeding on plants. Ferree most commonly sees mite problems on the dwarf Alberta spruce, but they can attack a wide range of plants. Spruce spider mites are one of the most damaging pests of spruces and many other conifers. These mites suck sap from the undersides of the needles and cause the green pigment to disappear. Large areas of affected trees show reddish brown needles that drop easily. Young spruce trees may die the first season. If left uncontrolled for several years, older trees may die, with symptoms progressing from the lower branches upward.

To determine if your tree is infested with mites, hold a sheet of white paper underneath some damaged needles and tap the foliage sharply. Tiny dark green to black specks about the size of pepper grains will drop to the paper and begin to crawl around. The pests are easily seen against the white background. Upon closer investigation under the microscope I have seen silken webbing on the twigs and needles and usually can find small clear eggs.

To control the mites non-chemically, use forceful water sprays to knock mites off the plants. Chemical sprays can be applied now when the mites are numerous. Concentrate spray on underside of foliage and repeat in 5 to 7 days. For a listing of approved products, contact your local Extension office by visiting www.extension.illinois.edu. Since mites are not insects, insecticides will not control this pest. Several natural products are labeled for spider mite control, including canola oil, clove oil, cottonseed oil, and insecticidal soap. Always follow chemical labels carefully.

With all pest problems it is important to maintain healthy plants that are better able to fight off pest infestations. Use proper cultural practices, including irrigation, fertility, and mulching, which will avoid stressing your plants. This will help minimize having to deal with high populations of insects and disease.



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