Spray Schedule for Mites on Alberta Spruce Trees

Mites are arachnids, or members of the spider family.

Mites are arachnids, or members of the spider family.

Mites are tiny insects barely discernible to the naked eye. However, these tiny bugs can kill an Alberta Spruce (Picea glauca conica), a small conical evergreen thriving in U.S. Department of Agriculture plant hardiness zones 2 through 8. Symptoms of mites include stippling on the needles, followed by a yellow mottled appearance, finally resulting in brown, dead needles. Webbing may be present. Trees may eventually be killed. Regular spray programs can kill mites and keep populations in check. Sprays come in different formulations under varying brand names, so read labels carefully.

Winter Applications

Winter, for horticultural purposes, doesn't necessarily begin when the calendar indicates it does. While dormancy can be difficult to determine, when the weather begins to cool and leaves are falling off deciduous trees, Albertas are probably going dormant as well. You can control mites with horticultural oil from the onset of dormancy until the buds for new growth begin to swell and expand. Test a small area of the tree before spraying the entire tree to test for sensitivity.

Spring Applications

In spring, the eggs that were laid in fall or winter begin to hatch at the onset of warmer weather. These hatchlings will mature and lay eggs four to six weeks later, and the population will increase. At this point horticultural oils may help but will probably damage the newly emerging needles. By this time, insecticides containing acephate are useful and work through the system of the tree so anything eating it may be killed. However, it may also kill beneficial insects and birds, and can be dangerous to humans if applied incorrectly.

Summer Applications

Light infestations can be controlled with a frequent strong spray of water. This will knock mites off the Alberta spruce, but probably not kill them. Once new growth has hardened, you can once again spray horticultural oil. In addition, insecticidal soaps or malathion can be used. Insecticidal soaps must completely cover the mites so they can kill them by dissolving their protective membranes. Soaps have no residual effect but may harm foliage, so test a small section first. Malathion lasts 5 to 10 days and prevents the mite's nervous system from working properly. During hot weather, the mite's reproduction cycle shortens and multiple applications may be necessary.

Fall Applications

Damage is likely very visible by now if no prior attempts to control mites has taken place. Mite populations can be at their greatest during fall. Many sprays that can be applied during summer may also be applied during fall, such as summer oils, insecticidal soaps or malathion. In addition, you can apply neem oils, pyrethroids or pyrethrins. Neem oil disrupts the mite's hormones, but often doesn't kill them immediately. Pyrethrins are made from chrysanthemums, and pyrethroids are a synthetic version of pyrethrins. They affect the mite's nervous system.

About the Author

Lori Norris has been writing professionally since 1998, specializing in horticulture. She has written articles for the Oregon Landscape Contractors Association, chapters of the certification manual for the Oregon Association of Nurseries and translated master gardener materials into Spanish. Norris holds a Bachelor of Arts from Linfield College.

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