Spruce spider mites

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Spruce spider mites are often a problem on fir and spruce trees, but populations can build up on nearly all Christmas tree species. Spruce spider mites are considered a cool season mite and thrive when daytime temperatures are in the 60’s and 70’s. We have found mite activity on Fraser and balsam fir. Newly hatched larvae are pinkish in color, but turn dark green or dark red after initial feeding. Growers should keep an eye out for the dark mites or their webbing, especially if you had damage from mites last year. These mites are small, about the size of a period at the end of a sentence. Scout the oldest foliage, near the stem of the tree – that’s where the mite populations build up first. Rap foliage over white paper or cardboard on a clipboard. If mites are there, you should see them moving on the paper. If you see a few mites, but damage does not appear to be heavy, give it another seven to ten days and check the trees again. There are several naturally occurring predators that feed on spider mites and you want to give them a chance to do their thing. Predatory mites are the most important predators of spider mites, but are very difficult to see without a microscope. If you check the trees and mites seem to be abundant, especially if you plan to sell trees this year, then you may want to apply a miticide. If you are spraying Christmas trees for spider mites, do everything you can to get good coverage.

Here is an excellent reference from Pennsylvania on spruce spider mite by Rayanne Lehman http://ento.psu.edu/extension/christmas-trees/information/pest-fact-sheets/Spspidermiteent069.pdf/view

Spruce spider mites
Spruce spider mite.

Spruce spider mite
Spruce spider mite.

mite damage
Heavy mite damage on a Fraser-fir.

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