Douglas Firs may have spider mites - Ask Extension
We have six 60+ year old Douglas firs and a Cedar (closely related to Western Red but likely a cultivar) that appear to have an infestation of spider ...
Knowledgebase
Douglas Firs may have spider mites #877865
Asked July 18, 2024, 9:30 PM EDT
We have six 60+ year old Douglas firs and a Cedar (closely related to Western Red but likely a cultivar) that appear to have an infestation of spider mites. Can anyone confirm this? I can get more photos or submit a sample. I also need to know what to do, if anything can be done. The infestation appears to be pretty large but most of the limbs are too tall for me to reach or even see well. I hope the only answer is NOT to spray them with insecticide because that would have a huge impact on my native backyard habitat. I don't think I could do it. Thanks so much!
Multnomah County Oregon
Expert Response
I shall refer you to factsheets below on spider mites. These may help you confirm the identity and they also have recommendations for treatments both non-chemical and chemical.
In general, we don't expect spider mites to cause serious health problems for large Douglas-fir trees. Spider mite populations are usually controlled by natural predators by mid-summer. However, severe cases may warrant extra effort to mitigate impacts.
If you want further assistance to identify the pests, you would need to collect specimens of adults and send to the OSU Plant clinic.
To monitor and collect pest specimens: Observe the leaves for mites and/or mite eggs, stippling, or webbing. Using a stick, hit a branch over white paper to see if mites (moving dust specks) or natural enemies are present. For help with ID, collect specimens and send or drop off with OSU Plant Clinic's insect ID clinic https://bpp.oregonstate.edu/insect-id-clinic
See the factsheets below for more information.
https://hortsense.cahnrs.wsu.edu/fact-sheet/douglas-fir-spruce-spider-mite/
https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/douglas-fir-pseudotsuga-spruce-spider-mite
https://pnwhandbooks.org/insect/hort/landscape/common/landscape-spider-mite
In general, we don't expect spider mites to cause serious health problems for large Douglas-fir trees. Spider mite populations are usually controlled by natural predators by mid-summer. However, severe cases may warrant extra effort to mitigate impacts.
If you want further assistance to identify the pests, you would need to collect specimens of adults and send to the OSU Plant clinic.
To monitor and collect pest specimens: Observe the leaves for mites and/or mite eggs, stippling, or webbing. Using a stick, hit a branch over white paper to see if mites (moving dust specks) or natural enemies are present. For help with ID, collect specimens and send or drop off with OSU Plant Clinic's insect ID clinic https://bpp.oregonstate.edu/insect-id-clinic
See the factsheets below for more information.
https://hortsense.cahnrs.wsu.edu/fact-sheet/douglas-fir-spruce-spider-mite/
https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/douglas-fir-pseudotsuga-spruce-spider-mite
https://pnwhandbooks.org/insect/hort/landscape/common/landscape-spider-mite
