Spider mite treatment for hemlocks?
Hi, I live in Troy and have 4 hemlocks (about 7' tall). Would it be appropriate to pay for early-season spider mite treatment for them? I will be getting "R6-Fall Foliar" treatment, and early and late season nutrient treatments. Thanks for your help! Elizabeth
Oakland County Michigan
I am glad you are being proactive about the health of your trees.
However, we don’t recommended regularly spraying preventive insecticides because they kill and reduce populations of predatory insects that naturally help control the damaging insects. It is best to monitor plants for spider mites and take action when they are present. The F6 product you referenced is a form of horticultural oil. These oils work on insects and eggs that are present, not on insects that appear later on. In spring through fall, a strong stream of water from a hose, or a heavy rain, can wash mites off and be helpful.
Also, monitor for Hemlock Wooley Adelgid, an insect that can kill hemlocks. Here are details- https://www.canr.msu.edu/resources/options_for_protecting_hemlock_trees_from_hemlock_woolly_adelgid_e3349
Similarly, we do not recommend fertilizing trees and shrubs unless there are signs of trouble- poor leaf color, less than average growth, leaf spotting, or smaller than average leaf size are all signs of potential nutrient deficiencies. A soil test is the best way to determine if nutrients are needed. If you haven’t had a soil test in the last 3 years, we recommend having one done, and use the results to guide your fertilizer program- https://homesoiltest.msu.edu
The best thing to do for trees and shrubs is to position them in the correct location, plant in the correct soil type, and to deeply water them during droughty times.
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Thank you, Laura! Your response was very helpful. I will take your advice and start with a soil sample in spring.
All the best,
You can send a soil sample as soon as the ground is thawed enough to dig at the correct depth. They are busy in spring so don’t delay. If you need help with the results, let us know!