Boxwood spider mites control

Asked September 25, 2019, 9:28 PM EDT

I’ve discovered that the boxwood hedge around my garage probably has a spider mite infection. The leaves have lots of tiny yellow spots as well as larger yellow spots 2-3 mm across, and tiny black spots on the underside. The online advice is for spring and summer treatments. At this point in the year, what’s the recommended treatment. Is it too late for lady bugs. The whole hedge is infested. It’s on the north east side of the house, so, morning sun.

Oakland County Michigan boxwood

3 Responses

Hello,

Yes it is too late in the season for using lady beetles.

I agree the tiny yellow stippling looks like spider mite damage. For small populations repeatedly spraying a strong spray of water will knock mites off and they cannot crawl back up. More continue to hatch so, repeated water sprays are needed For larger numbers of spider mites, use a light(summer weight) horticultural oil or insecticidal soap. Note that these products are not from your kitchen, but are specifically formulated garden products found at garden retailers. There are miticides available, too. See the references below.

The light circular yellow spots may be a different issue. Boxwood blight has been found in Michigan and you need to be aware of it. (Reference below) if these round spots are not blistered, as when the shrub has leafminers, then it could be boxwood blight and needs to be checked by a lab.

You can submit branch samples to MSU Plant Diagnostic lab for an exact diagnosis. Double bag and seal samples tightly in case it is boxwood blight. Include pictures of the whole plant and a close up of the problem. The diagnosis will include actions you can take for the problem. See the web site for fee schedule and instructions-

https://pestid.msu.edu

Here are references-

https://hgic.clemson.edu/factsheet/boxwood-diseases-insect-pests/

https://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG52_IPM_Boxwood.pdf

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I picked up some Bioadvanced 3-in-1 Insect disease & Mite Control & applied it today. The whole hedge is discolored by the infestation & I hope it can survive the winter.
I took some pictures & cut some samples if you would like them sent.larger circles appear to be leaf miners (bubbling). Thisinfestation has manifest about 1.5 years since I added 3 new shrubs which I bought from Costco spring of last year Three additional shrubs were planted in pots & did not sieve the winter . They turned yellow and no new growth in the spring. I’ve had the rest of my hedge for >15 years

Hello,

The shrubs should survive over winter if they go into winter well hydrated. Be sure to keep them watered this fall until the ground freezes.

Evergreens never go completely dormant so, they need to be hydrated up to freezing when their roots can’t absorb anymore water.

Insects like mites and leafminers are always present in our environment. Some years they have higher populations than others. Also, shrubs under drought stress will be more susceptible to insects and diseases. Read the label on your product and treat the shrubs a second time next season.

Your shrubs in containers probably didn’t survive because the roots had no natural insulation around them, as they do when they are planted in the ground. If you try this again, you should either sink the pots up to their rims for the winter. Another technique is to gather the pots together, stack straw bales all the way around the containers, and top them with leaves or shredded bark. Remove the insulation in early spring and set the pots out. Water them as soon as the soil in the pots is thawed.

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