I have two 5 yr old, 6′ high boxwoods in 3’x3′ containers on the rooftop – full sun. I’ve just noticed patches of brown dead leaves throughout the bushes. There appears to be mini cobwebs and little specs but no movement. The bushes have always been strong and healthy. What is this pest and what may I do about it? Thank-you!!!
Although boxwoods are fairly resistant to pests, there are a few to which they are susceptible. As you are seeing no visible movement, tiny specs and some webbing, your boxwoods may have an infestation of Eutyletranclus buxi, or boxwood mite, a type of spider mite. The boxwood mite feeds on both leaf surfaces and all stages (larva, nymph) can cause damage. The eggs are laid on the under surfaces of the leaves where they overwinter. The larva and nymphs feed on the boxwood. Boxwood mites breed rapidly and there can be many generations over the course of a summer.
There are several ways you can try to control or eradicate boxwood mite:
- apply dormant oil to your boxwoods according to manufacturer’s instructions in the overwintering egg stage to prevent an infestation next year
- very regularly spray your boxwood with a strong spray of water to dislodge; this will also reduce the dry hot conditions that the mites prefer
- apply a horticultural oil (a 1 – 2% oil to water solution) during the summer. This will kill all stages of the insect.
Here is link to a fact sheet from Clemson University on Boxwood Diseases and Insect Pests which you may find helpful. https://hgic.clemson.edu/factsheet/boxwood-diseases-insect-pests/
While in Ontario, most applications of insecticides is prohibited for cosmetic and home there are approved dormant and horticultural oils and insecticidal soap containing only permitted ingredients which you can try. You will find these at your local nursery.
If you are diligent it should be possible to eradicate the mite.