I have been clearing the little gauzy bundles of larvae from my boxwood bushes by hand. I haven’t found any caterpillars yet but I would do the same. Would it be helpful also to spray the boxwood bush with vinegar and/or mild dish soap diluted in water? Thank you!
Sorry to hear that your boxwoods have been attacked by the dreaded box tree moth.
As Master gardeners we do not recommend the use of home made remedies. In fact using a dilution of dish soap can actually harm your plants. The following is from one of our archived posts: ” There is a difference between soap and detergent. We use detergent to wash dishes and our clothes because it is a degreaser and an emulsifier. The problem with this on our hair, skin and leaves of plants is that it strips the natural protection from the surface…
I am providing a link to an article explaining the difference between detergent and soap as well as one on how to use soap as a pesticide safely. It is written from a scientific perspective and in lay language, explaining the thinking behind the comments above.”
Picking off the larva is a great way to reduce the population of caterpillars feeding on your shrubs. With regard to a treatment for Box Tree Moth Landscape Ontario recommends the following “Box tree moth larvae can be effectively managed with a safe biological insecticide (Dipel 2X DF PCP#26508), a product already registered for use in Canada. In fact, this is the same biological insecticide that is applied by air over the City of Toronto to combat Gypsy moth larvae in the spring. Dipel 2X DF contains a naturally occurring bacterium, Bacillus thuringiensis (B.t.), that when sprayed on the foliage, is consumed by the larvae as they feed on the leaves. Within an hour of ingesting the B.t. residue, the larvae stop feeding and then die within two-three days. Foliage needs to be retreated at least every 10 days to keep an effective layer of B.t. on the leaves during periods of larval activity. We found that one application per larval generation was usually enough to kill actively feeding larvae.” Bacillus thuringiniensis (B.t.) is available at your local garden center. Make sure to read directions on the label before applying.
For additional information on this pest:
Landscape Ontario box tree moth resource page: https://landscapeontario.com/tag/box%20tree%20moth
Ontario nursery crops blog (also for landscape plants) by Jen Llewellyn; search box tree moth: https://onnurserycrops.com/