A large number of boxwoods on our property have discolored leaves and are beginning to have leaf loss. It looks like there are little white bugs are...
Knowledgebase
Boxwood Bugs #668284
Asked July 24, 2020, 3:44 PM EDT
A large number of boxwoods on our property have discolored leaves and are beginning to have leaf loss. It looks like there are little white bugs are popping out of the underside of the infected leaves. (See attached photos of top and underside of leaves.)
A local nursery diagnosed leaf miners on samples taken in on three separate occasions. They recommended Bonide Systemic Insect Control, to be sprayed on 2-3 times, 10-14 days apart. I have made 2 applications.
Then the technician who sprays shrubs on our premises said the problem couldn't be leaf miners because they are active only through mid-May and it's now almost the end of July. The technician said the problem is mites. He sprayed the boxwoods with a different product that he said would last 30 days, and then the bugs would be gone.
What do you think?
Oakland CountyMichigan
Expert Response
Greetings! This is definitely boxwood leaf miner not mites. Looks like you did kill the emerging wasp (which is what is inside of the leaf once they pupate) because the little white things you see are the carcasses. Good job on the sprays. If there were any additional eggs laid, these larva are now inside of the leaf and sprays, unless a systemic, will not work. With heavy infestations, we often see a need for two seasons of control, although this pest can be somewhat cyclical. If you "peel" open some new foliage, you can check to see if there will be more next year.
Imidacloprid, a systemic insecticide (Merit or Bayer Tree and Shrub
Insect Control), will control the larvae inside the leaves and does not
require precise timing. This product should be applied in mid- to late
April. Imidacloprid has very low vertebrate toxicity; however, like
other neonicotinoid insecticides, imidacloprid is implicated as a
possible cause of honey bee decline.
Confirm the presence of larvae before applying a pesticide, either by
dissecting a leaf or holding it up to the light. Otherwise, symptoms
could be confused with disease or abiotic causes. Be sure to read and
follow all instructions and safety precautions found on the label before
using any pesticide.
Thank you for clearing up our confusion! I am the property manager and a resident of a condo association, and we have a lot invested in our boxwoods. I will wait til next April and spray the product you have recommended. The neighbors will all be pleased that a cure is possible.
You are welcome. This has been quite a year for boxwood leaf miner. I have two properties that have the problem as well. Keep in mind that this may be a multi year effort to control them. I think you are on the right track.
