Hi and thanks for reading my question. I have one set of two boxwoods that are about 4 years old that I transplanted from containers to garden bed and another set of three that I planted last spring. I have been treating both sets of boxwoods for Psyllid this spring and I have just discovered those awful leaf miners now in adult form swarming around the older set. I understand the only way to really get rid of this pest is to either harshly trim the plants (I don’t have a huge garden, so this will be very noticeable and ugly) or hire a pro to use neonics (I don’t even know if the pros can use neonics – but I don’t want them used in either event). My #1 question is, would you immediately remove the most affected boxwoods before they infect the other set of three? I am so mad because I did trim them up this spring and they all look so darn healthy and attractive at the moment! My #2 question is – can leaf miner infest any other plants, or do boxwood leaf miners only infect boxwoods? In other words, should I be worried about other specimens in my garden, in which case I will definitely remove the affected plants as I have too much $$$ invested in the rest of the garden! Thank you very much!
Thanks for contacting the Toronto Master Gardeners about your boxwood problem. Without a photo I can’t confirm if the issue is indeed the boxwood leafminer, but the tell-tale signs are blisterlike, yellow/orange spots on the underside of the leaves. That’s where the larvae of the boxwood leafminer midge are living between the upper and lower coatings of the leaves.
If you decide to plant boxwood, Buxus, in the future choose varieties that have been cultivated for disease resistance. This includes cultivars of the English Boxwood, Buxus sempervirens and of the dwarf form- Buxus microphylla. Another alternative to planting resistant varieties would be planting anative alternative such as inkberry holly (Ilex glabra)(which would probably be the most similar) or Eastern white cedar (Thuja occidentalis) (which also has several smaller cultivars) which can be used for similar effect but additional ecological benefits and will have no risk of boxwood leafminer.
To address your question about the leafminer migrating to other plants, there should not be an issue as they only host on boxwoods, and here is more information on that topic: Boxwood Leafminer
You’ll find some steps to take in this answer to a previous question on the same topic:
In addition to suggestions about pruning in the link, if the infestation is small (or if you’re very patient) you can also squish individual leaves between thumb and finger to kill the larva inside.
Another link with information on this and other boxwood leaf problems is below. Keep in mind that any U.S. links might suggest pesticides (insecticides or herbicides) that are banned from cosmetic use in Ontario. I hope this helps. Good luck with your rescue operation.
May 31, 2022