Boxwood Leaf miner infestation - what insecticide is permissible and when should it be applied? - Ask Extension
Several Master Gardeners diagnosed my 20 or so, 4 ft tall boxwoods with Boxwood Leaf miner. They are completely infested. I am a Master Naturalist a...
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Boxwood Leaf miner infestation - what insecticide is permissible and when should it be applied? #615448
Asked March 03, 2020, 9:02 AM EST
Several Master Gardeners diagnosed my 20 or so, 4 ft tall boxwoods with Boxwood Leaf miner. They are completely infested. I am a Master Naturalist and do NOT want to hurt any beneficial insects like bees, ladybugs or butterflies so how do I treat my Boxwoods? Is there a specific, effective treatment or insecticide I can use to eradicate these insects inside my boxwoods without hurting other insects? What do you recommend?
Montgomery County Maryland
Expert Response
There are a couple of approaches you can take with as little non-target impact as possible. Some boxwoods tend to flower in early spring (Asian species and hybrids) while others flower later in spring ("American" and European varieties), so it's likely that any sprays will miss the pollination season when bees are visiting the flowers. (You can always avoid using treatments when they are in bloom.)
A topical treatment for when the adults are out (typically late April to early May, depending on temperatures) would be trying a product with the active ingredient of spinosad. A systemic treatment for larvae - and as such offering longer-lasting control - would be a product with the active ingredient of acetamiprid. This has been shown to have very low nontarget effects (not harmful to beneficial insects) and would be the preferred systemic for this reason. It is only available to certified commercial applicators, however, and thus a landscaping company would need to apply it for you. Given the size and quantity of plants involved, this might be a reasonable approach either way.
Miri
A topical treatment for when the adults are out (typically late April to early May, depending on temperatures) would be trying a product with the active ingredient of spinosad. A systemic treatment for larvae - and as such offering longer-lasting control - would be a product with the active ingredient of acetamiprid. This has been shown to have very low nontarget effects (not harmful to beneficial insects) and would be the preferred systemic for this reason. It is only available to certified commercial applicators, however, and thus a landscaping company would need to apply it for you. Given the size and quantity of plants involved, this might be a reasonable approach either way.
Miri
