Leafminers (Monarthropalpus flavus)

Leafminers are the most problematic insect pest for boxwoods in the New York area. These gall midges overwinter in the leaf tissue and become apparent in the spring when adult flies emerge from the leaf underside, leaving the evidence of holes and/ or tiny casings behind. Females then deposit eggs in the newest  leaves, typically in protected positions low and inside the plant. Yellow - orange swelling, sometimes blisters, appear on the leaves in late summer as the insects grow. If you remove the lower layer of a leaf, larval leafminers are exposed.

If you have problematic leafminer damage to your boxwood, control techniques should be applied at the time the adult insects are exposed and most vulnerable.  Ruffle the leaves of the shrub and look for orange, winged, adult midges, beginning in late April, when they emerge from the undersides of leaves and, for a period of three weeks, preparing to deposit their eggs. There is one life-cycle per year.

You can learn more about boxwood in our Guide to Boxwood. 

Courtesy of NYBG Plant Information Service