Landscape and Nursery - Boxwood Leafminer

Watch for boxwood leafminer activity this time of year. The following is a short article on the subject from Rutgers University.

BOXWOOD LEAFMINER: This particular host specific pest is a good example of why it can still be important to monitor plants during the off-season. Although the single generation leafminer larvae have been in boxwoods leaves since May, their presence in new foliage is often not readily apparent until the fall. Most of the activity and feeding damage by the fly larvae are done during the fall and winter. Blister-like blotch mines are now just becoming noticeable on current season infested leaves. While most insect pests are winding down for the year, the boxwood leafminer is just heating up. When symptoms suggest their presence, “break the back” of the leaf and peal away the lower epidermis to detect the still clear and thin larvae (usually several are found in each leaf). As feeding continues through the fall months, the larvae develop into larger, yellow colored maggots. After a mid-winter resting stage the larvae begin feeding again in late winter. With heavy infestations, defoliation can occur in the spring. The various neonicotinoid class root systemics should provide outstanding, long lasting results against this pest. As long as good root uptake of the material is achieved, success is usually assured. Within a week, sufficiently lethal insecticide levels should be translocated up into the boxwood foliage if healthy roots and adequate soil moisture are present.

Blotch on boxwood leaf opened up to reveal the boxwood leafminer larvae. Photo from Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Reprinted from "Landscape IPM Pest Notes" by Steven K. Rettke, Ornamental IPM Program Associate in the October 7, 2007 Edition of the Plant and Pest Adivsory, Landscape, Nursery and Turf Edition from Rutgers University.