Boxwood Leafminer Control for Homeowners and Landscapers
For minor infestations, some gardeners choose to prune off affected foliage in early spring before the adults emerge. This reduces the population of the pest but offers limited results in the case of heavy infestations as populations can explode from unpruned foliage.
Chemical Control Timing
Chemical controls are the best protection for complete control of Boxwood Leafminer. The most effective control of Boxwood Leafminer targets the larval stage because it is a long window and control is likely effective. Systemic insecticides applied just after the eggs hatch - for example, mid to late June in central Virginia - are the most effective. As boxwood flower in spring, waiting till eggs hatch avoids treating while pollinators may be visiting. Since the larvae are alive, eating, and growing during the summer and fall, research has found a systemic insecticide spray can be very effective when applied throughout the summer and into the fall. The efficacy of the spray drops when temperatures turn seasonally cold, which in some years is not until late October or early November. When these chemicals are applied properly and thoroughly to all boxwood in a given area, they eradicate nearly the entire population and it takes several years for a population to return to noticeable levels.
It is unnecessary to time a chemical application that targets Boxwood Leafminer adults. Because the adults only live a few days, an adult-targeted spray would have to take place every 2 or 3 days over a two week or more period. This control strategy is futile.
Home Landscapes and Gardens
Consult your state’s Cooperative Extension service for pesticide recommendations. Carefully follow the label information.