Boxwoods – Controlling Leaf Miners

Q: We have an extensive planting of boxwoods along the entire front and east side of our house. They are quite large, 45 to 50 years old. We are seeing branches and spots of leaves dying over almost the entire range of the shrubs. In February they were fertilized and lightly pruned. We have watered them during this drought. In past years we used cottonseed meal to fertilize when we could find it. A garden fellow from Milledgeville who has come by from time to time says we have leaf miners. What can you suggest to us? We feel like we are watching them die!

A: The leaf miner is a good guess. Typically, August is the month when homeowners notice the splotchy brown and yellow leaves caused by the miners. A fly-like adult laid eggs on the boxwood leaves in late spring. When the eggs hatched, the larvae chewed into the center of the leaf and happily munched away, protected from predators and the elements.

Leaf miners are very difficult to control once they are inside the leaves. The best way to control their numbers is to spray when the adults are present in April and May. Insecticidal soap or horticultural oil will kill them if the boxwoods are thoroughly sprayed. Synthetic insecticides like acephate (Orthene) or disulfoton (Bonide Systemic Rose and Flower Care) are absorbed by plant tissue, making it deadly to chewing insects.