Boxwood Leafminer

Host: Common Boxwood (Buxus sempervirens)

Symptoms

• Conspicuous egg punctures in leaves. Mines are not evident for several weeks.
• Oval, water-soaked swellings on the lower leaf surface evident from midsummer until shed.
• Infested leaves are spotted yellow and may drop prematurely.
• Continuous infestations result in dead twigs and a weakened plant subject to disease and winterkill.

Description

• Injurious stage: Larva. A yellowish-white maggot, 1/8".
• Monitored/Treatment stage: Adult. A tiny, yellowish-orange midge (fly), 1/10". (Systemics targeted at young larvae)

Life cycle

• One generation annually.
• Overwinters as a partly grown larva in the leaves.
• Grows rapidly in spring, transforming into an orange-colored pupa.
• Emerges as a fly in late May to early June over a period of 10-14 days (300-650 GDD).
• Eggs are laid deep in the upper side of the current season's leaves.
• Female lays an average of 29 eggs and dies hours after last eggs are laid.
• Eggs begin to hatch about 3 weeks after being laid.

Montioring Stage/Timing/Technique:

• Larvae: Inspect for presence November through March.
• Adult: Set out yellow sticky traps or look for swarms early in the morning. 300-650 GDD, end of May through June
• Weigela (Weigela florida) and yellowwood (Cladrastis kentukea [formerly C. lutea]) beginning through end bloom.
• Egg: Check newest leaves for pinholes in late June.

Management

• There are few known natural enemies of the boxwood leafminer.
• Severely shearing the foliage before adult emergence or after egg laying ends will reduce the overall population.
• Plant resistant varieties.

Written by: Robert Childs
Revised: 10/2011