Pest description and crop damage Apple ermine moth is an invasive insect from Eurasia that has established in the PNW. The adult insect is a long, narrow moth up to 0.4 inch long, white with small black spots, and long, backward-sweeping antennae. The larvae are greenish-yellow caterpillars, 0.5 inch long, with two rows of black spots down their body. The pupae are found in spindle-shaped white cocoons. The larvae consume foliage within communal webs or tents. These tents are much smaller in size than those of the tent caterpillars or fall webworm. This pest primarily affects unmanaged trees. The larvae could cause damage in commercial orchards with minimal insecticide inputs.
Biology and life history The insect overwinters as an immature larva under egg masses on the bark. Females lay 10 to 80 eggs in each cluster in overlapping rows like shingles. The egg mass forms a flattened, slightly convex oval about 0.5 inch in diameter. They are initially yellow, but age to red then gray in color. Larvae emerge at bud break and commence mining the leaves. Later, larvae tie together leaves with webbing to make nests up to 3 inches across. Each nest contains several caterpillars. New nests are made as leaves in old ones are consumed. The caterpillars pupate in clusters within webbing, beginning around June. Adults emerge from late June onwards, with females laying eggs into the fall. There is only one generation per year.
Pick off or prune out any egg masses observed on the bark in the fall. Prune out and destroy nests (in May) when practical. Also remove any pupating clusters when noticed.
Management-chemical control: HOME USE
- zeta-cypermethrin-Highly toxic to bees.
Management-chemical control: COMMERCIAL USE
Products used for leafroller and codling moth management will likely provide good control (including softer options). The following are labeled:
- beta-cyfluthrin (Baythroid XL) at 2.4 to 2.8 fl oz/A in no less than 100 gal water per application. Do not apply more than 2.8 fl oz/A per season. REI 12 hr. PHI 7 days. [Group 3]
- cyfluthrin (Tombstone) at 2.4 to 2.8 fl oz/A in no less than 100 gal water per application. Do not exceed 2.8 fl oz/A per season. REI 12 hr. PHI 7 days. [Group 3A]
- esfenvalerate (Asana XL) at 4.8 to 14.5 oz/A in up to 100 gal water per application. REI 12 hr. PHI 21 days.