The winter moth was introduced to North America from Europe and was first recorded in Nova Scotia in the early 1930s. It has since spread all over coastal areas in the western and eastern United States.
For many years in Massachusetts, defoliation on the south shore near Boston was attributed to cankerworms, a native insect that was known to periodically defoliate in the area. Cankerworm outbreaks would typically last two or three years before natural factors caused their collapse. When collapse did not occur, it was suspected that another species was the culprit, which was soon confirmed to be winter moths. Winter moths feed on a number of deciduous trees and shrubs found in MA, including blueberry and rose bushes, cherry, apple, crabapple, elm, ash, maple and oak trees.
IDENTIFICATION AND LIFE CYCLE
Winter moth larvae hatch and feed on leaves and fruit beginning in early spring. Larvae feed on the insides of buds and leaf clusters during the day, inching their way to the outside of leaves at night. In June, larvae drop to the ground under trees where they bury themselves in the soil. Moths typically emerge from the soil in late November. The male moths, light brown to tan, are strongly attracted to lights and can often be found flying around outdoor lamps or holiday lights. The female is grey and almost wingless.
DESCRIPTION OF DAMAGE
Caterpillars feed on both flower and foliar buds. Once a bud has been devoured from within, the caterpillar will migrate to other buds and repeat the process. Destruction of flower buds can lead to a greatly diminished harvest for fruit crops. After leaf buds open, the small caterpillars can be found within the tight clusters of new leaves in the daytime.
Winter moth control should be approached in three steps:
1) Wrap your trees with a pest barrier such as Tanglefoot in mid-November to prevent the flightless female moths from climbing up the tree and laying eggs.
2) Spray the plant with horticultural oil such as Bonide All-Seasons Spray Oil or Ortho Volck Oil Spray in late March or early April before the buds swell and the leaves emerge. This will kill any eggs that may have been laid on the branches of the plant by moths last fall by suffocating them.
3) If the eggs have already hatched, apply product containing Spinosad.