Winter Moth

Winter moth (Operophtera brumata) is a lepidopteran insect pest that was introduced into North

America from Europe. It has warranted control measures in Washington and Oregon and is now in Massachusetts in coastal areas from the North Shore, down around Boston, through Plymouth County, South Shore, and out onto Cape Cod as far as Chatham. It has also been identified in Rhode Island.

Susceptible deciduous plants include: oaks, maples, basswood, ash, crabapples, apple, blueberry, and certain spruces such as Sitka spruce. The insects seem to prefer fruit trees.

Plant Injury and Life Cycle

The young larvae (caterpillars) are tiny, pale green inchworms that tunnel into the buds where they feed. Larvae have a distinguishing white longitudinal stripe running down each side of the body. They move from bud to bud to feed. If bud opening is delayed due to cool weather conditions bud death can occur as the caterpillars have a longer time to feed. Older larvae feed in the expanding leaf clusters and are capable of creating defoliation in high populations.

Heavily defoliated trees will be severely stressed and must put out a second flush of growth in order to survive. Water is critical to trees at this time. Supplemental watering of trees will be necessary if a drought or if little rainfall occurs naturally. Fertilizer application is not recommended for trees that have been defoliated.

Adult moths emerge from the soil usually in late November and can be active into January. The adults are strongly attracted to lights and can often be found flying around  outside lamps or holiday lights. Males are small, light brown to tan, and winged; females are gray and wingless and since they can’t fly are usually found at the base of trees. After eggs are laid, the adult moths die and the eggs over-winter. Eggs hatch in spring when temperatures average around 55oF. Newly hatched larvae often crawl up tree trunks and produce a long strand of silk which makes them air buoyant. Larvae may also drop to plants that are growing beneath infested trees. They may then feed ona whole host of herbaceous perennials, roses, etc.

Controls

Various natural controls, such as flies and wasps, have been introduced to combat this pest in Washington and Oregon, with varying degrees of success.

A dormant oil spray to tree trunks and branches may kill the over-wintering eggs before they hatch. However, some egg clusters are protected by bark flaps and loose lichen. Eggs may also be in other locations onor off the host plant.

There are also products that act as a barrier to climbing caterpillars or for the climbing adult female moths in late fall to early winter. This is know as tree banding. The  products are generally heavy-weight paper strips that are covered with a sticky substance. However, research does not yet support their effectiveness and they are not recommended.

Bacillus thuringiensis (kurstaki), commonly known as B.t.k., is a bacterium specific to moth and butterfly caterpillars and it is effective on the younger larvae while they are free feeders (not in the buds). It must be ingested to be effective.

Spinosad is another biorational compound that is effective against winter moth. It is available under various brand names, such as “Bull’s Eye BioInsecticide” and “Monterey Garden Spray.” Spinosad can be highly toxic to bees at the actual time of application.

Insecticidal soap may be effective against younger caterpillars but only when they are exposed on the host plant.

Chemical insecticides, such as Sevin, are labeled for these pests. When using pesticides always read, understand, and follow all label directions. When considering the chemical insecticide option, the more conservative choices now are the pyrethroids.

Source: UMass Extension; prepared by Robert D. Childs, Deborah C Swanson, and Dr. Joseph Elkinton, last reviewed March 22, 2007

Useful Website

Massachusetts Department of Agricultural Resources Defoliator

http://www.mass.gov/agr/pesticides/pestfacts/Defoliator_caterpillar.htm