DEM says winter moth caterpillars are defoliating trees throughout Rhode Island

Water is Critical to Counteract Stressed Trees

PROVIDENCE [DEM news release] - The Department of Environmental Management reports that winter moth caterpillars are prevalent throughout Rhode Island and are causing defoliation on oak, maple, ash, basswood, elm, beech and fruit trees.

According to Bruce Payton, deputy chief of DEM's Division of Forest Environment, some Rhode Island communities including Warwick, Cranston, Exeter, Richmond and Lincoln reported the emergence of millions of winter moths, Operophtera brumata, from late November through December.

"It is no coincidence that, in the spring, these same communities have witnessed an astonishing number of caterpillars defoliating deciduous trees," he said. The tremendous growth of the caterpillar population has spread from bay communities in Providence and Bristol counties to the entire state. Leaves on affected trees are filled with small holes and have a shotgun-hole appearance.

Winter moth caterpillars are pale green with white longitudinal stripes running down both sides of the body. Also referred to as "loopers" or "inchworms," they are often found in association with both fall and spring cankerworms, which look similar and have similar feeding patterns.

Payton said that heavily defoliated trees will be stressed, and that the trees 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 drought conditions occur. Fertilizer application is not recommended at this time for trees that have been defoliated.

In an effort to control the winter moth population, researchers from DEM in conjunction with URI and Joseph Elkinton, PhD of the University of Massachusetts Amherst released a parasitoid fly that feeds exclusively on winter moth in early May in several Rhode Island communities.

This is the second year that this parasite has been released in the state; the hope is that it will become established and eventually act as a control agent for the winter moth population. A natural enemy of the winter moth, Cyzenis albicans has been effective in mitigating large populations of winter moths in Nova Scotia. However it will take several years for populations of the parasite to catch up with the population and spread of winter moths.