Programs for cities and counties

City managers should keep these two goals in mind when treating for gypsy moth (Lymantria dispar): (1) reduce the population of caterpillars enough to prevent defoliation and stress of trees and (2) relieve the nuisance. Remember, you don’t have to kill every Lymantria dispar caterpillar in town!

  1. Identify nearby areas with trees preferred by Lymantria dispar. These areas will be where you will first see defoliation and where it will be most severe. Trees favored by Lymantria dispar include oaks, crabapple, linden, willow, birch, and aspen.
  2. Select spots to survey within the areas you defined above. Homeowner complaints can also be used as starting points for your survey.
  3. Decide if the area is worth protecting. Residential areas and city parks would qualify as high priority, an industrial zone would not.
  4. Wait until the leaves have fallen before taking surveys to predict the amount of damage that Lymantria dispar could do the following summer.

Consider Lymantria dispar when planning tree planting

  • Consider planting trees that Lymantria dispar doesn’t like to reduce the amount of defoliation in town. View a list of favored and avoided trees.
  • Lymantria dispar will repeatedly defoliate oaks, crabapples, birch, willow, mountain-ash, and lindens. Avoid planting these species in solid groups.
  • Maintain the health of trees. A vigorous tree can survive defoliation where a weak tree may die or succumb to secondary pests like boring beetles or root rot. Watering, mulching, and avoiding root compaction or damage can be very important!

Mechanical control

Encourage homeowners to police their own trees. Mechanical control can reduce the number of Lymantria dispar caterpillars on trees whose canopies are separate, as in many residential settings. Removing egg masses and destroying them, sticky bands and burlap bands are all helpful in reducing moderate to high populations of the pest on specific trees. This activity also has the important benefit of helping people feel more in control of the situation reducing the anxiety that can cause people to use dangerous means to reduce the number of caterpillars.