Officials with the Department of Environment, Energy and Forestry are advising property owners that Prince Edward Island may be about to experience outbreaks of forest tent caterpillars similar to the outbreaks which occurred in late June 2004. Over the past few days, forestry staff have been taking calls from Islanders who are concerned about the growing presence of these forest insects in certain communities.
“Right now we are getting reports from the Georgetown area about large numbers of immature caterpillars,” said David Carmichael, horticultural technician with the department. “However, I think we can expect to see more calls from northeastern PEI and areas west of Summerside in the coming weeks.”
The forest tent caterpillar is a native insect which eats the leaves of several deciduous tree species and can cause serious defoliation in some areas. While this can look quite bad, Mr. Carmichael said these effects are usually short term and most trees and shrubs will recover easily and establish new foliage.
Every 10 to 12 years, forest tent caterpillar populations explode, causing heavy, but usually localized, defoliation. The insect’s natural cycle means that populations build over several seasons setting the stage for recent outbreaks. Last winter’s conditions were favourable for egg survival and the long, cool Island spring provided plenty of food for the newly-emerged larvae.
When they strip off the edible foliage, the caterpillars migrate from tree to tree in search of more food. They prefer hardwoods such as poplar, sugar maple, white birch, and willow, but will eat other species when food supplies become short. When high populations result in complete defoliation, the caterpillars will move and this mass movement can be an incredible sight, leading many people to call them “armyworms.”
Mr. Carmichael said that most control methods are impractical once the outbreak occurs.
“The sheer numbers of insects means that killing hundreds or thousands will have little or no effect because there are so many more moving in to take their place,” he said.
For people who do want to try and deal with the outbreak, he offered the following advice:
-Water can be used to spray the caterpillars off small trees and shrubs.
-Special insecticidal soaps can be used to kill them but in order to be efficient, the soap must be sprayed on the caterpillars, not just on leaves.
-Sticky bands can be wrapped around the trunk to stop insects from traveling up and down the tree. These bands can be purchased from garden centres or made at home by using duct tape and a waterproof sticky material such as petroleum jelly.
Insecticides such as Malathion or Methoxychlor can be effective, but they are difficult to apply on large trees. Such chemicals also need to be used with caution so that they do not affect neighbouring properties. Mr. Carmichael noted that the label contains vital information on toxicities and any potential damage to other garden plants and beneficial insects. Bt., a bacterial insecticide, can be applied next spring when the leaves emerge to kill off the larvae which feed on the bacteria-coated leaves, but it will not do much to address this year’s problem.
“The good news is that these insects provide a vital food source for many foraging birds and that they should near the end of their feeding stage by early July,” said Mr. Carmichael. For more information on forest tent caterpillars, visit http://www.foresttentcaterpillar.ca/ or www.gov.pe.ca/go/forestpests.
For more information please contact:
David Carmichael, Horticultural Technician (902) 368-4711.