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A Plague of Caterpillars

Written for Color Penfield Green's newsletter

Penfield residents who are already feeling overwhelmed by Covid restrictions might now be encountering another plague, gypsy moth caterpillars devouring trees and raining their frass (the scientific name for caterpillar poop) on driveways, decks and unprotected drinks. Some deciduous trees are already stripped and the caterpillars have moved on to nearby spruces. It’s too late for biological sprays to help and potentially harmful chemical sprays will be only partially effective. The good news is that deciduous trees are likely to survive a year or two of leaf stripping. Evergreens, however, do not readily regrow needles, so may not survive a serious infestation. What can a homeowner do to protect trees and limit the nuisance without bringing more harm to the environment?

Actions to Take This Year

  • First of all, if your trees are affected, give them some extra water; the dry conditions add extra stress.

  • Since the caterpillars feed mostly at night and look for shade during the day, you can reduce their population by wrapping the trunk of an affected tree with a burlap skirt and remove and kill any that take shelter during the day.

  • The tan male moths are already flitting around looking for the flightless white females. You’ll never catch up with the males, but females can be destroyed as well as any of the dark brown, tear-dropped shaped pupas that can be found attached to trees or nearby structure.

  • If you see buff-colored, fuzzy egg cases on your trees or any other surfaces, do not knock them off or spray them apart with a hose. The hardy eggs can survive on the ground. Do, however, either carefully scrape them off the tree and soak in soapy water for 48 hours or burn them. Alternatively, soak the cases with a specially formulated horticultural oil. Since the eggs won’t hatch until next spring, you can do this anytime through next April.

Actions to Take Next Year

  • If you have a bad infestation, you may want to consider having your trees sprayed with Btk, a biological control that won’t harm other insects. This will only be effective when the caterpillars are small.

  • Trees with thick bark can be wrapped with duct tape smeared with tanglefoot, a sticky substance that traps caterpillars as they cross. If trees have thin, delicate bark, wrap with paper then duct tape so the tape doesn’t adhere directly to the bark. Periodically comb off dead critters to make room for more. This is most effective in early stages, later you may want to switch to the burlap wrapping mentioned above.

Trees provide so many benefits to communities, among them: sequestering carbon, producing oxygen, filtering pollutants, cooling the air and protecting humans from too much sun. They are also home to many small animals and a huge diversity of insects that provide food for birds and animals, pollinate flowers and prey on harmful insects. Spraying trees with insecticides not only puts people’s health at risk, it kills insects indiscriminately destroying the caterpillars’ predators, pollinators, and the food supply of other creatures.

See the following websites for more detailed information on the above suggestions:

https://fyi.extension.wisc.edu/gypsymothinwisconsin/pest-management-2/management-guide-for-homeowners/

https://www.pubs.ext.vt.edu/2811/2811-1021/2811-1021.html



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