Help control spongy moth on your trees

Scrape egg masses from tree trunks by the end of April

Guelph, Ont., March 21, 2022 – Spring has arrived in Guelph which means it’s time to check your trees for signs of the recently-renamed spongy moth (lymantria dispar dispar), an invasive species in North America whose caterpillars results in loss of leaves to trees in the urban forest.

We recently did a second egg mass survey in November 2021, following a similar survey one year ago to determine the risk of defoliation to trees across the city. The recent survey found that the risk to Guelph’s urban forest this year is mild in comparison to surrounding communities.

What this means for City-owned trees

We’re going to continue to monitor trees on our streets and in our parks and natural areas for egg masses and spongy moth populations. You may hear other communities are managing spongy moth with aerial spraying of pesticides. With our risks much lower this year, we won’t be scraping egg masses or using pesticides to control caterpillars on our street, park or natural area trees.

Manage spongy moth on your private trees

You can help reduce the loss of tree leaves by scraping moth egg masses from the trunks and branches of trees on your property before they hatch at the end of April. Use online resources to help identify egg masses and a garden trowel to scrape eggs into soapy water. Leave them for a minimum of three days before disposing to make sure larvae are dead.

After the eggs hatch

Spongy moth caterpillars can be identified by the red and blue dots on its back. If eggs have managed to hatch on your trees, you can manage caterpillars by:

  • Installing sticky bands or burlap around tree trunks and emptying each day
  • Picking caterpillars off by hand
  • Spraying BTK products (a naturally-occurring bacteria) found in hardware stores
  • Installing moth traps
  • Hiring a licensed professional to treat trees with pesticide

Report spongy moth on City-owned trees online.

For more information

Timea Filer, R.P.F., Urban Forestry Field Technologist
Forestry and Sustainable Landscapes, Parks
City of Guelph
519-822-1260 extension 3352
[email protected]