City of Hamilton, RBG aerial spray to reduce spongy moth caterpillars

The City of Hamilton and Royal Botanical Gardens (RBG) started an aerial spray to reduce the population of spongy moths, formerly called “gypsy moths” in areas that are out of control.

Spongy moths are an invasive species that feed on tree leaves and in some cases evergreen needles. The pesticide called BTK doesn’t fully remove the caterpillars, it just regulates the population.

“It infects the spongy moth larval form, and eventually it causes enough of infection that it kills them. So the reason we sprayed is that we’ve had two really, really bad years of complete defoliation,” said Charlie Briggs, a gardener at the RBG.

The City of Hamilton says staff members do ground sprays as well but aerial sprays are only allowed when the population is out of control which is why only some locations were sprayed today.

Briggs says the spray has minimal impact on the environment and other insects but it can still harm other caterpillars as well. Briggs says it has to be done, “you have to treat them or else they’ll consume all the food that’s leftover for the future generations of other butterfly and moth species.”

Trees that were impacted do recover and grow back more leaves in a few weeks if they’re healthy but if it happens multiple times it could be problematic. As a result, so far only a handful of trees had been taken down in the city.

Briggs says if you are dealing with spongy moths in your yard there are a few steps to prevent it. Throughout the winter if you notice egg masses, you can scrape them all off. If you notice caterpillars, you can skirt the tree with a piece of burlap or twine. “You’ll find the caterpillars hidden under it [burlap] during the heat of the day and you’re able to collect them and dispose of them in soapy water.” You can buy BTK at stores.

Today was the first aerial spray, the second application will be done in about seven days.