10 things York Region residents need to know to protect trees from spongy moths

Yorkregion.com
May 20, 2022

They’re baaaack!

These icky insects may have a new name, “spongy moths,” but they’re up to all the old bad habits: destroying leaves, weakening trees and leaving their poop and skin rash trails everywhere.

But don’t despair. The end may be in sight, says York Region invasive species specialist Dayna Laxton.

Here are Laxton’s tree-saving tips:

1. They’re hatching right now.

Last week’s heat really kicked things off, Laxton says.

“You could see caterpillars starting to emerge from egg masses, just when leaves are filling out on trees.”

They’re tiny now and they’ll hang out where they are for a little while, she says, but soon, the feeding begins …

2. They’re more mobile than you think.

It’s called ballooning. Those hatching egg masses on your tree won’t necessarily stay there. Larvae dangle in the air and wait to be blown by the wind, which is also why controlling them is challenging.

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3. Tiny bites first.

Because they’re minuscule right now, you might only notice a few small holes and an odd eaten leaf.

But once those caterpillars grow, they’ll start chowing down in a big way.

That’s why we tend to see major defoliation at the end of June into early July.

4. Burlap’s best.

Burlap bands don’t trap and kill the pests; they are a collection tool.

Caterpillars feed on leaves at night when it’s cooler, and congregate in the burlap away from the day’s sun.

Pick them off midday or later, when it’s hot and you’ll find the most hiding in their shady refuge.

A two-day soak in soapy water will kill them, then dump them -- but wear gloves. Their tiny hairs can cause an itchy allergic reaction.

5. Now’s the time get wrapping.

We’ve missed the egg-scraping phase; they’ve already hatched. But burlap bands won’t work yet, because the big feed hasn’t started and they’re too small to pick off.

That day is coming, though, so get your trees wrapped now, to prepare. They get big, fast.

Check with your local municipality -- many are giving out burlap -- or go to your local hardware store. Instructions are available at York.ca/spongymoth.

6. Talk to a tree specialist.

Now is also time to talk to a licensed tree care company about trees you are concerned about, because they may have options for insecticides or pesticides.

They may also help if you’ve got trees that were badly damaged last year. Usually, they’ll bounce back, but they may benefit from fertilizer, etc. to help them along.

7. They’re here to stay.

Every seven to 10 years, the spongy moth population reaches a level where they become a real nuisance, like last year, then the population crashes.

No amount of spraying or treating trees is going to get rid of them. It’s part of our landscape now and we’ll forever have that cyclical cycle of growth years, and years where we don’t even notice them.

8. This year we might get lucky.

Regionwide monitoring of egg masses, conducted in the fall, found numbers significantly lower than previous years.

“I’m very hopeful that we’re actually at the beginning of what could be population crash in York Region,” Laxton said.

There are also signs the naturally occurring virus that helps reduce the population is spreading in areas with high concentrations.

Another promising sign: several sustained winter cold snaps may have killed off viable eggs that were exposed to wind or above ground.

9. There are still hot spots.

There will still be heavy to severe defoliation in some parts of the region this summer, Laxton said.

“It’s a very ‘hot spotty’ pest. Last year, Markham was hit pretty hard, but there are other small pockets in all municipalities.”

Laxton expects some neighbourhoods will be impacted again this year, but it’s too soon to say how badly.

Defoliation surveys in July will show damage more clearly.

10. Some trees are more vulnerable.

Trees are resilient and many come back after a bout with these pests, but some have a target on their barks.

Oak trees are like candy to spongy moths, but they will feed on a whole host of other hardwood species or deciduous trees.

Birch is another favourite, as are maple, willow and, under really severe conditions, coniferous trees like spruce and pine.

Urban trees are also more vulnerable because of the stressors they face, as are bigger, older trees that may not have the energy to endure the onslaught.