bird with a caterpillar in its beak

Gypsy moth devastation

Depending on where you are in Muskoka, you may be horrified at the way your trees are starting to look, as gypsy moth caterpillars continue their work.

Then again, you may be fortunate enough that you are seeing little if any sign of gypsy moths — also known as LDD moths. This is a bad year for gypsy moths, but their presence is patchy and some areas have been hit much harder than others.

Gypsy moths are an invasive species — they were brought to North America in the 1860s and accidentally released near Boston. They’ve been spreading ever since, arriving in Ontario in 1969 and gradually moving northward.

Like many creatures, their populations rise and fall on a natural cycle and tend to peak every ten years or so. This current infestation began last year and was actually past due — the last major infestation was in 2002. The infestations usually last for two or three years before disease spreads through the moth population, knocking them back to much smaller numbers.

This is a particularly bad infestation — last year, nearly 600,000 hectares was defoliated, and arborists suspect this year will be just as bad. By comparison, the worst year prior to this was in 1985, when 380,000 hectares was defoliated.

What can be done?

The good news is that by now the worst of this year’s damage is nearly over. The caterpillars usually metamorphose into adult moths by mid-July. The adults focus all their energies on finding a mate and creating the next generation of caterpillars.

It’s not too late to wipe out some of those caterpillars before that happens, though, and also to trap the female moths (which can’t fly). The most effective way to control them is to wrap your tree trunks with a thin strip of burlap. You can see directions here.

The caterpillars and female moths crawl up and down tree trunks in search of shelter. A strip of burlap folded over itself will provide them with a shady place to rest, but also trap them. You then can go along and scrape the insects into a bucket of soapy water, which will kill them.

In late summer, it’s also worthwhile to go around those same burlap bands and look for sticky egg masses, which can also be scraped off and destroyed.

What about my trees?

If your trees have been attacked, don’t despair. As long as the trees are healthy, they will quite likely recover.

While gypsy moths are not native, native species like forest tent caterpillars do essentially the same thing — defoliating entire trees for a season or two, before their population collapses. Most trees have evolved to deal with this kind of attack, and a healthy tree can handle a year or two of defoliation without any long-term damage.

The best thing we can do for our trees now is to ensure they have all the resources they need to recover. The heavy rains of this past week are fantastic news — it’s much easier for trees to recover from the moth attack if they’re not also battling the stress of a drought.  If July and August are exceptionally dry, it’s a good idea to water your trees, even if you don’t normally do so.

Depending on the trees, you may also want to give them some fertilizer or a top-dressing of compost or mulch to ensure they’ve got all the nutrients they need.

After that, it’s partly a matter of waiting for nature to takes its course. If this coming winter is extremely cold, that will help — the eggs can’t survive extended exposure to temperatures below minus twenty.

Whether the infestation continues in 2022 remains to be seen, but it’s certain that gypsy moths are here to stay. All that we and our trees can do is learn to live with them.

Posted in In the Garden.