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Controlling LDD Moth (Gypsy Moth)

This invasive moth causes serious damage to Ontario trees

If there’s only one pest on the tip of everyone’s tongues this year, it’s LDD moth, also known as European gypsy moth. Controlling gypsy moth is important, because the moth caterpillars can quickly cause significant damage to trees and plants.

Though this moth has been commonly known by the name European gypsy moth, the scientific name, Lymantria dispar dispar, or LDD moth, is becoming more common to avoid the use of a slur in the common name.

LDD moth originally comes from Europe, but has been seen in Ontario for 60 years now. The province’s first major outbreak was in the 1980s, though more and more have emerged in recent years.  Outbreaks typically appear every 5-10 years and last 2-4 years. The current outbreak in 2021 is in its third season.

When Does LDD Moth Appear?

LDD moth caterpillar close up on tree bark

Caterpillars hatch from eggs in mid to late May. For the next 40 days, they eat everything they can. This is when the most serious damage to trees appears.

Each caterpillar consumes about one square metre of leafy material before forming a cocoon. Ten to fourteen days after cocooning, the adult moths emerge — normally late June to early July — and will breed and lay eggs.

Which Trees Does LDD Moth Affect?

Oak trees are the favoured tree of LDD moth. However, this pest affects over 400 different trees and plants. Other trees include sugar maple, elm, poplar, spruce, birch, willow, as well as some smaller shrubs and plants.

Most trees will recover from becoming a caterpillar buffet once, though you may be left with a nearly bare tree for the rest of the season. It’s when a tree sees repeated defoliations by caterpillars over several years that it can be fatal to the tree. Three years or more of caterpillar attacks can cause real damage.

For the most part, caterpillars aren’t interested in coniferous trees, unless they’ve already eaten everything else. Unfortunately, conifers have a harder time recovering from an infestation. Just one season of defoliation may kill the tree.

What Kind of Damage Does LDD Moth Cause?

Defoliation on a tree from LDD moth damage
Defoliation on a tree from LDD moth damage

Check out the images above to see the damage caused to one client’s tree by LDD caterpillars in just 48 hours.

A healthy tree may survive three to five seasons or more of caterpillar infestations. However, stressed or damaged trees can be more heavily affected. Oak trees can be particularly badly affected. A tree damaged by LDD moth can look as though it’s died, although it may have only lost its leaves.

Trees suffering from other infestations, fungi, drought, or breakage are more susceptible. The loss of leaves can cause excess stress to these trees and deplete their energy sources.

How Can I Identify LDD Moth?

Caterpillars are hairy, with red spots along their backs. Adult moths may be brown (male) or white (female). The females can’t fly.

LDD moth shouldn’t be confused with tent caterpillars, which create distinctive webs in trees. LDD caterpillars don’t create tents.

Tan egg sacs from the moths can be found everywhere if you have an infestation. These coin-size sacs can be found on the bark, on the branches, on the sides of buildings. Each female can lay between 100 and 1000 eggs.

How Do You Get Rid of Gypsy Moth?

Brown adult male LDD moth

One effective, but unpleasant, way to treat moths is manual removal of egg sacs. The masses can be scraped off trees between August and May, when caterpillars emerge. They need to be placed in a sealed container for two days, then put in the garbage. Scraping egg masses onto the ground won’t stop an infestation from recurring next spring.

Gypsy moth spraying is done from May to June. BTK, the pesticide used, must be applied by a registered pesticide applicator. Ideally, spraying is planned in the winter before caterpillars emerge. Spraying can be conducted on a single tree or for larger-scale infestations.

Arborists and pesticide applicators can also treat some trees with a systemic insecticide that can help protect the tree. This also needs to be applied in early spring before the caterpillars emerge.

Trunks can also be wrapped with material to gather caterpillars during the caterpillar season in May. Once they gather on the material, you can catch and dispose of them.

Keeping your trees healthy is an important step to prevent infestation and help the tree defend itself against infestation.

Natural Predators

Some native birds and animals in Canada eat LDD moth. Blue jays and orioles eat caterpillars, while chickadees eat egg masses. Some small mammals like mice, chipmunks and skunks eat caterpillars or cocoons.

LDD moth is also vulnerable to the caterpillar virus NPV, which kills them. The Toronto Regional Conservation Authority found evidence of this virus circulating around caterpillar populations in June 2021.

Precautions With LDD Moth

LDD caterpillars and egg masses can cause an allergic reaction in some people. It’s important to wear gloves when handling caterpillars or egg masses.

Conservation authorities and environmental agencies across Ontario and Canada continue to monitor infestations of LDD moth. With any luck, the current infestation cycle is nearing its end.

Vista Tree has helped many clients tackle an LDD moth infestation on their property! If you need help treating your trees from an LDD moth infestation or protecting against future infestations, give us a call!

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