Caterpillars

Garden Clippings – July 1, 2017

It was a week or two ago that I heard a CBC News clip covering the unprecedented infestation of caterpillars in Manitoba, particularly around St.Lazare, near the Saskatchewan border. Apparently in some cases trees were completely defoliated by a multitude of hungry crawling creatures. People were removing them by the shovelful.

Earlier this week at a Garden Centre Group Co-op meeting in Winnipeg, I decided to see for myself. Unless I was told, I would not have known about the influx of caterpillars.

According to Sarah, a Parks Canada student who I met on the job near the river forks, the area around Winnipeg was largely spared. Furthermore, any trees that were damaged have already put on new growth with new leaves growing on limbs that were previously eaten.

Caterpillars are not a new phenomenon in Manitoba or anywhere in Canada. The most prevalent leaf eating insect in North America is the Forest Tent Caterpillar, although there are hundreds more that need leaves to survive.

Caterpillars’ normal lifecycle goes something like this: In mid to late summer an adult moth lays eggs on the twigs of a favourable host. Eggs hatch early in Spring. A month or two after which the caterpillar spins a cocoon. In a week or two the cocoon morphs into an adult moth. During the brief adult stage damage is minimal. Later in summer the female moth lays eggs and the cycle begins for another year.

This years caterpillar out break in Manitoba was not unexpected. Outbreaks usually occur every decade or so and will likely continue for a few years.

Damage ranges from small pieces to eaten to the entire defoliation of the tree. Damage is usually most severe high up in the tree.

Generally, trees sustain little long-term damage after caterpillars have had their feast. Many trees have a built in second set of leaves that can be pulled out if necessary. It is only after a few consecutive years of damage that a tree will show permanent damage, likely in the form of twig dieback and a general decline in health.

Control measures for caterpillars is usually not warranted. Many will die on their own due to lack of food. High temperatures and drought will also serve to keep the critters at bay. Parasites will also reduce populations.

Many birds, insects and small animals will have a heyday eating caterpillars, this ensuring their own survival.

In home landscapes, caterpillars can be physically removed with a long stick or rake. A t entomology class many years ago we were taught that removing the home of the tent caterpillars will put an end to their lives. A blast of cold water with a pistol nozzle or power washer may also do the trick.

If spray measures are warranted, environmentally friendly insecticidal soap, pyrethrins, diatomaceous earth and Bacillus thuricide will provide good control. A light infestation might be taken care of with a solution of soap and water.