Communities are battling back with aerial sprayings to halt the defoliation of oak trees while homeowners try to kill caterpillars using everything from power washers to pesticides.
It is important to destroy the insect’s egg masses before they hatch between late April and mid-May, said Vic Foerster, an arborist with West Michigan Tree Services of Grand Rapids and vice president of the Arboriculture Society of Michigan.
‚”Each egg mass destroyed probably eliminates 400-500 caterpillars,” Foerster said. ‚”The cushiony, velvet-like tan-colored egg masses are about the size of a quarter. You see them on tree bark, buildings and in protected areas.”
Crushing and tearing apart egg masses is not enough, Foerster said. ‚”Dump them in a bucket of soapy water and let them sit a couple days to ensure eggs don’t survive.’
Recent outbreaks of the leaf-munching caterpillar have been reported in Michigan, Wisconsin, Minnesota, Ohio, eastern Canada and California.
‚”The insect’s favorite food is oak leaves, but it will feed on many other tree species such as birch, crabapple and willow,” said Bill McNee, a gypsy moth suppression coordinator with the Wisconsin Department of Natural Resources.
The caterpillar is native to Europe and Asia and was originally brought to the United States in the 1860s for breeding experiments in Massachusetts.
Gypsy moth caterpillars usually start to hatch between May 10-May 20 ‚”but you will not see them initially until they start to feed on leaves,” Foerster said. ‚”By June, you’ll know they are there. The greatest feeding damage is done by older caterpillars during the last two weeks of June, sometimes making it appear as if trees are stripped of leaves practically overnight,” Foerster said.
‚”The good news is they might defoliate the oak, but if it is a healthy oak, it will not kill it,” Foerster said. ‚”If you have a tree that is stressed for whatever reason, you defoliate it in spring, you could see it dying.”
Starting about May 10, homeowners can spray smaller trees with Bacillus thuringiensis, or B.t. for short — a naturally occurring, soil dwelling bacterium available at garden centers.
‚”You need to do this preventatively,” Foerster said. ‚”If you wait until you see the big caterpillar, the B.t. is ineffective. Get them at the immature stage after they first emerge.
‚”A downside to B.t. is the narrow window of effectiveness, but it does work and it does slow them down,” Foerster said. ‚”It’s one of the small victories we’ve had in actual biological control that is very effective.”
Caterpillars can be trapped using bands of sticky tape. Wrap a belt of duct tape 4-6 inches wide around the tree trunk about chest high and coat the band with a sticky horticultural pest barrier available at garden centers.
Banding materials are available from The Tanglefoot Co., including Tree Tanglefoot Pest Barrier and Tangle Guard Tree Banding Material.
Be sure to clean or replace sticky tape once it is laden with caterpillars ‚”otherwise, caterpillars will make it up the tree by crawling over the ones stuck to the tape,” Foerster said.
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