Worms are eating my tree!

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

By “worms” you probably mean caterpillars. Don’t get too excited by all the holes in your tree leaves, because caterpillar feeding damage does not affect tree health until more than 30 percent of the tree canopy is removed, and 30 percent canopy loss means that one-third of every leaf has been eaten, or one-third of all the leaves are gone. That level of feeding injury is rare and usually only happens with occasional outbreaks of gypsy moth, eastern tent caterpillar, forest tent caterpillar, fall webworms, orange-striped oakworm, mimosa webworm and a few others. Most of the feeding damage that I have seen on shade trees this week has been caused by spring and fall cankerworms.

Cankerworms are caterpillars with only two or three pairs of fleshy prolegs instead of the standard five pairs of prolegs that most caterpillars have. This causes them to “inch” or “loop” when the walk, and is why many people call them inchworms or loopers. Cankerworms rarely cause enough feeding damage to hurt shade trees, and the same is true for a large group of caterpillar species that are often referred to as “spring defoliators.” Enjoy the inchworms and don’t worry about your tree.

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