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Thursday - July 14, 2011

From: Deerfield, WI
Region: Midwest
Topic: Pests, Trees
Title: Tree with brown spots on leaves containing caterpillars
Answered by: Nan Hampton, Eric Beckers, and Mike Quinn


We have a new little tree we planted in our yard and I went over to admire it and on each leaf there is a brown spot in which little worms are living. They are alive and moving around in the pocket the brown on the leaf has made for them. I showed my husband and he immediately cut the tree down and burned it, but I've never seen anything like this before and I'd like to know the name of the tree disease.


Technically, your tree's problem was an insect infestation, not a disease.  I consulted with a tree expert with the Texas Forest Service and an entomologist and both agree that your tree was infested with insects called leaf miners.  The little worms you saw were the larvae of the adult insect.  The adult female insects stick their ovipositors through the surface of the leaf and lay their eggs there.  The tiny larvae hatches and feeds on the leaf tissue layer between the upper and lower surfaces. The insect might be a moth, a beetle, a fly, a wasp, etc.   If you had told me what kind of tree it was, I might have been able to be more specific as to what kind of insect the culprit was.  Here is information about oak leafminers, the birch leafminer in Wisconsin, and the spotted tentiform leafminer from Wisconsin Master Gardener Program.  Wisconsin also has problems with leafminers in agricultural crops—corn blotch leafminer, vegetables, and alfalfa.  For mature ornamental plants the leafminers' effects are mostly cosmetic and don't usually severely damage them.  They can survive considerable leaf loss, but it may affect their vigor and make them more susceptible to other insects or disease.  Here is an article on controlling leafminers from Planet Natural and one on controlling birch leafminers from the University of Minnesota Extension Service.

By the way, our tree expert said that your cut tree could possibly, given the rainfall you receive, resprout from the roots (if your husband didn't dig them up) and grow up to be perfectly fine.




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