Diseased trees - felling, need containment?

Asked June 16, 2019, 9:08 PM EDT

I have two trees that are clearly infected for years with little worm looking squiggles. What is it and do I need to contain the disease when the trees come down?

Wayne County Michigan insects

3 Responses


Those are slippery elm pouch galls caused by the aphid, Kaltenbachiella ulmifusa (Hemiptera: Aphididae). They may be unsightly but they do not harm the at all. They do not live on other tree species, only on elm.

These abnormal growths are caused by an aphid that has a very interesting life cycle which involves two host plants. During the first part of the summer the aphid causes galls to form on slippery elm leaves and then later on, it feeds on the roots several members of the mint family. The insect overwinters in the egg stage. The egg hatches early in the spring into a stage called a fundatrix, a.k.a. stem mother. The stem mothers begin feeding at or near swelling leaf buds which causes a small pit to form around them. By mid May, the stem mothers are completely enclosed by green gall tissue. The gall is fully formed by late May. While the gall is growing, the stem mother fills it with hundreds of offspring. These reach maturity, complete with wings, around the end of June. The galls then split open and the winged females emerge and fly off to their alternate hosts in the mint family where more eggs are laid. Both males and females hatch from these eggs. When mature, they fly back to slippery elm, mate and the females deposit single eggs in bark crevices. All this has taken place in approximately two months time. No further development takes place until the following spring when the eggs hatch and the new stem mothers start the cycle again.

Normally, leaf galls have very little effect on the health of the tree so chemical control measures are not warranted or recommended. Large numbers of galls can effect the appearance of the tree however.


I’m cutting these two trees down because we are putting in a fence and I could barely tell what kind of trees they are from all of the galls. When the trees come down, are they a risk to other elms in the area?


Probably not, if the others were going to get them, they would've got them by now.