Driving back from Detroit last weekend, I saw several trees infected with tent caterpillar nests, and believe it or not, we have them in Rock County, too. So if you see that white webby mass in the crotch of a tree branch, they’ve found a place to call home.
Usually they prefer apple, crabapple or plum trees as a food source. You don’t have to get real radical like cutting the branch out. Just wait until evening or early morning when the worms are in the “tent” and pull the mass out of the tree.
The caterpillars go into the tent for protection at night and come out during the day to feed on the leaves. As their feeding range increases, they increase the size of the tent because they are getting larger too.
One moth lays this egg mass, producing the crop of hungry, fast-growing caterpillars that will defoliate a tree branch in a few days. Several tents in a small tree can strip all of the leaves, resulting in the death of the tree. And considering that each of those worms becomes another moth to lay another egg mass is reason enough to eliminate them.
If the tent is too high to reach, you can spray them with an insecticide, but do that during the warm part of the day when they are feeding. If they are in the tent, they are protected from the spray.
This is also a good time to spray garden phlox to prevent mildew (white powdery spots on the leaf), and black-eyed susans (goldstrum rudbeckia) to prevent septoria leaf spot (black leaf spots).
Notice that I said “prevent” ... much easier than spraying to cure! The fungicide I recommend is Daconil, which also is an excellent product to prevent the common blights on tomatoes.
The more recent introductions in garden phlox like the flame series are much more resistant to mildew than some of the older varieties. And while I am talking leaf spots, if your peonies have been plagued by diseases causing deformed flowers or spotted leaves, this same fungicide will help prevent that problem, too, if you apply prior to symptoms appearing.