The best material to spray to control the Tentworm Caterpillar, Eastern or Western, is Bacillus thuringiensis - Kurstaki which is sold under several brand names such as Dipel, Thuricide, or just BTK and sprayed in the first two or three weeks of the caterpillars life. The Eastern Tentworm caterpillars hatch from egg masses typically found on the target plants branches 9 to 18 inches in from the tips. These look kind of like someone tried to cover the branch with foam and those egg masses can be pruned off and destroyed.
If it is now too late for the BTK sprays very carefull use of Neem Oil or pyrethrine base sprays can also help. The same thing will help with Gypsy Moth infestations.

Tentworm caterpillars specialize on woody plants. On those plants, it's a periodic thing that won't kill the tree.

The only concern would be if the tree was young/small and recently planted. In that case you would want to disrupt the webs so that natural predators can get to the caterpillars.

The various forms of Btk won't work unless you disrupt the webby nests. Same goes for any other spray you want to try.

smwester, once those pesky caterpillars begin trekking around, far away from their 'home' tree, they won't live very long. I wouldn't spray them (or your plants) with anything but rely on the large number of natural control agents already in place.

Birds, various wasps, and a wide assortment of other predatory critters will soon find the caterpillars. They are also easy to hand-pick and toss where the birds can find them.

I have had the Eastern Tent Worm Caterpillar in my fruit trees, in the Chokecherry, in the Crabapple, and the trreatment of choice recommended by Michigan State, Ohio State, Purdue, University of Illinois, Clemson, and others is spraying with the Bacillus thuringiensis - kustaki sprays. This is also the treatment of choice for thje Gypsy Moth larva. It works, if you spray early enough in the larvas life. This same material will work with the Fall Webworm, the Western Tent Worm, as well as the Forest Tent Worm caterpillars.
While many times the damage done to affected trees can be mostly cosmetic repeated infestations can, and has, caused the untimely death of those trees. I have never had to breeak open the webs to get the leaves wet when spraying this material, and I do not see birds or other predators controlling them.

Here is a link that might be useful: About Tent Worm Caterepillars

It was said: "treatment of choice recommended by Michigan State, Ohio State, Purdue, University of Illinois, Clemson, and others is spraying with the Bacillus thuringiensis - kustaki sprays"

That works only if the cats eat leaves coated with the B. t. kurstaki, also if the cats are *less* than half-grown.

Golly, kimmsr. Breaking down the protective web/nest is critical to efficient tent caterpillar control. If you would do that (with a strong spray of water, a rake, etc.), you'd finally be able to observe the activity of birds, as well as predatory and parasitic insect activity. That very simple physical activity should come before the application of any product.

Outbreaks of tent caterpillers often coincides with the frenzied search by birds for food for their hatchlings. However, there are dozens and dozens of bird species that would love the easy pickins, if you'd only help out a bit. I think of robins at once because they are so plentiful in my neighborhood. But the Carolina wrens, chickadees, downy woodpeckers, cardinals, some assorted warblers, (and many others) can be seen collecting caterpillars from opened nests or from the ground....just from my back yard.