Using Natural Insecticides
Tent caterpillars are vulnerable to insecticides only while they are still moving around and eating leaves and other plant parts. Spray the affected plant thoroughly with a product containing the beneficial bacteria . Bacillus thuriengensis (BT) when the caterpillars are actively feeding. This will likely be sometime between March and April, depending on where you live. The caterpillars eat the Bt along with their usual leafy meal. When they ingest the bacteria, which harms only caterpillars, they sicken, stop eating, and die within a day or two.

For effective control you need to time the application fairly carefully. For best results, spray once and then repeat 10 to 14 days later. Spray initially in March or April , when the leaves are about half to three-quarters open. Because Bt washes off with rain, reapply it in 10 to 14 days to be sure you control the problem. Two sprays will generally be enough to keep the tree from being defoliated. Read and follow label instructions for use, storage, and disposal of this product, as with any other insecticide. If the tree or shrub is very tall and difficult to reach, hire a professional arborist to spray the tree properly and safely.

Click Here for more information on Using Bacillus thuringiensis

Using Synthetic Insecticides
The pyrethroid class of insecticides are effective in controlling tent caterpillars, but you again must use it early on in the season when the caterpillars are wandering around the tree or shrub munching on the young leaves. Go to Yardener's Tool Shed to check out the options in the Synthetic Insecticides section.