Insecticides are most effective for the smaller life stages of spongy moth caterpillars. Bt kurstaki, and contact insecticides with one of the following active ingredients may provide relief: carbaryl, cyfluthrin, cyhalothrin, cypermethrin, deltamethrin, permethrin.

Systemics would have needed to be applied a few weeks ago. Even if a systemic were applied tomorrow, it would take time for the product to move within the tree and by the time it's flowed to all parts, the caterpillars will have already reached adulthood.

If your trees are more than 10-15 feet, its unlikely that you'll achieve good coverage without aerial spraying or an arborist who has the correct equipment to have the insecticide reach and kill the caterpillars that are high in the foliage.

See here for additional information: https://fyi.extension.wisc.edu/spongymothinwisconsin/pest-management-2/management-guide-for-homeowners/