These small insects surround themselves in a gob of froth or foam , resembling spittle. They feed by sucking plant sap. While they may feed in fairly large numbers the only control necessary is physical removal. A forceful jet of water usually works quite well to control them or an application of insecticidal soap is quite effective. Their damage is generally minor but they can cause significant damage if feeding in large numbers.
Typical damage is skelotonization of foliage .
Cankorworms can be controlled by using typical orchard sprays on apples or with B.t. products, carbaryl or malathion . These dark colored caterpillars have a blue strip down the side of the body . Chemical treatments at this point are not as beneficial as they could have been a few weeks ago, since most of the damage is already done. Carbaryl would be the best choice at this late date. If you shake the branch, a cloud of yellowish pollen will be produced.