It sounds like webworm damage if they are building webs in the branch angles of the tree. If possible remove the webs, doing this towards the evening hours when the caterpillars tend to be in the web and not feeding. Sprays work best when the worms are still small. Suggested sprays include Sevin, and Bacillus thuringiensis 'Kurstaki'. Spray the webs and areas around them. Follow label for mixing and applicataion directions.