Several sites recommend 3 qts insecticidal soap mixed with 1 qt water and brush treetrunk but I think you also could spray it on. Read label well, wear gloves, old long clothes, mask, hat & goggles. Keep children & pets away until this is dry....The caterpillers climb down & up the tree........this will kill them.............if you see any moving you could put them off and drop them in a bucket of hot water & soap....and then flush it later. I have used that handy grey tape and turned it so that the sticky side is out and went around the tree.....I had to have someone help me.....I kept catching a tip of the one that I put around and made it 3 to 6 inches wide....and they stick to this. In the fall when all the leaves drop off, we use dormant oil according to directions for the walnut...............then again in the spring.......up to the bud...............when the bud opens then I only do the trunk...........read the directions well as there is a heavier measurement for fall and a lighter measurement for spring................