I have an apple tree (not sure of the type) that has had an issue with bag worms for the second year now. Last year I simply cut the limb and moved one. This year they attacked the top of the central leader - now what?
I use Malathion. You can buy it concentrated or diluted at Home Depot. Find their tent early in the spring and in the morning. Saturate the tent with the malathion spray and that will take care of them. Be aware that they lay eggs sacks on the tree branches. You'll want to look for those when the leaves are gone in the fall. The are 1-1.5" crystallized oblong casings that surround a branch. Spray those too and then watch for any tent activity in the spring.