How do you get rid of bag worms on apple trees?

[Reinbeau]

Look into Bacillus thuringiensis (BT).

This is excellent advice. I spray my weeping cherry tree with BT every spring, two weeks apart, the moment it stays over 45 overnight. This will take care of the bag worms, plus northern moth caterpillars (we have them bad around here), gypsy moth caterpillars, etc. It is a bacteria that causes them severe tummy aches and kills them.