I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
Most of the time worms in a tree are not numerous enough to warrant spraying. They just don't threaten the life of the tree. However if they happen to be really bad or if you just can't stand having them around you can spray the tree's foliage with a product containing B.t. which is a low toxicity natural control for caterpillers. If your "worms" are the webworms then they do cause significant damage and can be controlled by the same product IF you can get it inside their webs. Take a pole and tear up the webs before spraying the foliage.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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