There was an article in the Dallas Morning news just the other day about webworms. I was surprised that it didn't say to use some sort of nuclear chemical!!
Just MHO but I thik there are more of them b/c too many people kill wasps-the webworms' chief predator.
Best thing to do is remove the ends of the branches that have the webs. If you don't want to prune a large branch, poke holes in the webs or if they are too high, throw rocks til you penetrate the webs. Birds & wasps will be there in a short time to eat 'em.
You CAN use Bt-it's considered 'natural'.
I'm assuming that trichogramma wasps-set out in the spring-will also prevent webworms. (but since I AM the 'trickygrama', I like to recommend them.
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Patty