Different Bt's work on different species and must be applied daily, preferably in the evening as sunlight breaks it down in under 24 hours. it is a pest specific 'cide and does not work on all leaf eaters by any means.

I find that Spinosad works on just about any worm including bag worm. It's a by-product of Rum distilleries and I believe Green Light's version is certified organic.

If your Bt was exposed to cold temperatures (I have Bt concentrate), will that render it useless?
Thanx!