BT for Hornworms

[kwselke]

I've spent the last two days trying to find the hornword that is chewing up the leaves on one of my plants and leaving nasty looking droppings all over it. This morning I decided to go biological on it and bought DiPel brand BT powder. I came home and dusted the plant and hollered 'Come and Get It'. Now an hour later it's raining. Should I redust after each rain or will the BT in the powder stick to the plant as a liquid form of BT would.