Question
I have a weeping cherry that is about 15 years old that is infested with
caterpillars. I sprayed it with BT ten days ago after blooming and the
beginning of the development of leaves. I still see the caterpillars moving
around. Did I spray too early? Can I do it again?

Answer
Bt works on caterpillars that feed on the foliage. The caterpillar eats the leaves with the Bt and this will kill the insect. They have to eat the foliage for the Bt to work. The younger the caterpillars are the better Bt works. I would spray again so that you get the spray on the new leaves. After spraying wait about 10 days and if there are still signs of feeding I would use another insecticide that will kill the caterpillar on contact. There are many that will work check with your local nursery for one for use on cherries.