does BTK work; if so, when should it be applied?

The flower and leaf buds on my apple tree are beginning to come out however I notice that many are showing obvious signs of distress. When I pry open the buds, I find tiny quarter-inch long green caterpillars. Have read elsewhere that the infestation can be treated with Bacillus thuringiensis kurstaki (BTK) ... am wondering if anyone on the forum has had success with BTK? If so, when is the best time to apply it? And finally, does it matter that the bacterium will probably not be applied directly on the caterpillars as they are hidden within the leaf/flower buds?

 

I haven't used BTK myself, but I understand that the bacteria must be consumed by the caterpillars to be effective. It is not a contact poison. It can be applied any time there is vegetation being eaten by caterpillers, but you should avoid using it during rainy weather.

 

… thank you for the reply. I applied the BTK using a hose-end sprayer. Of course, I wondered, given what I'd read, if that was the right tool ... and then, did I mix it correctly … and was it the right applicator dial setting as such a small amount seemed to be coming out. One good thing: the weather stayed dry for 48 hours altho it is raining today.