Bacillus thuringiensis var. kurstaki (Btk) is a naturally occurring soil bacteria which is ideal for controlling nearly all types of caterpillars. It is highly specific in that it only harms caterpillars and has little effect on other species. For situations where large numbers are consuming your plants, this is a safe and effective insecticide.

It works by killing any caterpillar that feeds on the sprayed leaves. Any other insect that feeds on the same sprayed leaves will not be affected. Animals which consume a dead or dying caterpillar will also not be affected.

Consider spraying Btk on the leaves of an affected plant only when there is significant leaf and/or stem damage that goes beyond what is reasonable to control by hand picking. Btk should not be used as a preventative treatment as it breaks down in sunlight within 3-5 days and can be washed off the leaves in heavy rains.

Before spraying, be sure to thoroughly read the application guide attached to the insecticide container. Do not exceed the application rates and frequency and only spray in optimum conditions.