There is a Bt that is specific for moth and butterfly caterpillars which is what I use in the organic garden I manage. The one I use can be used up to the day of harvest. And it is fairly effective if you spray regularly. They eat the bacteria that you've applied to the plant, stop feeding soon after, and die. Pretty safe biocontrol that doesn't really have much negative impact on people since it's a bacteria specific to moth and butterfly caterpillars .