New brassica pest
The past 3 summers my broccoli and kale leaves have been turned to lace by a new (to me) moth/caterpillar. Looking for an organic killer that works more efficiently than squishing with fingers. Bacillus Thuringiensis has little or no effect. Photo of the beast below.
Livingston County Michigan
That is the cross-striped cabbageworm.
I had them too across about 20 broccoli plants. I used the leaves to squish them all until they popped. The ones that got into the broccoli heads were uncontrollable.
Bt should work on the small caterpillars. But the bigger they get the less it works. The same can be said for other organic insecticides, like pyrethrins or spinosad, or any oil/soap. You may need an integrated approach of soaking the plants inside and out with a spray for the little ones that are hard to find, then following up with manual squishing for the ones that are not killed. Remove your plants as soon as you are done with them and till in the late fall to disturb them from their overwintering positions.