I have been unsuccessful with brassicas due to cabbage worm infestations. So this time, I decided that I will try something different.
I decided that instead of spraying every 7-14 days, I will install inexpensive row covers before the seedlings emerge and leave the on, the entire growing season.
This row cover cost about $15 to make and it covers a 4' x 8' area. I used 4 - 10' 1/2" PVC poles buried about 6" into the ground (we don't typically freeze here); 10 yards of tulle, and some clothes pins. I weighted down the edges with rocks from the yard and the carpet that I have placed between the rows (the carpet has pastic under it).
What's great about this is that the moths can't get in to lay their eggs! and I can switch out the tulle with some 2 mil or 4 mil plastic sheeting next month to grow throughout the winter (Zone 8a)! I made 3 of these this year.