You could use floating row covers as soon as you plant.

Since the brassica family does not need any pollinators Floating Row Covers can be a very good method of control for the various insects that do bother these plants.

This year I used floating row cover. Since I live in zone 7 the bugs over winter in the beds and came up under the row cover destroying the crops. I'm not looking for answers about how to grow brassicas in a pest infested area but what else I can grow. thanks

There are a vast array of lettuce crops, more and more on the market all of the time. Beet greens are another option and a favorite of mine. You may want to consider spinach and chard, as well. I'm certain that there are many more to consider...a quick internet search would probably be very helpful.

If I were to conduct such a search, I'd use 'leafy vegetables' or 'leafy green vegetables' or similar to direct the hunt for information.