Looks like a fairly severe case of aphids. You can kill them with alcohol or soapy water but I prefer to use an organic pesticide with spinosad as its active ingredient because of its residual effect. And if you have aphids cabbage loopers are not far behind and spinosad takes care of them too.
Oh my gosh, I have the same problem! I was specifically looking for answers on these bugs and what to do about them. So glad for the advice from the more savvy gardeners out there!
Crucifer Flea Beetles (Phyllotreta cruciferae and other related species) are small black Flea Beetles (Alticini, Chrysomelidae) known to feed on many members of the Crucifer Family (Brassicaceae), including cultivated species of Brassica, such as Cabbage, Broccoli, Kale, Turnips, etc.
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.