i have flea beetle now on my cabbages,two things to try plant flowers near any cabbages etc african marigold are very good this year i have put sunflowers in as well which does help as well plus it makes the plot look nice,also you get use garlic and nettles,fill a bucket of water fill with nettles and chop up a clove of garlic let it soak for about three days outside,take out nettles and spray on you crops.let me know how you get on