Yellow sticky traps or counting the numbers of beetles you see on plant leaves will let you know if you have a flea beetle problem. Two beetles on a young plant of three leaves or less is the maximum or 5 on a plant with four or five leaves are the maximum that you want to see, otherwise you are over the threshold of what your plants can tolerate.
Flea beetles are most active in spring and especially love eggplant, potatoes, peppers, tomatoes, spinach, melons, and young plants from the cabbage family: broccoli, Brussels sprouts, cauliflower, cabbage, collards and kale. The cabbage family of crops of Asian origin are also favorites of the flea beetles for the lack of oil on the leaves, making them easier to hold onto and munch. If you like Chinese cabbage, tatsoi, mizuna, turnip, mustards, bok choi, radish, arugula or red Russian kale, then you need to think about how to protect your crops.
There are many organic pest control methods that work to prevent or decrease flea beetle populations, such as trap cropping, delaying planting until after the overwintering beetles have emerged (thus reducing their food supply and decreasing the population), insecticidal soap, neem, natural pyrethrin, kaolin clay (Surround), pesticide containing spinosad (Entrust), hot pepper or garlic sprays, and nematodes. Nematode formulations can be applied to the soil and attack beetle larvae reducing the numbers of adults that will increase the next cycle of adult beetles. Nematodes are usually available at garden centers. The native braconid wasp is another natural control, where the wasp uses the beetle as a host, thus sterilizing the female wasp while developing, and kills her upon its emergence. By using a commercial insecticide like Sevin to wipe everything out, the braconid wasp is also killed. Hence the beauty of organic gardening – balance is desired.
However, floating row covers may be the best protection. But a word of caution when using floating row covers – these are best used where no susceptible crop was grown the year before, otherwise you’ll trap the insects in with your food as they emerge from the soil. Be sure that the covers are continuous and securely covered by placing soil around the perimeter of the cover to keep it firmly sealed to the ground.
actually, these little bugs are kinda pretty!
After weeding replace the floating row cover ASAP. If you do find a few beetles after a few days of re-covering, control them with one of the organic methods listed above and then re-cover. Check back a few days later, as organic management of a garden is about control, not complete massacre.