Every year I dread having to fight flea beetles as they pin-hole my arugula, mustards and radish plants. I've tried spraying them with a rotenone/pyretheum insecticide...barely fazed them. Someone suggested beneficial nematodes, and I tried them, but maybe got them in the ground at the wrong time. It has been a couple of years since I addressed this problem, so maybe someone has discovered the answer now.
Just a quick google:
Flea beetles can live where their preferred crop was last season, so rotate crops. Then the flea beetles may live over outside the vegetable area.
Put row covers over the susceptible crops immediately on planting. Flea beetles that have over wintered outside the bed cannot then move in on the crop. Once they are there, row covers do not work.
Plant something flea beetles like near but outside the vegetable beds. Flea beetles will come to that trap crop and can be sprayed with something stronger that you might not want to use on the vegetables.
I think I have this bug,but not positive.It's small,black.and it hops.This is the first year they have been in my veggie garden and they have wreaked havoc.They have been all over basically everything in my winter garden,on my turnips,cauliflower,beets,lettuce and allysum.I sprayed repeatedly with neem and that made no difference.
Do they leave little pinholes in the leaves of your affected plants? That's a sure-fire indication of flea beetles. I'm gonna try introducing beneficial nematodes into my garden beds just before the beetles hatch. The nematodes are sposed to dine on the beetle larva. I'll also use row covers, pyrethrume spray and sticky traps. It's all out war this season...hope I win!