Flea beetle

It is an absolute menace down here and I'm surrounded by forest with a bit of pasture, maze & sunflowers. The hotter and drier the worse they are.
I have tried fleece, but everything fried underneath, and diatomaceous earth with some success, but it is a blunt instrument that kills all soft bodied invertebrates. I have to protect my glow worms because they eat the slugs.
Growing everything brassica away from the veg garden in modules helps - somehow the little darlings have never thought to look around the side of the house! But my red russian kale, two good robust plants, have gone in a couple of days.
I only direct sow radish in the spring and autumn and no longer grow Pak choi at all as it really suffers.
Keeping the ground moist (40 degrees, hollow laugh) does help. That means watering three times a day ...
Today I sprayed all my brassicas with insecticidal soap and tomorrow I am considering going out with the cordless hoover!!
Hoeing isn't an option as I heavily mulch to conserve moisture and mostly no dig, the mulch of course may be providing overwintering habitat.
And this evening I heard them pinging off the horseradish as I walked past.