Brassica flea beetle

Anyone else having a problem with these b*****a?  They have decimated all my leaf crops for stir fries (mizuna, red mustard etc) and rocket, have used so e stuff that was supposed to sort them out for the season, but no, back with a vengeance.  Any advice?

You'll have to tell us which one now 

PY insect killer powder.

Mine are covered with environmesh and they are still ruining them!  Think they are in the soil, so all I am doing is providing them with shelter......

I'll add rocket, pak choi, chinese cabbage to the list.  You name it, they'll eat it.

Good question Snoop. To date I have only applied it once about three weeks ago - and last time I looked they had not come back.  The swede are growing under netting and it maybe that the flea beetle were
 already in the soiling - lurking - before the net went up. The three weeks also means that the swede seedlings have really got established now - and even if they get a bit of damage now I think they will grow through it. In any event they look a lot better than last years.