Mystery pests

I just did a bit more googling and another allotment site post said they had success controlling the weevils by boiling rhubarb leaves in water and using that to spray the affected plants.

That's pretty handy cos it looks like they are a problem particularly in April and May when peas are at their youngest and most vulnerable, and the rhubarb's in full swing too

Here's the post

It looks like the consensus is that growing peas to a good size in the greenhouse or at home before planting out means they are less likely to be totally finished off... But I'll be trying the spray personally.

I've been googling exactly the same thing - they decimated my Chinese leaf cabbage last year - our site rep says he thinks that the increase in oil seed rape has brought them in.
Covering plants in enviromesh or fleece seems the most common answer but no good if the blighters have found your plants already.
They overwinter in the soil so apparently a good hoeing of your soil in the autumn gets rid of loads of them but if your neighbours don't do this then it's little help.
I read an article that suggests using soft soap in water regularly helps. Another thing I read is boiling rhubarb leaves in water and using that as a bug spray.
I've been spraying all my crops every week with washing up liquid in water - it kills aphids and mealy bugs and touch-wood I haven't actually had any problems with flea beetles yet so maybe its helping those too....
Have you come across any remedies etc?

I have just bumped into a fellow plotter and he advised me that Pyrethrum is the component in Derris! I thought Derris had been banned but apparently they just stopped producing their insecticide after being unable to afford EU regulation testing...
At least the product is still out there I guess
Update - this isn't correct - Derris uses rotenone.