Root aphids - nematodes?

[Inastate]

I've got a root aphid infestation, which I'm thinking is probably why my chilli's are yellow and not growing.

I found thousands, and the chalky substance they excrete, in my lettuce roots.

Has anybody successfully dealt with them? And can anybody reccomend good nematodes available in the UK? Cheers

[Bill HH]

I get them in my lettuce and the only control I have is by growing the lettuce on the other side of the garden and usining the affected bed for something else. I planted onions in that bed this year and they were not infested.