[Stringbags]

I have 4 gooseberry bushes in 12 inch pots waiting to go into a fruit cage when I build it. For 2 years they have been devastated by sawfly, I repotted them washing off the roots and dumping the compost just in case there were lava in the pots ( they were gifts from other plots on the allotment) the one that I have in the ground is fine.Can anyone recommend a systemic bug killer that will be effective against sawfly or any other info?

Stringbags

[ptarmigan]

https://www.nematodesdirect.co.uk/nemasys-fruit-veg-protection/10-nemasys-grow-your-own-nematodes.html

I haven't used nematodes for sawfly - but the vine weevil nematodes worked really well for vine weevils.  Probably a good time of year to use it as well.   

With a sawfly infestation on a tree I have - I just picked them off systematically - this year they were hardly a problem at all.  So with what you've done and some nematodes that might work quite well?