Root aphids

Bought a conifer,Pinus Mugo, on Saturday. Come to plant it today and find it is riddled with root aphids. Anyone ever used a systemic insecticide on Conifers? Or, better still, washed the roots clean and the plant survived?
I know take it back and complain, but a 100 mile drive is not really economic!

 

I have been known to soak root balls in malathion to kill off ants that have built nests in pots, and its done no harm to the plant.
Cant think what you could use these days though.
If you give it a good soak then presumably a contact killer would work.