In message , Stuart Meier
writes
I have been spraying to try to get a very bad infestation of woolly aphid
under control. Not sure it penetrates the waxy wool. Would it be worth
gently pressure washing it all off? Or any other suggestions?

The least environmentally damaging option is a stiff brush with meths on
which will kill all the ones you can wet with it. Trouble is on a big
tree it isn't easy to get every last one so you need to keep vigilant.

If you don't mind using nasty systemics then dimethoate will get some
control, but to eliminate them entirely you probably need several goes
and combine it with the meths treatment and/or soft soap contact
insecticides.

I suspect (but cannot prove) that ants harbour these things over the
winter so controversially a grease band may help prevent them. It
certain stops the ants from attacking the predators of aphids. Trees
with ants seem to have considerably more trouble from woolly aphid
infestations. YMMV

Regards,
--
Martin Brown