Kay Easton wrote:

Stick the plant out in the rain for a few months, and, if that doesn't
work, throw it away. I long since lost the battle.

Some plants are magnets for rsm.

I suppose growing the same individual plants for 15-45 years all together in
the same
greenhouse is asking for trouble.

I'm wondering about using the biological control in the greenhouse.

It works provided it is warm and humid enough for them to breed up. The
greenhouse needs to be pretty well clean of insecticide traces though.
Predators otherwise get killed by eating too many poisonous prey.

They tend to go into population balance with some oscillations so that there
is a small residual infection but not enough to scar leaves too much. They
don't overwinter as well as the rsm so you may need to restock. And in really
warm summers they go off out of the greenhouse in search of better pickings
after they have devoured most of the rsm. That was my experience YMMV

Regards,
Martin Brown