Some one on the allotment site swears by boiled Rhubarb water. Claims it
to
be a good poison. If so any one know the mix please?

Ged,

Rhubarb leaves contain oxalic acid which is poison to us so I suppose it
might kill blackfly if it's in the water in which the leaves were boiled.

Peanuts in a container near the broadbeans that only one bluetit can eat
from at any one time is also good for helping to keep blackfly down - the
birds queueing up "do the rounds" looking for something to eat.

It's also a good idea to kill off any ant's nest near the plants for ants
are the main cause for spreading and protecting blackfly.

Regards

Ron