Posted: 07/03/2012 at 23:16
I think I've found the solution to blackfly on runner beans - do nothing about it.
The plants get swamped with blackfly and this definately inhibits growth - effectivelt knocking them back a month.
Then the ladybirds arrive, quickly followed by their grubs (I've counted 20 on one plant).
The blackfly dissapear, the plants recover and I get a great crop.
I've been experimenting with tying bundles of bamboo sticks within the plants to provide a nesting place for the ladybirds. At the end of the season these go into the greenhouse, and I tie them back onto the canes at the start of the next year. I have no idea whether this has any effect - but I certainly get loads of ladybirds.
Sadly this doesn't seem to work on broad beans - the blackfly seem to win this battle.