Well the black fly won't actually harm the beans - you could give them a blast with the hose pipe or simply ignore them.

yes, and even if you have lots of beans set you can still pinch out the tips. You only need to spray if the fly has got well down the plant.

Sorry Snoop, we basically ignore blackly or blast with the hose... doesn't seem to have mud effect

thanks to all the reply on my black fly problem, from a complete novice, ill try pinching out the tops, let you know what happens.
thanks again from sunny Gower