The favas are about 2 feet tall and flowering but I noticed the tips are covered by black aphids. Not unusual, but last year i sprayed with pyrethrin. This year before spraying again, I noticed more lady bugs on the favas than in years past. They are not covering the plants nor does it take much looking to spot one or 3 or more either. They seem to like the leaves as I do not see them on the stalks with the aphids. Will the pyrethrin kill the laby bugs as well or so I just let them do their thing? If so there does not seem to be enough of them to make a dent in the aphids. I am not new to gardening and am using primarily organic methods in a raised bed. I realize a solution is not overnight, but how long should I wait before attempting something stronger?