I have Black Knight butterfly bush now for about two years. My bush been doing very well until two weeks ago. I have noticed brown spots on my bush leaves and some of the flowers are dropping, mostly on one side of the bush. We had humid weather conditions here in San Diego in the last couple of months. Thinking could be fungi, so I bought the spray thinking this would help. Also, water the other day which seemed to help. But now I'm getting some some of my red flowers turning white or pink colored. Should I keep watering or prune back the dead stem? Or should I wait later to prune back the bush hoping it will recover?
Black Knight Butterfly Bush
Certified GKH Gardening Expert
It does sound like a fungus, so you did the right thing. It may need some time to recover and you may need to retreat the plant if it is a tough fungus. You can go ahead and remove any brown and dead growth. This will also help with controlling the fungus.