Q.Blight
I think I have a blight on my butterfly bush. How do I combat this?
This is a tough one as Buddleia is often problem free. First examine the plant carefully for insects. Insects that suck juices, like mites or 4 lined plant bug can cause a dead spot in leaves. Check leaf undersides for bugs and signs of downy mildew. Is the shrub in soil that drains adequately; it is susceptible to root rot in heavy clay or where hardpan is close to the surface. (I don't think root rot is the problem here.) If all checks out OK, then we are left with fungal leaf spot. Remove all the affected leaves that you find then treat the bush with an anti-fungal from your garden center. Treat tops and bottoms of leaves. Follow instructions carefully and keep an eye out for evidence the fungal disease is coming back. At the end of the season, cut the bush down to 9 inches and rake away all plant debris. Let's hope this results in a healthy plant next year. Make sure water Buddleia at soil level, not overhead. Consider thinning out some of the branches to improve air circulation. This lessens the risk of fungal disease.
