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My 12- to 15-year-old Diablo Ninebark shrubs have had downy mildew for 3 or 4 years. Each year I prune branches out that have mildew. I disinfect my pruners between cuts, clean up as much as I can around the bushes, and throw all the leaves and branches in the garbage. The problem becomes more severe each year. These bushes get lots of airflow around and through them. I'm keeping the centers open for air flow.
I am wondering if I can give the bushes a hard pruning this spring before they leaf out, and if that will help control the mildew. How far down can I prune them -- is a foot from the ground too much? Or would I be better trying to control the problem with a fungicide. My thought is that if I get rid of as much of the mildew as I can, I would have an easier time controlling it with a fungicide. I have not yet used a fungicide.
Richland County ND Posted 3 days ago