Do you know the difference between black spot and downy mildew? I am just now realizing I’ve been battling downy mildew. So not cool!
I get emails from many rose growers in spring and fall who think they have blackspot. Many of them have been treating for this disease and don’t understand why the fungicides they are using are not working. In most cases I find they have misdiagnosed their problem and what they actually have is downy mildew.
I will talk about how to control both diseases in future blogs, but for today let’s focus on what they look like.
Advanced stages of blackspot
Blackspot (Diplocarpon rosae) starts as a small black spot/spots on otherwise green healthy leaves. As the disease progresses, the leaves get more spots and the green tissue begins to be replaced with yellow. Usually within two weeks of infection the leaves will begin to fall and the entire plant may be defoliated. Left untreated the plant will try to put forth new…
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