Roses are some of the most popular ornamentals for a good reason: They’re stunning. When they’re healthy, that is.
But if you grow roses long enough, you’ll inevitably run into diseases, and downy mildew is becoming a more and more common one.
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With its beauty-ruining dark spots and ability to turn a robust bush into a sad, stunted one, this disease isn’t one you can just ignore.
It also spreads like wildfire, and the pathogen that causes it is just as happy to feed on cane berries as it is on roses.
The more we can do to prevent, identify, eliminate, and otherwise get a handle on this disease, the better. This guide can help you do that!
Here’s what we’ll discuss in order to make that happen:
Most rose growers have encountered powdery mildew or black spot, but while downy mildew isn’t as common, it’s still a frequent problem that’s becoming more prevalent, and one you should know how to deal with.
Before we talk about that, let’s chat about what the heck causes this disease.
What Causes Downy Mildew?Downy mildew is caused by Peronospora sparsa, which is a pathogen known as an oomycete or water mold.
For a long time, scientists thought oomycetes were a sort of lower fungi. Now, they’re classified in a group all to themselves, and we know they’re more closely related to algae than fungi.
This group includes pathogens that cause some pretty nasty diseases like tomato blight, root and stem rots, and of course, many types of downy mildew.
Water molds, specifically Phytophthora infestans, are also responsible for the disease that caused the potato crops to fail in Ireland in the
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