The leaves on my climbing roses developed little black spots and now all the foliage has dropped off. What is this?
For questions on roses, I always go to the helpful experts at the Nashville Rose Society, and their Web site. It looks like there are at least two fungal diseases that cause black spots on the leaves of roses: one appropriately called black spot, and the other, anthracnose. You can tell the difference by looking at the edges of the spots. Black spot has the feathery margins, which give rise to some of its other names: leaf blotch or star sooty mold.
Both make a rose look really bad for awhile, which is why people who are serious about growing fancy, beautiful roses stick to such a rigid schedule of spraying. Fungicides are to ward off the ugly fungal diseases, pesticides to keep away chewing and sucking bugs.
Both blackspot and anthracnose overwinter on the plant and develop in the incubator of a cool, most spring. Cleaning up around rose bushes (getting rid of dead leaves and decaying matter), pruning out affected canes, giving the rose bushes plenty of air and reducing the amount of time water stays on the leaves can go a long way toward reducing the development of disease spores. Fungicides, applied on a regular schedule in early spring, can help prevent infection.
The problem of dealing with and preventing rose diseases is one reason landscapers and gardeners plant so many of the ‘Knock Out’ varieties, which bloom all summer and are resistant to most of the ugly diseases that plague garden roses.
Which leads to another question a friend asked not long ago:
Are ‘Knock Out’ roses real roses?
I understand the reason for the question, because it does seem impossible, doesn’t it? Given all that you hear about how you have to prune, spray and coddle rose bushes to get them to look their best, how can there be these easy-care upstarts, this ‘Knock Out’ series that seems poised to take over the rose universe? To get a rose expert’s view on the topic, I talked to Anne Owen, a Nashville Rose Society consulting rosarian.
“They are, in fact, a really true rose, in the genus Rosa,” she said. “The fact that they don’t require spraying for fungal diseases puts them in a category with very few others.”
Most rose enthusiasts, she said, like the challenge of growing the big, show-stopping roses – the ones in striking colors and with exceptional fragrance. And those are the ones that require coddling. “If you want a great big cabbage rose or a big hybrid tea, you’re going to have to spray.”
But a ‘Knock Out’ finds a place even in the most serious rose gardens.
“I think most rosarians have a ‘Knock Out’ or two because they are such great plants,” Owen said.