How to Prevent Black Spot on Roses and Treat Roses with Black Spots

Be sure the rose disease is blackspot by learning what black spot is, what its symptoms are, and how it spreads. Diplocarpon rosae is a fungus that infects roses by causing the leaves to develop brown to black spots. These spots, which can be on both sides of the leaf, start out small roughly round dark areas. Later yellow rings will form around them. They will enlarge and eventually cause the entire leaf to turn yellow and brown or black before falling off the bush. This rose disease can totally defoliate a plant over a short time and even cause lesions on the green stems. The plant will eventually die becoming weaker from constantly losing leaves. Being a fungus, black spot likes wet humid weather and starts growing when the temperatures hit 75 degrees and moisture is present for 7 hours or more. It forms spores that are spread by air movement and water droplets as they splash or run off of the infected plant parts. When conditions become too dry or too cold the spores become dormant, hiding in dead plant materials and diseased canes. Black spot spores do not over winter in the soil.

Use preventative measures to stop rose problems before they begin. Clean up the rose garden every fall, raking up all fallen leaves and clippings. Do not compost the gleanings which may contain blackspot spores, instead either bag them to be hauled away or burn them. Before growth starts in the spring spray the plants with fungicidal sprays such as wettable sulfurs and copper based solutions labeled for use on roses. The use of sulfur to fight black spot is well known and proven. The spores won't grow on sulfur but because it washes off you must repeat the application on a regular basis and after each rain. Keeping the leaves dry is another preventative practice. Don't water from overhead instead use drip or soaker hoses to water the soil under the bushes. Space the plants to allow for good air flow around each, at least 3 to 4 foot apart, so the leaves will dry quickly after rains. If the disease is seen starting, clip all affected leaves off and trim any infected canes back to two healthy buds then dispose of all infected materials. Prevention is far easier than stopping the rose disease once it has infected the rose plants.

Follow a regular schedule of using home made fungicidal sprays or commercial products to fight the black spot disease. Make a rose calender showing the days that the roses should be sprayed and stick to it even if there are no signs of rose diseases. Make a rose spray using baking soda and dish soap. Mix 1 tablespoon of baking soda and a teaspoon of mild dish soap, like Ivory, in a gallon of warm water. Spray this on the roses every 7 to 10 days, thoroughly covering the top and bottom of all the leaves, and stems. This will also help with aphids and mildews. Neem oil is another good organic treatment for fungal rose diseases and some insects. Just use it as directed on the label and reapplied every one to two weeks, especially during wet periods. There are many good commercial products on the market that will control black spot and can be used after the disease is advanced. Some of the better known ones include: Ferti-Lome Halt Systemic, Sporan EC, Spectracide Immunox, Captan 50 WP, Kop-R-spray, Orthro Funginex, and Bayer Advanced Disease Control. Many of these are highly toxic and some require that no one re-enter the sprayed area for an extended time. Read and follow all instructions on the label when using them. There are dust products for fungus treatments but the liquid treatments work better.

Keep rose plants healthy and strong. Healthy plants are less likely to die from black spot and also seem to get over it quicker. Plant roses in full sunshine where they don't have to compete with other plants, especially trees. There are some companion plants that help roses to thrive such as chives and garlic. Feed roses and grow them in good soil. Have the soil tested to see what minerals it might be deficient in, if the pH needs to be adjusted, and how much fertilizer may need to added. Read up on roses to find out what kind of soils they prefer. Manure tea is a great way to feed rose plants and if sprayed on the leaves will actually fight black spot fungus.

Grow resistant variety of roses. Some types of roses are more resistant to black spot than others, but because the fungus is always evolving and changing each season, some of the older resistant varieties such as Peace are now susceptible to the fungus. There are listings on the web of resistant rose varieties, here are some that I know of: Miss All-American Beauty, Mister Lincoln, Nantucket, New Day, Angel Face, Betty Prior, Bill Warriner, Bonica, Harrison's Yellow, Katy Road Pink, Knock Out, Mrs. R. M. Fincn, Prairie Harvest, Prairie Sunrise, Robusta, Sea Foam, Simon Fraser, Simplicity, Sir Thomas Lipton, The Fairy, Wanderin' Wind, and the Rugosa roses. Rugosa roses are normally resistant to black spot disease. Remember these varieties are resistant to black spot not immune to the plant disease. The fungus can develop into a new strain during any season so there is still a need to practice prevention methods and always keep an eye out for black spot on roses.
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