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

Seeing your beautiful roses attacked by black spot disease can be disheartening. There are ways to prevent and treat the fungal disease known as Black Spot. By using the right products, following a treatment program, and knowing a few rose growing tips, you can beat black spot and have beautiful healthy roses.

Difficulty: Moderate

Instructions

Things You'll Need:

• Baking soda
• Neem oil
• Rose Fungicides
• Drip or soaker hoses
• Hand held sprayer

1. Be sure you are treating the right disease 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.

2. Use preventative measures to stop the problem before it begins. Clean up your rose garden every fall, raking up all fallen leaves and clippings. Do not compost the gleanings, 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 you do see the disease 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 disease once it has infected your plants.

3. Follow a regular schedule of using home made fungicidal sprays or commercial products to fight the disease. Make yourself a rose calender showing the days that the roses should be sprayed and stick to it even if you don't see any signs of disease. You can make your own 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 your 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 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 you don't re-enter the sprayed area for an extended time. Read and follow all instructions on the label when you use them. There are dust products for fungus treatments but the liquid treatments work better.

4. Keep your roses healthy and strong. Healthy plants are less likely to die from black spot and also seem to get over it quicker. Plant your 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 your roses and grow them in good soil. Have your soil tested to see what minerals it might be deficient in, if the pH needs to be adjusted, and how much fertilizer you may need to add. Read up on roses to find out what kind of soils they prefer. Manure tea is a great way to feed your plants and if sprayed on the leaves will actually fight black spot fungus.

5. 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. You can find 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 you still need to practice prevention methods and always keep an eye out for black spot on your roses.
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[vikki9]

on 8/1/2009 Thank you for this thorough information about roses with black spots.