The Q&A Archives: Black Spot On Roses

Question: I have been hand spraying with the Ortho Fungicide and at first it seemed to help, but now all the leaves are getting black and falling off. I water at the base and not on the bushes. Please advise best way to totally eliminate the problem. Is there any other product or just I just rip them all out, treat the soil with something and start anew?

Thanks for any help you can give.

Answer: A fungus causes black spot on roses and some cultural
practices may be helpful in controlling it, but probably not in completely eliminating it. Your options include
planting varieties resistant to it, ensuring your plants are in a location with good air circulation, avoiding wetting the leaves when watering, and cleaning up, removing and destroying any infected leaves. Do this especially well each fall to minimize reinfection from year to year. A clean layer of organic mulch (such as shredded bark or half finished compost or chopped leaves) applied before the plants leaf out again in spring should also help prevent reinfection.

Neem oil may also be helpful. At the current time, the only
neem product I have seen that contains neem oil (rather than
the ingredient azadirachtin) as the active ingredient is Green
Light's Rose Defense. It is available through Gardener's Supply
Co, Burlington, VT. 800-863-1700, Neem controls
aphids and mites on your roses, and the oil version of neem
also will control powdery mildew and black spot.

Some gardeners have had success using baking soda and
water sprays to control black spot. Tests in England
indicated that 1.5 tablespoons of baking soda in 1 quart of
water was effective. Add a few drops of dish detergent to
help it stick. You may want to try it and see for yourself.
Caution: Always test something new like this on a few leaves and wait a few days to see the results before spraying all of your plants.

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