Hardiness Zone: 7a
Ann from MA
I agree with Elaine (in the feedback forum below). It sounds like your roses have experienced a fungal disease called Black Spot. Black Spot is a serious, but controllable, disease commonly seen in floribundas, hybrid teas, and grandifloras. For whatever reason, shrub roses don't seem to be affected by it as much.
Black Spot is caused by fungal spores and typically occurs during warm, moist conditions when rainwater splashes the spores up onto the foliage from the ground. Black spots and yellow patches appear on the leaves, which then shrivel up and fall off. If left untreated, a rose bush can quickly lose all of its leaves.
To treat roses with Black Spot, remove any visibly infected leaves and throw them into the garbage. Composting is not recommended, as fungal spores can remain dormant for long periods. Fallen leaves lying under the plant should also be cleaned up and disposed of in the same way. To prevent Black Spot from spreading to more leaves, dissolve 1 teaspoon of baking soda in 1 quart of water and spray the infected plants thoroughly. Severe infections can also be controlled with sulfur, which is readily available at garden centers.
You can't control the rain, but you can help control the spread of Black Spot by mulching around your roses to help prevent water from splashing the plants. Water your roses as early as possible in the day so leaves have time to dry, or avoid wetting the foliage altogether by watering from below.
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Ann, do they also have black spots on the yellow leaves? If they do, you have blackspot. There are several remedies. First of all, pick off all the yellow leaves and discard but not in a compost pile. They are diseased and you do not want them in there. Any that fall on the ground, pick them up and dispose of them. Then mix 1/2 skim milk and 1/2 water and spray them really good. You should do this about every three weeks as a preventive measure.
Also, I use cornmeal around mine. Just sprinkle it on ground and water it in. Maybe 1/2 cup per bush. Why this works I do not know, but it does. Good luck. Get at it right away so you do not lose all your leaves. It will not kill your plant by the way, just makes it look bad. (07/02/2008)
Another reason leaves can suddenly turn yellow is a lack of magnesium. Diluting some Epson Salts in water and spraying over them will help. (01/21/2009)
By Cathy from Townsville, QLD
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