Have you ever noticed that the leaves of rose plants often have black or brown spots (see pictures below)? Around the dark spots, the leaves may also be yellow or very slightly green. This condition is called star sooty mold (also called black spot disease) or in scientific terminology, Diplocarpon rosae. Any gardener who has grown roses has seen black spot disease up close – too close and too often, as most roses are affected by this disease. You can fight it first with homemade black spot disease sprays before resorting to a chemical fungicide or extreme pruning. Discover helpful tips and good home remedies for black spot below!
Table of Contents
- Roses get yellow leaves and brown spots: symptoms.
- What causes rose black leaf spot?
- Yellow leaves and brown spots – prevent the development of black leaf spot.
- Treat the black leaf spot with natural remedies
Roses get yellow leaves and brown spots: symptoms
As the name suggests, the first signs of black spot disease are irregularly shaped spots up to 1.5 cm in diameter, especially on the top of the leaves. As the disease worsens, the leaves begin to yellow and eventually fall off the plant prematurely, primarily from the bottom up. Over time, the entire plant may become defoliated and canes may also become infected.
What causes black rot on roses?
The main cause of black spot disease on roses is a fungal infection: it is the most serious disease for rose bushes. The fungus, Diplocarpon rosae, weakens the vitality of the plant by attacking the leaves and gradually killing the plant.
Star sooty mold occurs mainly in early spring and in very few cases in winter. By midsummer, many roses are already defoliated from it. Like most fungal diseases, black spot is favored by a moist, wet environment and cool temperatures – conditions most likely to occur early in the growing season. If not controlled, this disease can interfere with flower formation . Star sooty mold does not usually kill plants in the first year or two, but if it continues unchecked, your roses will become more susceptible to other diseases and may not survive harsh winters. You may find that stardust produces spores that are carried by the wind to other leaves or plants, so other rose bushes will be affected as the spores spread.
Yellow leaves and brown spots – prevent star sooty mold.
Perhaps the most common phrase you hear when talking to a botanist about plant health is, “Prevention is better than cure.”
Take advantage of sunlight: choosing a location with maximum sunlight per day (we’re talking about about 6 – 8 hours) will improve rose hardiness and vigor. Since brown spots and yellow leaves are caused by moisture, constant sunlight and heat will prevent the formation of vapors, eliminating the risk of infection or other fungal diseases.
Water adequately: When watering, be careful not to get the top of the leaves wet, as moisture could accumulate there and never evaporate. Rose plants do not require much watering, so a small watering near the ground is more than sufficient.
Treat star sooty mold with natural means
If you have noticed the symptoms of black spot disease, there are some treatment options you can use to save your roses.
Remove the infestation
Pruning back the yellow leaves on the canes will reduce the risk of spreading the disease. If you notice diseased shoots before the leaves appear, remove them from your rose plant immediately. Try not to throw the infected leaves and stems into the compost. Even a slight breeze could blow the fungal spores back into your rose bushes.
Cure with baking soda and vinegar
Baking soda (baking powder) is a popular home remedy for treating star sooty mold. The typical mixture is 1 heaping tablespoon of baking soda to 1 quart of water. Most gardeners recommend adding a little liquid soap to help the mixture adhere to the plant.
Alternatively, you can make a mixture at home of 1 tablespoon of white vinegar, 1 tablespoon of baking soda and 1 tablespoon of liquid soap mixed with 4 gallons of water.
Neem oil against brown spots
Neem oil is an organic pesticide and is cold pressed from the seeds of the neem tree. The organic oil penetrates the rose plant’s system and protects it from the inside out. Just be careful not to spray the oil on the leaves in the hot sun, as it will burn the foliage.
Fighting star sooty mold with milk
Milk has been shown to be effective against fungal diseases in some cases, especially star sooty mold. Mix 1 part milk and 2 parts water in a spray bottle – and go. Wet both the top and bottom of the leaves, and remove any diseased leaves or other debris from under the rose. Apply the remedy once a week or every two weeks.
Ideally, you should apply the remedy before you notice yellow leaves and brown spots. This method is more of a prevention strategy to help prevent the spread of star sooty mold.