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Roses are some of the most popular and beautiful flowers in flower gardens all over the world. They offer iconic flowers and heavenly aromas that other plants just don’t. But, if you are a gardener who attempts to grow these magnificent plants, you will find that they require a great deal of attention in terms of their health and care. Roses are very susceptible to disease regardless if you are an experienced gardener or a beginner. And, not just one or two diseases…many different ones, so learning how to protect your roses from disease is crucial information. Maybe only tomatoes rival the number of diseases roses can contract!
Different types of roses vary in their resistance to diseases and the maintenance they require. To be successful in growing roses, you should select varieties that require an amount of care equal to that which you are able to provide. Generally, shrub roses bloom well with few chemical controls needed, while other varieties more susceptible to disease, like hybrid tea roses, require an effective spray program before the growing season begins.
In this article, we’ll look at five of the most common rose diseases and what you can do to both treat them and protect your roses against them. At Get Right Enterprises, we have expert landscape artists and designers who can help you get the just the right flower garden for your yard, in addition to keeping your rose plants healthy all year long.
Common Rose Diseases
These are some of the most common rose diseases in North Carolina:
Black spot is one of the most common and serious rose diseases you will encounter. It is caused by the fungus Diplocarpon rosae and will defoliate and weaken your plants to other environmental pressures. Black spot is unlikely to kill your roses by itself, but it weakens the plant to other infections. It is most severe in the spring and fall when conditions are wet and nights are cool. This prevents moisture from evaporating. Symptoms are circular, black spots on the rose leaves surrounded by a yellow area. The infected leaves often drop from the plant and the infection can last all summer. If the roses contract black spot in the spring, by the middle of the summer, severely infected plants can lose all of their leaves. Additionally, the fungus can survive during the winter in infected leaves and canes, so your roses can be infected year after year.
How to Treat
Black spot can be treated with a few different types of sprays, but it is a very difficult disease to handle once an infection sets in, so early care is critical. Sulfur-based fungicidal sprays can be effective. Spray a mixture of a teaspoon of baking soda with a quart of warm water as another option to protect roses from disease.
You can greatly reduce the spread of black spot and minimize future infections by following these practices:
- Plant resistant varieties
- Maintain good sanitation
- Remove and destroy infected canes
- Keep leaves dry
Powdery mildew is caused by the fungus Sphaerotheca pannosa rosae and produces a grayish white powdery substance on the surfaces of young leaves, shoots, and buds. Flower buds may fail to open and some leaf drop may occur. Buds that do open may have poor flowers. Powdery mildew can occur almost anytime during the growing season when temperatures are mild (70 to 80 degrees Fahrenheit), and when the relative humidity is high at night and low during the day. It is most severe in late summer and early fall, and in shady areas.
How to Treat
Spray all parts of the plant, including the tops and bottoms of leaves, with a fungicide. Do this on a regular schedule.
A thorough fall cleanup of all shed leaves helps to minimize recurrences. Rake up and destroy leaves under the plant in the fall. Planting resistant varieties is the best defense.
Rose flowers and buds are often infected with the gray-brown fuzzy growth of the gray mold fungus Botrytis cinerea. The fungus is most active when temperatures are 62 to 72 degrees Fahrenheit and conditions are moist. This is an ugly disease that causes flower petals to have small, light-colored spots surrounded by reddish halos. Buds fail to open and often droop. It most often attacks tea roses. A hot and humid summer is a breeding ground for this disease.
How to Treat
If chemical control is necessary, fungicides containing thiophanate methyl, chlorothalonil or neem oil can be used.
To prevent this blight, keep the area clean by collecting and discarding all the fading flower blossoms and leaves. Provide good air circulation and avoid wetting the leaves when watering. Disease can develop on canes that have been damaged, on canes that are kept too wet by the use of manure mulch, or on wet leaves.
Rose rust is caused by the fungi Phragmidium species. It causes orange-colored spots to appear on stems and leaves. In severe cases, an orange dust-like substance can be present on the plant surface and on the ground below the plant. Rose rust can be on all parts of the plant except for the roots and petals. It turns leaves yellow or brown and causes them to drop.
How to Treat
Remove and destroy diseased leaves and plants. Fungicides containing myclobutanil, mancozeb or propiconazole are recommended.
Provide good air circulation. Do not plant roses in crowded areas and prune plants to keep the centers open. Water plants before noon and avoid getting the leaves wet. Remove and destroy diseased leaves and plants.
Rose rosette disease is an untreatable disease caused by the Rose rosette virus (RRV). This virus is introduced into the rose during feeding by the rose leaf curl mite (Phyllocoptes fructiplilus). This mite feeds on cell sap from the tender stems and leaf petioles. The rose leaf curl mite causes little damage while feeding but, if it is a carrier of RRV, symptoms will appear in one to three months. Once a rose has symptoms, it may have already spread to adjacent plants. Infected plants typically die within a couple of years. The symptoms are bizarre vibrant red growth on the plant, deformed and brittle leaves with yellow and red pigmentation, and an increase in the number of thorns on the stems. Wild roses are more susceptible to the rosette virus.
How to Treat
Any wild multiflora roses nearby should be removed and promptly disposed of. Any infected cultivated roses should be immediately removed, then burned or bagged and disposed of with garbage. Remove any roots that might re-sprout later. Do not leave an uprooted infected plant in the garden because the mites may leave that plant and get on other plants nearby. To reduce the spread of the mites, nearby roses can be treated with a bifenthrin spray every two weeks between April and September.
Always space rose plants so they do not touch. Prune your roses hard each year in early spring, cutting back as much as 70% of last year’s growth. This helps remove overwintering mites and potentially infected tissue. Pruners used on diseased plants must be disinfested with rubbing alcohol or a dilute bleach solution before being used on uninfected plants because the sap on the pruners is contaminated with the virus.
Call Us for Help!
Call us at Get Right Enterprises LLC for more information on how to protect roses from diseases. We specialize in assisting you in planting the flowers that flourish best in your environment. Call us at 910-264-6782 or fill out our form below.