The beauty of roses doesn’t come without a cost; rose plants are susceptible to numerous diseases. To enjoy beautiful roses in your garden you must be able to recognize the diseases and know what to do to prevent and treat them.
Common Diseases of Roses and Their Control
Following are a few of the more common rose diseases and what you can do about them:
Powdery mildew is a common fungal disease of roses. It is particularly problematic in dry climates, but affects roses in humid locations as well. Some types of roses are more susceptible than others; gardeners should choose the most resistant varieties for their locations. Powdery mildew causes leaves to become distorted and covered with a powdery coating.
Sanitation is the first step to controlling powdery mildew—you must routinely remove old and dead leaves. Prune stems when the plants are dormant. Since powdery mildew flocks to lush new growth, limiting fertilizing in early spring may help. To control powdery mildew you may need to apply fungicidal sprays when new growth appears in the spring.
Blackspot is another common and serious disease of roses. Black sooty spots start with feathery edges and develop yellow margin as the disease develops, causing defoliation by late in the season. Dormant pruning and sanitation reduce the spores that overwinter in the garden. Prune plants and space them generously to ensure good air circulation. Avoid overhead watering.
Downy mildew thrives in humidity. While garden sanitation can reduce spores, fungicides may be needed in damp conditions. Although no roses are entirely resistant to downy mildew, it helps to plant resistant types, especially if you garden in a humid climate.
Anthracnose is most serious in cool and damp spring conditions. At first the black spots on the leaves look quite a bit like blackspot. While roses, climbers, and ramblers are most susceptible, hybrid teas and bush roses are not immune. Remove old leaves from the base of the plant and prune out diseased canes. Springtime application of fungicides can help control the disease.
Botrytis causes young flower buds to droop and turn black at the base. Fungal spores enter roses through wounds or pruning cuts and are spread by air currents and blowing rain. Meticulous garden sanitation is the best way to prevent botrytis. Remove infected plant parts, provide good ventilation, and wait for the weather to turn dryer.
Canker-causing fungi cause stems to yellow and develop yellow spots that turn brown or black. The canker fungus is most active when rose plants are inactive, entering through pruning cuts or stem wounds. Remove dead canes and promote vigorous growth to keep canker diseases at bay. Pruning cuts, especially in winter, should be at an angle and close to an active bud. A dormant oil spray can prevent pathogens from entering canes. The risk of canker disease is much less when the plants are actively growing.
Rose rust is most likely to appear when the air is cool and moist during the rose plant’s active growing season. Leaves, flowers, and growing canes as all susceptible. Sanitation reduces spores and infestations. Dense rose bushes benefit from pruning to reduce moisture in the middle of the plants. Preventive fungicidal sprays may be needed.
Tips for Controlling Rose Diseases
Like people, healthy plants are more resistant to diseases. Give your roses everything they need to thrive and they will reward you with beautiful blooms on strong plants. Here’s how you can have a successful rose garden and minimize the use of chemical pesticides:
- Choose roses that are suited to your climate and your specific location and that are resistant to the roses diseases that are common in your area.
- Sanitation is key. Remove dead and diseased plant parts from the garden.
- Plant your roses in full sun in soil high in organic matter. Roses need some shade in very hot climates.
- Allow plenty of space between the plants and prune inner canes to ensure good air circulation around and inside the plants.
- Occasional deep watering is better than frequent shallow watering. Water the roots, not the foliage.
- Mulch with organic matter to control weeds, keep roots cool, and maintain even moisture.
- Inspect plants regularly to catch problems early.
Want to Learn More About Rose Diseases?
The more you know about roses the better able you will be to prevent and control problems. Many beautiful and informative books have been written about roses. Your cooperative extension service can tell you the best roses and gardening methods for your region. Plus, you can learn about growing roses from these websites: