Diseases that affect climbing roses are for the most part the same as those that affect bush roses. Leaves, flowers, stems and seeds all can be damaged by disease, and in the worst cases, death of the rose occurs. The good news is that today’s climbing roses are much more disease resistant than in generations past, and are, in fact, less often affected than shrubs.
There are three main types of rose disease: fungal, viral and bacterial. Common fungal diseases include black spot, rust and powdery mildew; rose mosaic is the most common viral rose disease, while the most common bacterial rose disease is crown gall. Each type must be treated differently; while fungal infections are the most common, bacterial and viral infections often have the more serious consequence of requiring the pulling out of the plants.
Many plant diseases are limited by geography or climate. Choose your climbing roses with an eye to your location and consult a garden center if you’re unsure. Plants that are billed as disease-resistant in some areas could be disease-prone in others. For instance, fungal diseases are more common in humid, warm climates than in northern, dry areas. Fungal infections in all types of plants are more common in USDA cold hardiness Zones 5 to 8. Powdery mildew in particular requires extended warm, wet periods to arise. The rose mosaic virus is widespread across the United States and Europe.
To treat a climbing rose disease, you must first identify it. Black spot fungus can be seen as round black spots on leaves, which is followed by yellowing leaves. Stems also swell and redden before blackening into lesions. A similar fungus is called anthracnose, which produces dark spots on leaves, progressing to holes in the leaves.
Rust infection shows as rust-colored spots on the underside of rose leaves. In powdery mildew, white or gray patches of fuzzy mildew show up on leaves, buds and twigs. A less common but more damaging fungus is downy mildew, which creates dark purple spots edged with yellow.
The rose mosaic virus causes yellow lines, rings and irregular spots on leaves and stunts plant growth. The bacteria that causes crown gall enters through plant wounds and produces a woody growth or gall on the stem or root.
Fungal infections require warm, wet conditions to incubate. Good air circulation through your climbing roses will help prevent fungus; prune or thin plants so they are not crowded and plant them in a full sun location so they dry after rain.
When watering, avoid getting leaves wet and don’t overfertilize your roses. Plant in well-drained soil.
To prevent crown gall, avoid injuring the roses while planting or digging, especially at the crown or roots. Rose mosaic virus is only spread through cutting and grafting, so you must take care to choose rose stock from nurseries that are virus free.
You also can select roses that are more disease resistant; one such climbing rose is “William Baffin.”
Many diseases can be treated with fungicides or bactericides. Home remedies such as mild detergent, vinegar spray or pepper spray can sometimes be effective. To help with black spot or rust, spray plants with a combination of lime sulfur and dormant oil in the spring. To kill powdery mildew, spray with potassium bicarbonate.
Viral diseases are usually not curable and must be controlled instead. Removing plants with viruses from your garden is the best way to prevent the disease from spreading. That includes roses with rose mosaic, its cousin tobacco mosaic and the rare but virulent rose rosette virus. Bacteria-infected plants might also need to be culled, but some infections can be eradicated through treatment.