Climbing roses as a group tend to be quite hardy, but some older cultivars often don't have a high degree of disease resistance. The three most common diseases associated with all roses, including climbers, are the fungus diseases powdery mildew, black spot and rust. Less common problems include downy mildew and the virus diseases, rose mosaic, rose spring dwarf disease and ring spot.
Powdery mildew is one of the biggest problems associated with climbing roses, especially ramblers. It develops during periods of warm humid days and cool nights. By the time the "white powder" has appeared, the fungus has spread rapidly. Crowded plantings or damp, shaded locations are also ideal conditions for development.
Downy mildew appears as thick, grey fuzz and is highly destructive, growing deep into plant tissues. It can cause rapid, severe defoliation. It is not as common as powdery mildew and is active only in the cool, damp conditions of spring and fall.
Black spot, while not as big a problem on climbing roses, nevertheless must be contended with. Black spot appears as circular black spots with irregular edges, surrounded by yellow tissue. The disease develops in periods of high humidity or excessive rain and can be spread by splashing water, garden tools, clothing or your hands.
Rust is a fungus that is most prevalent in the western United States and is most prevalent in humid, cool conditions. Leaves develop reddish-orange bumps on the upper leaf surface.
Very little in known about the transmission of plant viruses. The most common mode of transmission seems to be through grafting, but this is not definitive. Rose mosaic, carried by insects, is the most common rose virus. Symptoms are mainly seen on new growth in the spring. Leaves become mottled with yellow patches, streaks or stripes.
Roses infected with the rose spring dwarf virus exhibit short leaves that are curved or clustered into a ball, or clump on short stems.
Ring spot is also caused by a virus. Early in the season the symptoms resemble mosaic, but later infections result in ring spotting on leaves. The disease can be spread by aphids.
There is no treatment or cure for virus diseases, so infected plants should be destroyed. Spray to prevent carrier insects such as aphids, wash your hands and disinfect all tools.
The best course of action when dealing with climbing roses is prevention. The plants can grow quite large and be difficult to treat. Choose cultivars that are known to be resistant in your area. Purchase plants from a reputable nursery. Water early in the day and prevent splashing.
Choose a location with plenty of sunshine and good air circulation. Avoid the tendency to plant climbing roses along a brick wall or near a dense hedge that can cut off air circulation. Keep sufficient space between plants. Provide proper support for the canes, and prune away dead, diseased or spindly growth.
Good sanitary habits can also help prevent the spread of these diseases. Mulch your plants to prevent infected material from coming into contact with the soil, and do not compost mulch that has been in contact with infected material. Remove infected leaves, blossoms or stems immediately and discard in the trash. Disinfect all garden tools before handling healthy plants.
If a fungus disease is detected, treat with a fungicide. This may be difficult in the case of climbers and may require the use of a ladder. It is important that spraying is done thoroughly. Both the top and bottom leaf surfaces need to be treated. If the affected area is out of reach, you may have no choice but to cut and remove the infected material. In periods of high humidity, institute a spraying program with a fungicide. This will prevent spores from rooting and becoming established.