Cane Blight Of Caneberries and Roses

Cane blight is a disease of caneberries and roses caused by a fungus that has been given multiple Latin names as above. The fungus can girdle and kill stems.

Identification

Infection generally occurs in new canes during the spring, but symptoms do not become externally obvious until fall or the next growing season. The infected areas develop a black, brown, dark red, or purple sunken area (canker) that is commonly elliptical. Cankered bark may crack open or the cane may break. Severely cankered canes become girdled (killed all around their circumference), causing the shoot to die outward or upward from the canker.

Branches infected and killed by cane blight wilt and turn black or brown. Dead leaves cling to the dead canes.

Dead or dying canes develop black to gray specks, which are the asexual fruiting bodies (pycnidia) of the fungus. During wet conditions pycnidia develop an ooze of gray spore masses. During dry conditions the spores can appear fuzzy, powdery, and whitish.

Scraping the bark of an affected cane exposes vascular tissue. Healthy tissue should be moist and pale green or white. Diseased tissue is orangish to reddish brown. Vascular discoloration generally extends above and below the site of the external wound.

Life cycle

The fungus overwinters on diseased canes. During moist weather, spores are produced and dispersed in splashing irrigation water or rain and by moist wind. The pathogen readily infects wounded or weakened areas of canes. Stem cankers commonly develop at the cut end of canes when stubs are left by poor pruning practices. It can also infect canes through tissue damaged by abrasions, cold weather, insect feeding, or thorn scars.

Damage

When a wound becomes infected, generally in spring, the pathogen spreads internally in the vascular system. Outwardly noticeable disease symptoms do not appear quickly. By late summer or fall, well after the initial infection, discolored lesions can appear near wounded sites. In the spring after the initial infection, buds may fail to open. If the cane develops large cankers, it wilts and dies outward and upward from the canker, reducing blossom and fruit production.

Solutions

Protect plants from injury because wounds are the site of fungal infection. Provide plants a good growing environment and appropriate cultural care so they grow vigorously.

Prune out infected canes during dry weather during the dormant season. Dispose of prunings away from hosts because they can be a source of infectious spores. Use sharp pruning tools. Make pruning cuts immediately above a node (area with bud formation) and at an angle to leave a minimum amount of dead wood (no stubs).

Where cane blight has been a significant problem and the cultural practices above have been followed, a preventive fungicide can be applied. Bordeaux mixture or another copper fungicide can be sprayed to thoroughly cover the plant during the delayed dormant season, when buds swell in the late winter or spring but before they open. This may reduce cane death the next growing season, but canes can still die during the current growing season because they became infected the previous year.

Adapted from Cane Blight Leptosphaeria coniothyrium, CAB International; Leptosphaeria coniothyrium, Wikipedia; and Raspberry (Rubus spp.)-Cane Blight, Pacific Northwest Plant Disease Management Handbook.