Anthracnose, commonly called "cane spot" or "gray bark," occurs in several species of Rubus. It is considered an extremely serious disease of black, purple and susceptible cultivars of red raspberry. Severe yield loss may result due to defoliation, wilting of lateral shoots, death of fruiting canes, and reduction in fruit size and quality.

Symptoms

Anthracnose symptoms are most conspicuous on canes but can also occur on leaves, petioles, flower buds, and fruit. In the spring, reddish-purple spots appear on young canes. As the disease progresses, the spots enlarge and the centers become sunken. These early lesions on the cane are called pit lesions. By late summer or early fall, the typical "gray bark" symptom can be observed, especially on the red raspberry. Within these lesions spores are produced, which are spread by running water, splashing rain, and wind. Canes weakened by anthracnose are more susceptible to winter injury and eventually may die. Cankered canes may also produce abnormal fruiting branches with malformed fruit, especially in seasons of drought. Fruit infections are not common unless there is a high level of anthracnose in the plantings. Infected fruit is typically dry and seedy.

Disease Cycle

Anthracnose is caused by the fungus Elsinoe veneta, which overwinters on canes infected the previous season. In the spring, fungal spores are produced on these diseased canes. These spores are spread to very young green tissue and infection takes place. The primary damage to plants is caused by these early infections.

Disease Management

Control can be achieved by sanitation and spraying. Although sanitation is labor intensive, it is an effective management practice for the control of anthracnose. The fungus can survive on dead canes that have been pruned off. If pruned canes are left in or near the planting, the disease can spread back into the planting. Removing the pruned canes reduces the potential for disease development.

It is important to plant clean, disease-free nursery stock. Cut out all diseased canes, cane "handles," and any infections observed on new plants. Good air movement through the planting should be provided by the removal of weeds and spindly canes. If possible, all noncultivated brambles within the vicinity should be rogued, for these wild plants will also harbor the pathogen.