Crown and cane gall are bacterial diseases that seriously limit raspberry production in Pennsylvania. Crown gall is the more widespread of the two diseases and affects all brambles including apples, grapes, peaches, and roses. Only grasslike plants seem to be immune to crown gall. Cane gall occurs only on brambles. Black and purple raspberries are more frequently infected than red raspberries and blackberries. The impact of the disease on plant growth and production can range from no apparent effect to death of the plant.

Symptoms

Crown and cane gall are characterized by the spongy, rough, tumorlike swellings that become brown, woody knots with age and range in size from that of a pinhead to a golf ball. Crown galls develop in the spring on the underground parts--the roots and crown--of the plants. Cane galls develop as whitish eruptions on the fruiting canes in mid June. These eruptions later turn brown and then black, and begin to disintegrate. The diseases cause the production of dry, seedy berries and the stunting and prevention of new cane formation. Weakened canes are easily broken by the wind and are more susceptible to winter injury. The plants may show water stress and nutrient deficiency symptoms since the movement of water and nutrients throughout the plant is disrupted.

Disease Cycle

Both diseases are caused by the soil-borne bacteria Agrobacterium tumefaciens (crown gall) and Agrobacterium rubi (cane gall), which infect the plant only through wounds. Wounds can result from natural causes or from mechanical causes (pruning, cultivation, harvesting, insect feeding, frost damage). The bacteria overwinter in the soil and galls and are spread by splashing rain, running water, cultivation, and pruning from soil and infected plants. With growth of the galls, the soil can become heavily infested and will remain so for many years.

Disease Management

The best control measure is that of prevention. Plant only certified, disease-free nursery stock, and take care not to wound the plants, especially the root system, at planting time. Try to plant only in sites with no history of the diseases, or wait at least 3 to -5 years before replanting in the site. If a diseased plant is detected, remove and burn the roots and tops of the plant. No chemical control is known.

Management practices that minimize the risk of cold injury are currently the only practical technique for managing the disease. Here in the Northeast, cold injury is by far the most important factor. These techniques include careful site selection for cold-sensitive cultivars and cultural practices that promote winter hardiness. Hilling above the union of grafted vines protects buds from freezing and ensures the development of new scion shoots that may be needed for trunk renewal. The use of multiple trunk vines and yearly replacement of dead trunks with renewals helps to manage the disease at a tolerable level. In some areas growers bury young vines in the fall to reduce freeze injury.