Eric Coombs, Oregon Department of Agriculture, Bugwood.org
Crown gall is the more widespread of the two diseases and affects all brambles as well as apples, grapes, peaches, and roses. Only grass-like plants seem to be immune to crown gall. Cane gall occurs only on brambles, with black and purple raspberries being 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 the death of the plant.
Crown and cane gall are characterized by the spongy, rough, pinhead- to golf ball-sized, tumor-like swellings that become brown, woody knots with age. 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. More intense gall formation seems to occur in years with higher incidence of winter injury. The diseases cause the production of dry, seedy berries and the stunting and prevention of new cane formation. Weakened canes are broken easily by the wind and are more susceptible to winter injury. The plants might show water stress and nutrient deficiency symptoms since the movement of water and nutrients throughout the plant is disrupted. With cane gall, black and purple raspberries are more often infected than red raspberries and blackberries.
Both diseases are caused by soilborne bacteria (crown gall: Agrobacterium tumifaciens and cane gall: Agrobacterium rubi) that infect the plant only through wounds. Wounds can result from natural causes (e.g., insect feeding, frost damage) or from mechanical causes (e.g., pruning, cultivating, harvesting). The bacteria overwinter in the soil and in galls. Bacteria are then spread by splashing rain, running water, cultivation, and pruning from soil and infected plants. As the galls enlarge, the soil can become heavily infested and will remain so for many years.
The best control measure is prevention. Plant only certified, disease-free nursery stock, and take care not to wound the plants, especially the root systems, 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. Dispose of the soil surrounding the roots of the affected plant. Titan seems to be especially susceptible to crown gall, as do some of its relatives. No chemical control is known.