Latin name: Agrobacterium tumefaciens and A. rubi
Reason for Concern:
1) Serious threat to susceptible blackberry variety production.
2) Root infections may go undetected until galls are so numerous that plant vigor is affected.
3) With infected plant stock, yield can be significantly reduced, but susceptibility varies by variety.
4) Infected plants show stunting as galls interfere with water and nutrient flow.
Spongy, rough, tumor-like swellings that age into brown, woody knots ranging from pinhead to tennis ball size. Crown Galls develop in spring on roots and plant crowns and as whitish eruptions on fruiting canes in spring/summer. Eruptions later turn brown to black. Some disintegrate over time, while others remain for the life of the plant. Galls can cause canes to split open, or cause the production of dry/seedy berries, stunting and can prevent the growth of new canes. Plants may show water stress and nutrient deficiency symptoms because nutrient movement throughout the plant is disrupted. If infection is not severe, tops of infected plants may appear normal. Symptoms may not develop for over a year if infection occurs when temperatures are below 59F. If the fruiting canes produce short, weak laterals, leaves turn yellow and dry at the edges and curl up at the onset of warm weather. Root systems from these dying plants can resemble a string of beads (galls).
Crown and cane gall are caused by soil-borne bacteria that infect the plant through wounds only, which can result from lateral root formation, leaf scars and winter injury or from mechanical causes (pruning, cultivation, harvesting, insect feeding). The bacteria overwinter in the soil and galls are spread by splashing rain, running water, cultivation, and pruning from soil and infected plants. Heavily infested soil will remain infested for many years. Inoculum remains in the ground for a very long time after infected plants are removed and the bacteria survive almost indefinitely in decaying root galls or in alternate hosts.