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Crown gall (Agrobacterium tumefaciens and Agrobacterium rubi) is a bacterial disease that affects a wide range of plant hosts, including brambles. Galls girdle canes, causing stunting, low vigor, poor fruit set, and cane dieback. Severe infections lead to plant death. Lumpy round galls develop in late spring and expand throughout the season, turning brown to black. Galls are formed as bacteria enter canes and roots through wounds (pruning cuts, insect punctures, freeze damage). Most severe symptoms occur on plants that are infected when young. 

Crown gall on crown of blackberry.

(Photo: Chris Smigell, University of Kentucky)

Management: 

• Begin with disease-free stock plants.
• Avoid wounding.
• Rotate crops if site has a history of disease.
• Consider planting resistant or tolerant cultivars.

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