Chapter 20

Managing Vineyard Diseases

Bacterial Pathogens

Grape Crown Gall

Crown gall, caused by the soil-borne bacterium Agrobacterium vitis, seldom causes disease unless the vine trunk is injured. A. vitis survives for long periods of time in soil, in galls and in diseased plants. Grapevines grown in areas subject to freezing winter temperatures are especially vulnerable to crown gall because freeze injuries provide a wound where the disease can initiate.

Symptoms

Infection occurs as a result of wounds or injury. A. vitis is characterized by rough galls or overgrowths on the roots, trunk, and arms of grapevines. Despite the more frequent occurrence of the bacterium in the root system, the galling can be more destructive near the base of the trunk. In young vines, the galls can girdle the trunk, killing the vine. In older vines, heavy galling can disrupt the vine’s ability to internally transport water and nutrients leading to poor growth, gradual dieback, and sometimes death of the vine.

Transmission

The causal organism is soil borne and persists for long periods in plant debris. Fresh wounds are required to infect and initiate gall formation. The bacterium is systemically present in the majority of grapevines, but seldom causes disease unless the vine is injured.

Disease Management

Cultural Practices: Prevention is the best means of controlling crown gall. This can be accomplished in a number of ways such as avoiding poorly drained, low-lying areas, because the disease tends to be much more severe in such locations.

Chemicals: To date, no effective chemical treatments are available for grape crown gall control. Topical treatments of antibiotics or other bactericides may kill bacteria on the surfaces of galls, but fail to control the pathogen residing systemically.

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