Crown Gall

Crown gall is a bacterial disease caused by Agrobacterium tumefaciens that infects more than 2,000 species of plants. Crown gall of grape is a major problem in cold climate regions. Wounds are necessary for infection to occur. Observations suggest that freeze injury wounds are highly conducive to infection. The disease is particularly severe following winters that result in freeze injury on cold-sensitive cultivars, such as those of Vitis vinifera. Crown gall is characterized by galls or overgrowths that usually form at the base of the trunk. Galls form as high as 3 feet or more up the trunk (aerial galls). Galls generally do not form on roots. The disease affects all grape cultivars. Vines with galls at their crowns or on their major roots grow poorly and have reduced yields. Severe economic losses result in vineyards where a high percentage of vines become galled within a few years of planting.

Symptoms

The disease first appears as small overgrowth or galls on the trunk, particularly near the soil line. Early in their development, the galls are more or less spherical, white or flesh-colored, and soft. Because they originate in a wound, the galls at first cannot be distinguished from callus. However, they usually develop more rapidly than callus tissue. As galls age, they become dark brown, knotty, and rough (Figure 81).

Figure 81: Crown gall symptoms on grape trunk.

When galls are numerous on the lower trunks or major roots, they disrupt the translocation of water and nutrients, which leads to poor growth, gradual dieback, and sometimes death of the vine. In some cases, infected vines appear stunted and as if they are suffering from nutrient deficiency.

Life Cycle

The causal organism, a bacterium, is soilborne and persists for long periods in plant debris in the soil. Fresh wounds are required to infect and initiate gall formation. Wounds that commonly serve as infection sites are those made during pruning, machinery operations, freezing injury, or any other practice that injures the vine. In addition to the primary galls, secondary galls may also form around other wounds and on other portions of the plant, even in the absence of the bacterium. Crown gall bacteria also survive systemically within grapevines and probably are most commonly introduced into the vineyard on or in planting material.

Control of Crown Gall

Examine new plants before planting, and discard any that have galls. Wounding by freeze injury appears to be important in the development of crown gall. If winter injury is controlled, crown gall may not be an important problem. Prevent winter injury to vines. Practices, such as hilling or burying vines of cold-sensitive cultivars is beneficial. Proper pruning practices and proper crop loads for maximum vine vigor will result in stronger plants that are less susceptible to winter injury. Controlling other diseases, such as downy and powdery mildew, is also important in preventing winter injury and crown gall.

The double-trunk system of training, in which each trunk is pruned to carry half the number of buds, may help reduce crop loss caused by crown gall. If a diseased trunk must be removed, the remaining trunk can be pruned, leaving the full number of buds until a second trunk is established. Galls on arms or the upper parts of the trunk can be removed by pruning.

There are no current chemical or biological control recommendations for crown gall on grapes.