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Crown gall

Agrobacterium tumefaciens (Smith and Townsend) Conn

Infected trees are often stunted and produce small, chlorotic leaves. Spherical to elongated swellings (galls) along the roots or on the trunk just above the soil line is the primary symptom (A). Young galls are smooth and soft, and the bark tissue is often pale relative to the surrounding healthy tissue, but galls darken as they age. The galls may completely surround the root or crown or may appear as a growth off to one side (B). Galls start small and can grow to a typical 0.6 to 10 cm in diameter.

Distribution

Widespread; common to all fruit-growing regions in eastern North America.

Similar Species

Any disease or disorder affecting the root system or rootstock/scion union can produce similar above-ground symptoms. The presence of galls distinguishes this disease from similar disorders.

Management

It is necessary to carefully inspect nursery trees for the disease before planting, as serious problems can often be attributed to the introduction of infected nursery material. In the orchard, natural infections can be avoided by minimizing wounds to the trunk along the soil line; natural infections, however, rarely result in serious losses. Infected trees should be removed. However, populations of bacteria do not diminish markedly during the first several months after their removal (and may actually persist for several years); therefore, replanting in the same site with a susceptible host should be avoided.

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