Crown gall—Agrobacterium tumefaciens
Crown gall hosts include chrysanthemum, dahlia, geranium,
marigold, peony, and snapdragon. The crown gall bacterium
causes distorted growths or galls, principally on the basal
stem and root crown at the soil line or just below the soil
surface. Galls
sometimes also form on roots, limbs, and trunks of many species
of woody plants. Under moist conditions, galls may
appear on upper stems or even leaves of some plants. Infected
plants may become distorted, grow slowly, and become stressed
and susceptible to drought or other problems. Foliage
may be chlorotic and leaves may be small.
Solutions
Sanitation is the most important management
strategy for crown gall. Clean tools, containers, and
work surfaces frequently and treat them with a commercial
disinfectant. Use only high-quality plants. Avoid
injuring plants, especially around the soil level and when
plants are wet. Dig out and destroy infected plants. In
hot areas, solarizing the
soil before planting can reduce crown gall bacteria in the
soil. Infection may be prevented by dipping cuttings
in Agrobacterium tumefaciens K-84, a biological
control agent that produces an antibiotic that reduces or
eliminates infection.
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Distorted trunk growth on a dying Euonymus plant infected with crown gall
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