Disease

Crown gall

Agrobacterium tumefaciens

A soil bacterium that enters through wounds near the soil line and makes the plant grow rough, woody tumors. It is common on rose, euonymus, willow, poplar and fruit trees; young plants can be stunted or killed, while old trees often live with it for years.

Signs

• Rough, tumor-like lumps at the soil line, on the roots or on lower stems.
• Galls start small, light and soft, then turn dark, woody and cracked.
• Slow growth, small leaves and dieback on badly galled plants.

What favors it

Wounds at the soil line from planting, cultivating, mowers, grafting and insects, in soil where infected plants grew before.

Prevention

• Buy plants with no lumps on the roots or at the soil line.
• Avoid wounding roots and the base of the stem when planting and weeding.
• Where it has been a problem, plant grass there for 3 years, or resistant trees such as beech, ginkgo, holly, magnolia or conifers; the bacteria live in the soil.

Crops it shows up on

Apple, pear & stone fruit; Roses & ornamentals; Shade & ornamental trees.

Often confused with

Sources

• Crown gallUniversity of Minnesota Extension
• Crown GallUniversity of Wisconsin-Madison Extension
• Crown GallMontana State University Extension
• Crown GallUMass Amherst Extension

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