Frances Smithson has written an informative article about crown gall disease in the April 1998 issue of The Potomac Rose, Newsletter of The Potomac Rose Society. In this article she tells about a local rose garden that lost more than 60 Peace rosebushes to this disease, how they diagnosed the problem and what they did to correct it. Smithson writes:
While many of the diseases common to roses are caused by fungi, crown gall is the result of soil-borne bacteria. The bacteria enter the plant through an injury or wound that creates an opening into the plant near the ground. In addition to appearing at the crown of the plant and on the roots, the growths may also appear on canes above the ground...
A rosebush infected with crown gall may not show symptoms initially. Because the galls often develop either below the ground or at ground level, they may not be observed until either the plant is declining of the gall grows large enough to be seen when being pruned or a gall is formed on a cane. Infected plants may appear stunted with smaller foliage and blooms and generally seem less healthy than in the past. This is caused by the gall cells growing and damaging the tissues of the plant, reducing the amount of water that can be transported through the plant...
There is no spray avilable to cure crown gall...
The general recommendation is that unless the rosarian has a strong emotional tie to the infected plant, it should be dug up and destroyed.
Agrobacterium radiobacter, strain 84, has proved to be a successful biological control of crown gall when used as a soil drench or when a plant's roots are dipped in it prior to planting. (This product is available through the Helena Chemical Co., Fresno, CA, Tel: 209-453-9385, under the brand name Galltrol-A.)
Summarized from Crown Gall, by A.P. Hert and J. B. Jones, University of Florida, Gainesville, Florida USA in Encyclopedia of Rose Science:
Crown gall is caused by bacteria called Agrobacterium tumefaciens, commonly found on apples, roses, raspberries, peaches and grapes. The bacteria are soilborne and can live in the soil or plant debris for 3 to 5 years years. Roses should not be planted in soil with a history of infection for 3 to 5 years. Soil can be steamed for an hour with water at 130 degrees F or replaced.
There are no chemical pesticides to control Agrobacterium tumefaciens, but biological control does provide some protection. Before planting, roots and crown can be dipped in a solution containing genetically modified related bacteria, Agrobacterium radiobacter, strain 84, that protect against infection.
Aerial galls on canes above the ground are rare. Cuttings from healthy-appearing parts of plants should not be used because Agrobacterium tumefaciens has been shown to move systemically into healthy parts of the plant.
