Crown Gall

Crown gall on rose. Tumor-like growth at the soil line. Photo courtesy of G. Hammond.

Crown gall on rose. Tumor-like growth at the soil line. Photo courtesy of G. Hammond.

We received an email last week from our friend Gaye Hammond a Master Rosarian with the Houston Rose Society regarding a sighting of crown gall on roses. Besides roses, crown gall affects many woody ornamental plants, fruit trees and brambles.

Crown gall is caused by a soil-borne bacterium Agrobacterium tumefaciens. Once in the soil, the crown gall bacterium can survive for several years in decomposing galls from infected plants. The bacterium gets into the plant through wounds that occur during planting, grafting, pruning or by chewing insects feeding beneath the soil.

Infection by Agrobacterium tumefaciens causes the host plant to produce hormones that cause abnormally rapid cell division and enlargement of stem or root tissue. The young gall is light green or white and soft, as it matures, the gall becomes darkened and woody. They vary in size from pea-sized to several inches in diameter. Galls that develop interfere with water and nutrient uptake. As the disease progresses, symptoms will include stunted growth, yellowing foliage and reduced flower production.

Fist-sized gall on crapemyrtle.

Fist-sized gall on crapemyrtle.

Growers:

  • There is no known cure for crown gall.
  • Strict sanitation is necessary to prevent the spread of crown gall especially during ┬ápropagation or grafting.
  • Clean and sanitize all production facilities, knives and clippers.
  • Proper stock plant management will insure a reliable source of clean stock.

    Stems infected by Agrobacterium tumifaciens on crape myrtle.

    Stems infected by Agrobacterium tumifaciens on crape myrtle.

Landscapers:

  • There is no known cure for crown gall.
  • If crown gall is found in the landscape, remove the infected plant and as much of the root system as possible. Do not replant with another susceptible species.
  • Do not purchase nursery stock that has suspicious swellings or galls on the roots or stems.
  • Consider planting other woody ornamentals resistant or immune to crown gall (Table 1)
  • Avoid wounding of any kind especially during planting.
  • Biological control of crown gall by a nonpathogenic strain of Agrobacterium radiobacter is an option. radiobacter competes with A. tumefaciens both as a soil saprophyte and for attachment to wound sites. Some strains also produce a toxin that is active against strains of A. tumefaciens. This agent is available commercially as Galltrol A, Norbac 84C, Nogall or Diegall*.

Table 1. Woody ornamentals resistant or immune to crown gall.

Abelia Ailanthus Albizia Amelanchier Berberis
Betula Buxus Calluna Carpinus Catalpa
Catalpa Cedrus Cercis Cladrastis Cotinus
Cryptomeria Deutzia Fagus Ginkgo Gymnocladus
Ilex Kalmia Koelreuteria Laburnum Larix
Leucothoe Liquidamber Liriodendron Magnolia Mahonia
Nyssa Picea Pieris Pyracantha Rhus
Sambucus Sassafras Tsuga Zelkova

 

Additional Resources:

Lacy, G.H, and Hansen, M.A. Crown Gall of Woody Ornamentals. Viginia Cooperative Extension. https://pubs.ext.vt.edu/450/450-608/450-608.html

Hammond, G. Identifying Crown Gall Disease. The Arborgate. http://arborgate.com/blog/identifying-crown-gall-disease/

*Commercial products named in this blog post are for informational purposes only.

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