Crown gall—only one chance in 15 years to control this disease

Written by   Russell Fox

One chance in 15 years because it's only at planting that crown gall can be controlled.

What is a crown gall?
Crown gall is the most widely distributed bacterial disease of plants in the world, affecting over 100 species of fruit crops including apple, pear, stone fruits and grapes; and woody and herbaceous ornamentals including rose, poplar and willow.
What does crown gall look like?
Crown gall gets its name from the round or irregularly shaped tumour-like growths (the galls) that usually form on plant crowns just above or below the soil line.
Galls can also form on roots, stems, trunks or branches. Galls can be pea-sized, or as large as 100 mm or more in diameter.
Galls interfere with water transport within the plant. Affected plants will suffer from water and nutrient deficiencies and become stunted. Flower and fruit production is reduced.
Where does crown gall come from?
Crown gall is caused by the bacteria Agrobacterium tumefaciens. The bacterium is spread through movement of contaminated soil, water and infected plant material.
The bacterium enters plants through wounds (e.g. mechanical injury, pruning cuts or nematode feeding sites) or natural plant openings (e.g. lenticels) and stimulates plant cells to undergo unregulated (cancerous) growth, leading to gall production.
Galls become visible anywhere from several weeks to one or more years after the time of infection.
How do I save a plant with crown gall?
There is no cure for crown gall once galls begin to form.
Galls can be pruned away, but new galls may reform elsewhere on the plant.
How do I protect plants at planting from crown gall?
Use disease-free stock from a reputable nursery and inspect the roots and crowns for galls before planting.
Nogall™ is a biological control product that can prevent new infections of crown gall disease on stone fruit trees, nut trees and roses at the time of planting.
When susceptible plant material is dipped in a suspension of Nogall prior to planting, the Nogall K1026 bacteria act by colonizing the wounds and producing antibiotics, which inhibit the disease pathogen. (Note: Nogall containing K1026 is generally ineffective against strains causing crown gall disease in grapes and some ornamentals.)
Current biological control products contain A. radiobacter, a close relative of the crown gall disease organism. This new strain is one of the first live genetically engineered organisms that is EPA registered for sale to the public.
Stonefruit orchardists have used Nogall for many years and may have become too familiar with it. Read and follow the directions, and take the time to treat the trees—Nogall is a live organism, treat it with care—it's only once every 15 years!

See this article in Tree Fruit June 2018

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