Monday, June 17, 2019

Crown Gall In Your Rose Garden

Crown Gall growing on Tournament of Roses

Agrobacterium tumefaciens and your roses
Joe Truskot, Master Rosarian

Basic Questions
What are galls?
 Outgrowths of plant tissue, Reprogrammed cells, Tumors, Not parasitic growths like mistletoe
What causes galls to form on many plants?
Insects including wasps, aphids, flies, various fungi, bacteria and viruses
What causes galls to form on roses?
Bacteria in the soil, Agrobacterium tumefaciens
Which roses are most susceptible?
Roses in the ground for more than 3 seasons, grafted roses (more so than own root), bare root roses with broken prominent roots, dug up and transplanted roses
How do the bacteria enter the bush?
Weak grafts, injured roots, frost damage, and, unintentionally, moles other ground diggers
What are the signs of a crown gall infestation?
Decreasing performance, fewer basal breaks or strong canes, decline in candelabras or flower sprays,
Small/spindly canes from the bud union, lack of normal vigor, sudden death of major canes, food/water/ sunshine – don’t help

Stem gall on a rose cane and root gall on lower root
Options and Remedies
Do nothing.
No cure - but it grows slowly, too late for amputation, vigorous roses will live for years with it, hardened galls are safe houses for earwigs and insect larvae
Do surgery.
Sharpen your hatchet, scrape down to the greenwood, disinfect with vinegar, alcohol or bleach solutions
Dig up and discard.
Remove affected plant/galls/soil, salvage what you can, make cuttings in fresh soil, add plenty of green manure to the area, plant annuals and cereal grasses from seed, let 2 or 3 years go by before planting roses in that spot
Biological Control.
Galltrol uses a strain of freshly grown Agrobacterium radiobacter
Commercially available Gallex.
Dig all around the base and discard soil, remove as much of the gall as possible, leave exposed for two days, paint on the Gallex and let dry for 2 days, replace with fresh soil
Buy a new rose.
Prepare new roses.
Soak bare root roses in a weak bleach solution (1/4 cup bleach to 5 gallons of water), kills surface bacteria/insect eggs, rehydrates the bush
Remove Bindweed.
Wild morning glory can serve as a host (bindweed, Ipomoea leptphylla), birds eat the fruit and scatter the seeds, bacteria clings to bindweed roots
Help the rose defend itself.
When injured, plants release phenolic compounds. Phenols are sent to the injured area to heal the wound. Most plant scars are a result of the phenols in action. Hungry, thirsty roses can’t produce enough phenols.
Where do phenols exist?
Phenols are present in the food we eat, found in plants used in traditional medicine, some phenols are germicidal and used in disinfectants
Healthy soil is inviting to surface critters as well as earthworms, grubs and a panoply of microbes below ground

Components of Healthy Soil
Sandy loam:
Good drainage, adequate air circulation, easy for rose roots to grow, composition is 50-70% sand, 15-20% clay, and 15-20% silt
Organic material:
Controls pH factor, provides nutrients, retains moisture
Microbial action:
Breaks down organic material, provides environment for earthworms, warms the soil, certain bacteria and fungi help a rose’s immune system, protect against pathogens and other threats, fungi colonize plant roots and create mycorrhizae which greatly extend the reach of the roots
Microbes in Healthy Soil:
Part of a rose’s digestive system, recycle water and break down nutrients, overuse of chemical fertilizers and pesticides harms microbes
What do mycorrhizae do?
Mycorrhizae help similar plants communicate, produce chemicals that repel pests and attract predatory insects, mycorrhizae are covered with a protein called glomalin which is composed of 30 to 40 % carbon. Glomoalin fixes carbon in the soil. Ninety percent of all organisms on the planet live underground.
What are bacteria?
One-celled microscopic organisms are oblong and rod-like, one teaspoon of healthy soil contains from 100 million to 1 billion bacteria, bacteria dots the surface strands of fungi
What are the four bacteria groups?
Decomposers: convert energy in soil organic matter into forms other organisms can use
Nitrogen fixers: from air to soil
Chemoautotrophs: obtain energy from other than carbon (nitrogen, sulfur, iron, hydrogen)
Pathogens: includes Agrobacterium tumefaciens which create galls
What do bacteria do?
All four groups of bacteria help water retention and the movement of water in soil, nitrogen fixing: from air to soil, nitrifying: converting ammonia to nitrite, denitrifying: anaerobic (water-logged soil) release nitrogen, release stored energy in the form of heat
What are actinomycetes?
More highly evolved than bacteria but not quite a fungus, best at hard to degrade cellulose and chitin at high pH levels, the smell of healthy organic soil means actinomycetes are present
What are the benefits of Agrobacterium tumefaciens?
Scientists have converted (“disarmed”) it into efficient delivery systems for genetic manipulation. The transgenes must be stably integrated in the host genome. Agrobacteria largely modify the host, particularly its defense-related genes. Agrobacteria largely shift the “hormone balance” in their infected hosts. This effect on endogenous growth regulators will ultimately lead to agrobacterium-induced tumor formation. This property makes genetic modification possible


  1. Great read. You gave options, but what do YOU usually do when your favorite rose becomes infected by crown gall? I used to dig them up and dispose of them but the solution for me is becoming less obvious as it seems it hasn't prevented the disease from appearing again and again in newer roses. I don't want to keep digging them up, but also don't want my yard to be a breeding ground for the bacteria.

    1. Also, it's interesting that you say own-root roses are less susceptible because it seems like a much higher percentage of my own-root get it than the ones grafted onto Dr. Huey.

  2. Apologies for the VERY late response. I just noticed your comments regarding Crown Gall. My own root roses were all cuttings that I made of roses I liked. So their roots were never damaged and the coating on the roots stayed intact through the various upgrading of pots and then placement in the ground. I found crown gall on a rose which was close to a water leak under my house. I watched the gall grow on this bush by leaps and bounds. Once the leak was fixed,and before the dirt was put back,I took a shovel, positioned it carefully right where the gall was growing and stepped hard on it. The gall broke off. It seemed to be mostly growing on one side. So I used my hori hori knife and scraped as much of the gall off, bathed the wound in vinegar and put some fresh soil close to the bud union. So far this year, the rose has continued to produce blooms. I don't know that I'll ever be rid of it, but as long as I can continue my surgery and the roses do well, I'll let good enough alone.

    1. Mine with crown gall also produced blooms, but their vigor just wasn't the same as before and they were just taking up space. I decided to dispose of my diseased plants, and am planting new ones in fresh potting soil in pots (I always like a good excuse to acquire new plants). Whenever a plant had a visible crown gall above ground, it was always accompanied by many more galls in the roots- I think the infection rate may be more severe in my soil. Happy Gardening Joe!