Crown gall is a bacterial disease that causes plants to dark, warty growths, typically near the graft union or on a forking branch. It is a common disease for rose bushes and some fruit trees. The disease attacks the plant tissue under the bark and can deform the plant’s shape.
One of the most noticeable features of crown gall is its irregular, often cone-shaped growths at or near the base of a stem. These growths can be as small as half an inch or as large as three inches across. They are usually reddish-brown but we have seen them appear to be almost grey. The growths tend to be jagged and warty.
What are the symptoms of crown gall on roses?
There are a few other symptoms, in addition to the growths:
- As mentioned previously, the gall or growth itself, which sometimes looks like a misshapen pine cone
- Stunted growth in the entire bush, primarily in the biggest canes
- Wilting and death of the bush, with a distinct yellowing of part or all of the cane
What causes crown gall on rose bushes?
According to the American Phytopathological Society, crown gall is caused by the bacterium “Agrobacterium tumefaciens,” which can thrives in soil. The bacterium can affect other plants in the garden, not just roses. This is why it is very important to be careful not to compost crown gall infected plants in your regular compost.
The pathology of this bacterium is beyond the scope of this site, but suffice it to say that the bacterium stimulates certain proteins to invade the plant tissue and cause uncontrolled cell division, sort of like the way cancer operates in human cells. However, there is no physical connection between gall and human cancer–it is only a metaphor.
Getting rid of crown gall
In the Pacific Northwest, roses are practically a normal aspect of life. Thousands of people visit Portland every year just to visit our iconic rose gardens. However, roses are also susceptible to a number of diseases and conditions that can cause significant damage to your garden and other plants if not treated quickly.
Most often noticed in winter or spring
In roses, this gall is most easily seen in winter or spring, after the bush has been pruned and leaves have come off or been removed. Unfortunately, if the gall has been growing on the shrub throughout the primary growing season, it has had time to infect much of the shrub.
How to spot the early signs of crown gall
The main symptom of crown gall is root swelling, which can be detected early, if you go around digging up your plants. With roses, thorns tend to discourage us from doing that kind of thing, so it can be tough to see the crown gall early. That said, if you notice yellowing canes, especially near the soil, or wilting leaves on some yellowing canes, you may want to check for gall.
How to remove crown gall
There is really only one way to deal with gall, and that is physical removal:
- Locate the gall on the plant.
- Using sharp bypass pruners or loppers, cut the cane of the affected bush below the actual occurrence of the gall tumor. If possible, prune the branch back at least one inch or more from the boundary of the gall tumor.
- If the gall has encircled much of the crown, or the graft union, of the plant, you may need to remove the entire plant. If so, be sure to dig out as much of the root system as possible.
- Dispose of any plant debris and soil, but not in your compost pile. If possible, you should incinerate the infected plant, but make sure that you protect your eyes and lungs by wearing protective clothing. The fungus may float on the smoke and be inhaled. Although it is unlikely to cause you any problems, it’s best to take precautions.
- If you cannot incinerate the infected plant or gall tumors, then dispose of them in your garbage bin, where it is less likely to be added to a community compost pile or chipped into mulch.
- Disinfect your tools/loppers/pruners/clippers with a solution of 1 part isopropyl alcohol to 10 parts water. We like to keep a solution in a one quart spray bottle near our garden tools. Crown gall can easily be spread to other plants if you neglect to disinfect your tools!
Note: Some rose gardeners swear that the use of WD-40 sprayed on the newly pruned canes below a gall tumor will prevent any of the bacterium from spreading. However, there is no research or evidence, other than anecdotes, to confirm the efficacy of WD-40 as a crown gall stopper.
Some rose varieties may be more susceptible
Crown gall may impact certain species–mainly older rose varieties–or bushes in certain locations. This could be because the bacterium is well established in that location. It’s a good idea to keep a garden diary when it comes to diseases, especially one like crown gall. If, for example, you note that a particular rose bush is infected with crown gall every year, you may want to remove and destroy that bush and the soil around the roots where it was planted. Then, leave that area fallow for two or three seasons before replanting. Of course, you can only do this in the most ideal circumstances. Most of us don’t have the luxury of leaving a large blank spot in our gardens. If you really must plant something in that spot, plant a different type of shrub than a rose.
How to Get Rid of Crown Gall Once and For All
Unfortunately, there’s no way to guarantee that you can remove crown gall forever. The soil is full of various bacteria, many of which are beneficial to plant life. And we have no way of knowing whether or not animals or invertebrates carry these bacteria and leave them in the soil as they pass by. The best prevention is to inspect your plants carefully from time to time and to keep track of how they look and how healthy they are during each growing season. Remove any diseased plants or diseased parts of plants and dispose of the diseased plants properly. There is no spray or fungicide that works against crown gall.
Besides roses, other plant species that are most at risk for crown gall infection include apples, tomatoes, and grapes, but many varieties of shrubs and plants can get infected. Fortunately, these species do not often sport thorns and are much easier to inspect during the growing season.