What is bacterial rose canker and how to treat it?

One of the most dangerous bacterial diseases affecting roses is bacterial canker. Many gardeners, upon detecting symptoms, refuse to treat affected plants.

This approach is largely justified: the complexity of treatment, the severe consequences, and the contagious nature of the disease make it advisable to eliminate the sources of infection. However, in its early stages, bacterial canker of rose bushes is curable, although there is no guarantee of a positive treatment outcome.

Signs and causes of bacterial cancer

There are two rose diseases called bacterial canker, but they are caused by different pathogens. In both cases, the plants will suffer serious damage, potentially leading to the death of the bush. A more dangerous form of the disease is canker, which affects the rose roots.

Bacterial root canker

The disease is caused by the soil-dwelling bacterium Agrobacterium tumefaciens. The microorganism can enter the soil through water, infected seedlings, or garden tools during digging and tillage. The bacterium can survive outside the plant for 3-4 years. The microorganism penetrates rose tissue only through cracks or cuts, so root damage due to replanting, careless tillage, or infestation by soil-borne pests (mole cricket, cockchafer larvae, and others) is a prerequisite for the development of rose root canker.

The pathogen causes chaotic cell division, resulting in the growth of lumpy growths on the roots and root collar. Rarely, these growths can even appear on the stems. These growths can be of any shape and size, and over time, they expand and rot. Consequently, the blood vessels in the root tissue are destroyed, impeding the flow of moisture and nutrients from the soil to the upper part of the bush. The disease can be suspected by a deterioration in the overall health of the plants: the roses become weaker, their growth slows, and eventually the bush dries out.

The difficulty in diagnosis makes the disease particularly dangerous—the symptoms that appear on the above-ground portion of the bush are nonspecific. The characteristic swellings on the root collar, which usually give gardeners an idea of ​​the cause of the bush's weakening, appear when the root system is completely affected by the disease.

The stage of the disease can be determined by the growths on the roots. Newly formed swellings are light-colored and soft, but gradually they harden, acquiring a woody texture and a darker hue. In the late stages of the disease, the growths begin to rot.

The development of bacterial cancer in roses is promoted by:

1. Temperatures range from +25°C to +30°C. When temperatures rise to +38°C, the pathogen becomes inactive.
2. Soil acidity should be between pH 6 and 9. When introduced into acidic soil, the bacteria remain viable, but the disease does not develop.
3. Clay soil. When growing in heavy soils, root cracks are more likely to develop. This can occur if the soil is too dry or too wet.
4. Excess nitrogen. Rapid and intense plant cell growth due to excessive doses of the element leads to thinning of their cell membranes. As a result, the cell's defenses against bacterial and viral penetration are weakened.

Bacterial stem canker

Stem canker is caused by the bacterium Pseudomonas syringae. The pathogen can enter the plant through air, water, pruning tools, or grafting buds that haven't been disinfected after handling the diseased plant. The infection is also transmitted by insects.

The bacterium tolerates low temperatures well, overwintering in plant tissue and becoming active with warmer temperatures. Bacterial canker on stems most often appears and begins to progress rapidly in early spring, when roses are weakened. Infection by this type of bacterial canker requires damage to the stem bark. Excessive soil moisture and weakened rose immunity due to poor overwintering contribute to the disease's development.

On young stems, sunken areas develop, and brownish-brown ulcers appear under the bark. Over time, the bark in these areas dies, and the entire stem gradually dries out. A related symptom of stem canker is the appearance of dark, water-soaked spots on the leaves. If the weather is dry, the center of these spots dries out, and the leaf cracks. During periods of rain, the black spots expand until they cover the entire leaf blade. The leaf then falls from the bush.

Treatment methods for rose cancer

Regardless of which of the two diseases affects roses, treatment is only effective in the early stages of cancer. If the disease has progressed significantly, the rose must be destroyed. Excavated bushes, as well as any removed sections of the plant, must be burned to prevent the bacteria from spreading throughout the garden or flowerbed.

Treatment of root cancer

If treatment is inadequate, there is a risk of transferring bacteria to a new location during replanting. Therefore, when choosing to save a bush, a gardener must weigh all the risks and benefits of such a step.

Treatment regimen for bacterial root cancer:

• The affected bush should be dug up and the roots washed with water, and then rinsed with a strong solution of potassium permanganate.
• Root shoots where growths have appeared should be trimmed back to healthy areas. After each cut, the knife should be disinfected with alcohol.
• The roots of the bush remaining after pruning should be immersed in a 1% solution of copper sulfate for 2-3 minutes.
• Rinse the roots with clean water.
• Treat the cut areas with alkyd paint. Let dry.
• Dip the roots in a mixture of sand and clay (thick consistency).

• Plant the bush in a new location.

Treatment of stem cancer

Small affected areas on the stems should be trimmed, cleaning the cuts down to healthy tissue. If the leaves are damaged, the entire stem should be cut off 10 cm below the last spotted leaf. The cuts should be disinfected with 5% copper sulfate and sealed with drying oil.

Even if the "surgery" is successful, the disease doesn't resolve immediately; regular treatment will be required for approximately three more years. During this period, it is necessary to:

1. Regularly inspect the bushes and, if necessary, repeat the pruning procedure for damaged areas.
2. In the spring (before the sap starts to flow), treat the bush with Bordeaux mixture (2%) or the drug "Nitrofen" (200 g of the product should be diluted in a bucket of water).
3. After spring treatment, spray the rose with a solution of zinc sulfate (3 g per 10 liters).
4. At the end of summer, feed the plant with an additional dose of potassium. For watering, prepare a solution of 30-40 g of potassium sulfate or 20 g of potassium nitrate per 10 liters of water. For spraying, dilute 10 g of each substance in the same volume of water.
5. Before covering the rose for the winter, the bushes need to be sprayed with a 2% Bordeaux mixture.

Preventive measures

General preventative measures that are effective against both types of cancer include strengthening the plant's immunity and resilience. Proper care of roses is sufficient for this.

Furthermore, to prevent bacterial and viral infections, it's important to follow sanitary rules. All tools should be disinfected with alcohol, and plant cuts should be treated with garden pitch or potassium permanganate.

Prevention of root cancer

Even if the soil in your garden is contaminated with bacteria, it doesn't mean the disease will develop. The lifespan of the rose root canker pathogen is 3-4 years. If the bacteria doesn't find a host plant during this period, it will simply die. Therefore, the following guidelines are recommended for rose care:

• Do not plant rose bushes in areas where this or other crops susceptible to bacterial root canker were grown less than 5 years ago.
• Avoid planting roses near potentially susceptible plants. Conversely, sowing cereals in the flowerbed reduces the risk of disease.

• Remove soil pests.
• Give the last nitrogen fertilization no later than mid-June.
• Install winter shelter only in dry weather.

Prevention of stem cancer

Gardeners have more options for preventing this disease. Since the disease affects the above-ground portion of the bush, preventative treatments with pesticides are effective. These treatments are carried out twice a year: in the spring, before bud break, and in the fall, before placing the roses under cover.

Effective means:

• copper sulfate (1%);
• Bordeaux mixture (2%);
• copper oxychloride (0.4%);
• the drug "Topsin-M" (0.2%);
• "Nitrofen" (2%).

Additionally, it's important to perform annual pruning during the dormant period. This can be in spring or fall, but there should be no sap movement during this time. Bacteria introduced into the bush tissue during pruning will spread more quickly through the plant along with the sap.

Resistant varieties

There are no rose varieties that are unequivocally resistant to stem and root canker. However, shrub roses are much less likely to be affected by bacterial root canker than climbing roses. It has also been noted that garden roses are highly susceptible to stem canker.

Tips and reviews from gardeners

Anastasia, 36 years old:

"Root pruning helps. My bush even bloomed again, although the flowers were very small and few in number. But I was prepared for the bush to be destroyed. Incidentally, there's no written instruction on how to properly dig up diseased plants. If a bush is damaged by stem cancer or any fungus, before removing it from the ground, I personally cut off the diseased leaves and branches, disinfect my tools and hands, and then dig up the roots. This way, we minimize the risk of spreading the infection to other plants."

Elena, 48 years old:

"After encountering bacterial canker on my rose roots a few years ago, I wondered what to do about the infected area. Here's my experience: pour several buckets of boiling water on the affected plant, which should kill the bacteria. You can also acidify the soil (but this limits the number of plants that can grow in that spot). A solution of citric acid or vinegar works well for this. I dilute 2 tablespoons of acid or 100 ml of vinegar (9%) in a bucket of water. I pour one bucket per square meter of area. I find peat to be a weak solution for killing bacteria, but it's more beneficial for the soil."

Maria, 51 years old:

"There have been cases of purchasing infected planting material, so I now treat the seedlings with antibiotics. I usually use Cefotaxime for this, diluting 1 gram in a liter of water. The seedling should be completely immersed in the resulting solution and soaked for about an hour. Cancer pathogens, like any bacteria, are vulnerable to such agents. I haven't had any similar problems since."

Olga, 40 years old:

"I had a rose with bacterial canker growing in my flowerbed, surrounded by other plants. I removed the bush, but I didn't dare light a fire there or do anything with the soil because of the surrounding plants. Ultimately, I removed the old soil and replaced it with fresh. I decided to plant ornamental grasses in the area during the quarantine—it's beautiful, and grasses are immune to this infection."

Bacterial root canker can be controlled, but treating and preserving only the most valuable plants makes sense. The chances of saving rose bushes are significantly higher if they are infected with bacterial stem canker, but it's important to continue treatment for several years. In both cases, the key to managing the disease is prevention.