What are the symptoms of crown gall disease in roses? What should be done?

Crown gall disease, also known as root crown gall disease, is one of the most common root diseases on garden flowers and nursery stock. Plants such as roses, cherry blossoms, peaches, and roses are all easily attacked by it. So what are the symptoms of crown gall disease in roses? What should be done?

1. What are the symptoms of crown gall disease in roses?

Crown gall disease in roses mainly damages the root crown, main roots, and lateral roots of roses, while on rose nursery stock it mostly occurs where the scion and rootstock heal together. In the early stage of the disease, nearly round small tumor-like growths appear, which then gradually enlarge, harden, develop a rough surface, crack, and change in color from light to dark brown or blackish brown, with the interior of the gall becoming woody. The galls vary in size; large ones may be as big as a fist or larger, and the number ranges from a few to more than a dozen. Because the root system is damaged, diseased rose plants grow slowly, and in severe cases the entire plant dies. The disease is very stubborn; even if the galls are removed, they can often grow again.

The pathogenic bacteria overwinter in the cortical layer of the tumor tissue, or when the tumor tissue rots and breaks open, the bacteria mix into the soil. The gall-causing bacteria in the soil can also survive for more than 1 year. The bacteria spread through water flow, underground pests, grafting tools, farming implements, and other means, and diseased flower and tree seedlings and cuttings can be spread over long distances through transport. The bacteria invade the host through wounds. Insect wounds, mechanical injuries caused during cultivation, cut ends of cuttings, grafting wounds, and other injuries can all become routes for the bacteria to invade.

2. What should be done when crown gall disease appears in roses?

1. In rose cultivation, avoid as much as possible creating any wounds that are favorable for the bacteria to invade. The cleft grafting method commonly used in rose grafting creates relatively large wounds and comes into contact with bacteria-carrying soil, making it the most susceptible to disease. Therefore, using bud grafting instead of cleft grafting is beneficial for the prevention and control of crown gall disease.

2. Damage by underground pests causes root injury and increases the chance of disease. Timely control of underground pests can reduce the chance of disease.

3. Choose disease-free soil for the nursery and avoid continuous cropping. Orchards and nursery sites where crown gall disease has occurred cannot be used as seedling-raising land. Nursery land should be disinfected; apply 50-100 grams of sulfur powder or 60 grams of 50% formalin per sq m.

When grafting seedlings, avoid letting the wounds touch the soil. Grafting tools must be disinfected with 75% alcohol before and after use. It is best to change from stem grafting to bud grafting.

For alkaline soil, appropriately apply acidic fertilizer or increase the application of organic fertilizer to change the soil pH value and make it unfavorable for bacterial growth. Drain promptly during the rainy season and improve soil aeration. When cultivating, injure the roots as little as possible.

4. Diseased seedlings must be treated with medicinal solution before planting. You can choose to soak them in a 500- to 2000-fold streptomycin solution for 30 minutes or in a 1% copper sulfate solution for 5 minutes. Diseased plants can be irrigated with a 300- to 400-fold “402” solution, or after removing the tumor, apply 500- to 2000-fold streptomycin or 500- to 1000-fold oxytetracycline to the wounds.