Symptom Identification and Integrated Control Methods for Crown Gall Disease in Chrysanthemums

Crown gall disease in chrysanthemums is a common bacterial disease in chrysanthemum cultivation, mainly affecting the root crown and root system of the plant. In the early stages of the disease, small white or slightly flesh-colored tumor-like protrusions appear on the affected parts, with a smooth surface. As the disease progresses, the tumors gradually enlarge and harden, turning brown to dark brown with a rough surface, and often cracking in the later stages. The above-ground parts of affected plants show weak growth, with leaves turning yellow and becoming smaller, branches becoming thin and weak, and flowering quality declining. In severe cases, the entire plant can wither and die. The pathogenic bacteria can survive for long periods in the soil or on diseased plant residues, and spread through rainwater, irrigation water, agricultural operations, and contaminated seedlings. The bacteria mostly enter through wounds caused by transplanting, pruning, or feeding damage from underground pests. Areas that are warm and humid, low-lying, with heavy clay soil, and under continuous cropping for many years tend to have more severe disease outbreaks. For control, the basis should be cultivating and using disease-free seedlings. Before planting, disinfect the seedling substrate and seedbeds to reduce contamination opportunities at the source. Handle transplants gently to avoid damaging the root system as much as possible, and promptly control underground pests to reduce wounds for bacterial entry. In routine management, pay attention to disinfecting farm tools, water reasonably, avoid prolonged waterlogging in the field, and maintain good soil aeration. When diseased plants are found, they should be promptly dug out with roots, taken out of the field for centralized destruction, and the soil in the planting holes should be disinfected to prevent the bacteria from spreading to surrounding areas. In heavily affected plots, rotation with non-host crops such as grasses can be used, combined with measures such as improving the soil and applying fully decomposed organic fertilizer to enhance plant vigor and reduce disease occurrence. In addition, crown gall disease should be distinguished from root-knot nematode damage. Crown gall disease forms tumor-like growths, while root knots caused by nematodes often contain tiny nematodes visible inside. Only with accurate diagnosis can the right treatment be applied to achieve the desired control effect.