Occurrence patterns and control methods of black locust canker disease

Black locust canker disease is a major trunk and branch disease of black locust (Robinia pseudoacacia), affecting both young and mature trees. The disease mostly occurs in the bark of the main trunk. After trees are affected, lesions of varying sizes mostly appear on the lower part of the main trunk and at branch forks, and the lesions are spindle-shaped, oval or irregular. On young trees, the diseased part of the main trunk is cankerous and slightly sunken; on large trees, the bark of the main trunk is thick, and the diseased part is water-soaked with no obvious sunken areas. The disease spreads faster lengthwise than crosswise. When the diseased area encircles the trunk completely, the tree withers and dies. In the later stage, white and orange-red conidial masses are often produced at the lenticels and bark cracks of the diseased part.

The pathogen is Fusarium, a soil-inhabiting fungus, which can also overwinter in diseased tissues. Factors such as poor and thin soil, a high groundwater table or drought, low-temperature attacks in winter or early spring, and windward openings can all cause tree decline, weaken the tree's stress resistance, and lead to the occurrence of the disease. Rainy summer seasons easily cause the disease to become epidemic. The pathogen spreads by wind and rain, invading and spreading through wounds, lenticels and other pathways. June to August is the peak period of incidence.

Control methods. Strengthen the tending and management of black locust stands to enhance tree vigor and improve disease resistance; prevent damage to the trunks; for small areas of young black locust plantations, in the early stage of the disease, spray the trunks with 55 degrees Baume lime-sulfur mixture or 1:10 alkaline water.