Symptoms and Control Methods of Cherry Brown Spot Disease
Cherry brown spot disease, also known as cherry brown spot shot hole disease, is an important disease of cherry leaves. It was reported early in Japan and other countries. It occurs commonly on cherry trees in various regions of China, including Nanjing, Taiyuan, Tianjin, Shanghai, Chengdu, Xi'an, Suzhou, Jinan, Changsha, Lianyungang, Wuhan, and Taiwan, China, among other provinces and cities, with severe outbreaks in Wuhan, Chengdu, and Tianjin. Infected cherry leaves develop shot holes, which not only affects their ornamental value but also causes premature defoliation, affecting the plant's growth and development. The disease also attacks cherry, Japanese apricot, peach, and other stone fruit ornamental trees.
Symptoms: Brown spot disease mainly damages cherry leaves, and sometimes also infects young shoots. In the early stage of the disease, pinhead-sized spots appear on infected leaf surfaces. The spots are purplish-brown and gradually expand to form circular or nearly circular lesions. The lesions are brown to grayish-white, with purplish-brown margins, and can reach 5 mm in diameter. In the late stage of the disease, grayish-brown scattered structures, namely the pathogen's conidia and conidiophores, develop on the lesions. Finally, the center of the lesion dries up and falls off, forming a shot hole with neat edges. In severe cases, the leaves are covered with shot holes, causing defoliation.
Pathogen: The pathogen is Cercospora circumscissa Sacc., belonging to the phylum Deuteromycota, class Hyphomycetes, order Moniliales, genus Cercospora. The sexual stage is Mycosphaerella cerasella Aderh., belonging to the phylum Ascomycota, class Loculoascomycetes, order Dothideales, genus Mycosphaerella. However, the sexual stage is rarely seen in China.
Disease cycle: The pathogen overwinters as mycelium in the diseased parts of branches and shoots of infected plants, or as perithecia on fallen diseased leaves. In the spring of the following year, conidia are produced, and the spores are spread by wind and rain, entering the host through stomata. The disease usually starts first on the lower part of the tree canopy and gradually spreads to the upper part. Disease severity is high in windy and rainy years; when plants are planted too densely, the disease is prone to occur; on poor, thin soil, the disease occurs severely; in summers with drought, weakened tree vigor leads to severe disease as well. Tree species such as Japanese cherry and Japanese late cherry have weak disease resistance and suffer severe infections.
Control: (1) Reduce sources of infection: In winter, along with pruning, clear away dead branches and fallen leaves, cut off diseased branches, and destroy them in a centralized manner. (2) Strengthen management: Apply more organic fertilizer and phosphorus and potassium fertilizers, and irrigate promptly, especially during dry seasons, to improve plant disease resistance and control the occurrence of the disease. Match tree species to suitable sites, and avoid planting cherry trees in wind tunnel areas. (3) Chemical control: Before cherry buds break, spray Bordeaux mixture at 1:1:160, or lime sulfur mixture at 2-3 degrees Baume to prevent infection. During the disease period, spray 65% zineb wettable powder at 500-800 times dilution, or 70% thiophanate-methyl wettable powder at 800-1000 times dilution. Spray once every 10-15 days, for 2-3 applications.