Symptoms and Control Methods of Cherry Blossom Shot Hole Brown Spot Disease

Symptoms and pathological changes: This disease mainly occurs on mature leaves. When the disease develops, it gradually spreads from the lower leaves upward. It begins with needle-tip-sized purple-brown spots appearing on the leaf surface, then the lesions expand into concentric round brown spots 3-5 mm in size, and a light brown abscission layer forms at the edge of the lesions. Later the lesion area falls off, leaving small holes on the leaves; sometimes two or three lesions merge into an irregular shape. On the surface of old lesions, numerous gray-black small granular conidiophores can form. Besides harming cherry blossoms, this disease also harms peach, purple-leaf plum and other Rosaceae flowering trees. It not only affects ornamental value, but can also cause early defoliation and poor growth and development. The pathogen of this disease belongs to the ascomycete fungi. It overwinters on the tree as ascocarps, and in the second year ascospores form inside the ascocarps, disperse and spread after maturing, germinate and infect healthy leaves. It generally begins to develop in June, and reaches its peak in August and September.

Control methods: 1. Collect and burn diseased leaves to eliminate the source of infection. Strengthen maintenance and management to enhance the disease resistance of the plants. 2. Starting from the initial leaf expansion of cherry blossoms, spray once every 7-10 days with 500x zineb solution, 1000x thiophanate-methyl solution, or an equal-amount 200x Bordeaux mixture, for several consecutive applications, to prevent the disease.

Control Methods for Cherry Blossom Shot Hole Brown Spot Disease

Cherry blossom shot hole brown spot disease:It occurs from May to June. Purple-brown small spots appear on the leaves, then gradually expand into round shapes. After the lesion areas dry and shrink, they become small holes. The pathogen mostly overwinters on diseased branches and diseased leaves. The optimum temperature for development is 25°C to 28°C. It spreads by wind. In rainy seasons it is favorable for infection and disease development. When the tree vigor is weak, drainage is poor, and ventilation and light penetration are poor, the disease occurs severely.

Control methods:

（1）、Strengthen cultivation management, carry out reasonable pruning and trimming, and pay attention to cutting off diseased shoots. Promptly clean up and burn diseased leaves to create clean growing conditions for the plants.

（2）、Before new shoots sprout, spray 3-5 degrees Baumé lime sulfur mixture. During the disease period, spray 160x Bordeaux mixture or 50% benomyl wettable powder at 1000x to 2000x, or 15% zineb at 600x to 800x.

Cherry Blossom Brown Spot Shot Hole Disease

   [Distribution] Cherry blossom brown spot shot hole disease is an important disease of cherry blossom leaves, and occurs in all cherry blossom growing areas in China.

   [Symptoms] It mainly harms mature leaves, and also harms young twigs. Infected leaves first show needle-tip-like purple-brown small spots, which soon expand into round to nearly round spots, 1-4 mm, brown in the center with slight concentric rings, purple or red-brown at the edges, and gray-brown fuzzy small spots appear on the lesions. Later, an abscission layer forms around the lesions, brown mold-like material appears on both sides of the diseased leaves, and the center of the lesions dries up and falls off, forming round small holes and creating shot hole spots. When several lesions overlap, the shot holes are irregular. Lesions can connect with each other. When there are many lesions on a leaf, the leaf falls off early.

   [Pathogen] The pathogen is a fungus, Cercospora circumscissa. The conidiophores are densely aggregated into bundles. The conidia are whip-shaped to obclavate, olive-colored, straight or slightly curved, with 1-7 septa.

   [Disease pattern] The pathogen also harms peach, plum, apricot, Japanese apricot and many other woody flowering plants. The pathogen overwinters in diseased twigs and diseased fallen leaves. Ascospores mature in spring, and when the temperature is suitable the following year they spread by wind and rain. It generally starts from the lower leaves in June, and August to September is the peak period of disease development. When there is much wind and rain, the disease is severe. By late September only a small number of leaves remain on the plants. Conditions such as poor ventilation, dense planting, and weak tree vigor all favor severe occurrence of the disease. In summer drought, when tree vigor is weak, the disease incidence is also relatively high.

   [Control methods]

 (1) Chemical control: Before and after leaf expansion (especially for seedlings), spray 65% zineb at 500x, or 3-5 degrees Baumé lime sulfur mixture, or 1:1:100-200 Bordeaux mixture, etc. Alternatively, before budding, spray 2-3 degrees Baumé lime sulfur mixture, or 1% Bordeaux mixture, to disinfect the tree. Before leaf expansion, spray 1.02-1.04 kg/L lime sulfur mixture. After leaf expansion, spray 50% carbendazim at 800x, or 70% thiophanate-methyl at 1500x, or other fungicides. For bacterial shot hole disease, after leaf expansion spray zinc sulfate lime solution (zinc sulfate 500 g, slaked lime 2000 g, water 120 kg).
 (2) During the disease period, spraying 50% benomyl wettable powder at 1500x, or 65% zineb at 600x, or 50% carbendazim at 1000x all have good control effects.
 (3) Strengthen cultivation management, create good ventilation and light penetration conditions, apply more phosphorus and potassium fertilizer, and enhance disease resistance. Do not plant cherry blossoms in wind tunnel areas, and water promptly during drought.
 (4) Clean the courtyard, remove and burn diseased fallen leaves in autumn, and combine with pruning to cut off diseased branches, reducing the source of infection for the coming year.