How to prevent and control brown spot and shot hole disease in cherry blossoms

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

[Symptoms] It mainly affects mature leaves and also affects young twigs. Infected leaves first show pinhead-sized purplish-brown dots, which soon enlarge into circular to nearly circular spots, 1-4 mm, brown in the center, slightly with concentric rings, with purple or reddish-brown edges, and grayish-brown fuzzy dots appear on the lesions; later, an abscission layer forms around the lesions, brown mold-like growth appears on both sides of the diseased leaves, and the center of the lesion dries up and falls off, forming round small holes and producing shot hole spots. When several lesions overlap, the holes become irregular. The lesions may connect with one another, and when there are many lesions on a leaf, the leaf drops early.

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

[Disease occurrence pattern] The pathogen also affects many woody ornamental plants such as peach, plum blossom, apricot, and plum. 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. Generally, disease begins on the lower leaves starting in June, and August to September is the peak period of disease occurrence. When there is much wind and rain, the disease is severe, and by late September only a small number of leaves remain on the plants. Conditions such as poor ventilation, dense planting, and weakened 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 500-fold solution, or Baume 3-5 degrees lime sulfur mixture, or 1:1:100-200 Bordeaux mixture, etc. Alternatively, before bud break, spray Baume 2-3 degrees 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 800-fold solution, or 70% thiophanate-methyl 1500-fold solution, or other fungicides. For bacterial shot hole disease, spray zinc sulfate lime solution after leaf expansion (zinc sulfate 500 g, slaked lime 2000 g, water 120 kg).

(2) During the disease period, spraying 50% benomyl wettable powder 1500-fold solution, or 65% zineb 600-fold solution, or 50% carbendazim 1000-fold solution all have good control effects.

(3) Strengthen cultivation management, create good ventilation and light conditions, apply more phosphorus and potassium fertilizer, and enhance disease resistance. Do not plant cherry blossoms in windy outlet areas, and water promptly during drought.

(4) Clean the courtyard, remove diseased fallen leaves in autumn and burn them, and prune out diseased branches along with pruning to reduce the source of infection the following year.