Symptoms and Control Methods of Hydrangea Anthracnose

[Distribution] Tianjin, Hebei, Liaoning, Henan, Guangdong, Shanghai, Jiangsu, Zhejiang, Fujian, Sichuan.

[Symptoms] Mainly occurs on leaves. The lesions initially appear as small brown spots, which after expanding become circular, with edges from purplish-brown to blue-black, and centers from light brown to grayish-white, with concentric rings and whorled small black dots protruding. Lesions vary in size, the small ones only 1 mm, and the large ones up to 10 mm.

[Pathogen] The pathogen is a fungus, Colletotrichum hydrangeae (Colletotrichurnhy-drangeae), Deuteromycotina, Melanconiales. Acervuli black, setae sparse, conidia elliptical.

[Disease Development] The pathogen overwinters as mycelium or acervuli on diseased plant debris, produces conidia the following year, spreads by wind and rain, and mostly infects through wounds; repeated infection can occur during the growing season. The disease period is from June to September; rainy and humid weather favors disease occurrence; for potted plants in greenhouses, the disease can occur year-round.

[Control Methods]

(1) Horticultural control: Promptly remove diseased fallen leaves and burn them in a centralized manner. Hydrangea is a perennial plant. Severely diseased plants can be cut off at ground level to regrow new branches. Strengthen cultivation management to promote robust plant growth and enhance disease resistance.

(2) Chemical control: At the early stage of disease, spray 75% chlorothalonil 700x solution, or 70% anthracnose fumei 500x solution, or 70% thiophanate-methyl 1500x solution. Alternatively, spray 60% anthracnose fumei wettable powder 800x solution, or 50% thiram wettable powder 500x solution for control.