Leaf spot of Impatiens balsamina

[alias] Fengxianhua brown spot. Leaf spot of eight Immortals is one of the common diseases on eight Immortals.

Sichuan, Henan, Guangdong, Taiwan, Jilin, Shanghai, Zhejiang, Hunan and other places.

[symptoms] the disease mainly occurs in leaves. The foliar spot is a light yellowish brown watery spot at first, and then expands into a circle, nearly round, with a diameter of 2 to 5 mm, up to a maximum of about 15 mm. Later, the center is light brown, the edge is dark brown, slightly raised, with inconspicuous wheel lines, and the disease produces small black spots, that is, the conidium of the pathogen. On the seriously susceptible leaves, there are a series of disease spots, which causes the leaves to turn brown and yellow until the plant dies. It occurred from August to September.

[pathogen] the pathogen is fungus, Cercosporafukushiana, belonging to the subphylum Cercospora, Cercospora. Sporangium underdeveloped, conidiophores clustered, light brown, rarely separated or branched, straight or wavy, or geniculate flexion 1-3, size 10-100um × 4-6um. Conidia narrowly clavate. Straight or curved, tapering to the top, truncated at the base, septum many, but not obvious, flat at the base, tip pointed, 30-140um × 3-4.5um.

[incidence regularity] the pathogen overwintered on diseased leaves and soil plant fragments. In the following year, when the environmental conditions were suitable, conidia were produced from the conidia, and the conidia were dispersed by wind and rain. A large number of conidia on the new disease spot spread through air flow, resulting in repeated re-infection. High humidity and heavy rain are conducive to the occurrence and spread of the disease. The disease occurred from August to September and decreased gradually in October. Old leaves are easy to get sick.

[prevention and control methods]

(1) Horticultural control: impatiens likes fertile sandy loam and is not resistant to waterlogging. Therefore, it is appropriate to plant sandy loam to facilitate drainage; potted impatiens should be poured out in time after rain. Diseased leaves and plants should be destroyed at the end of autumn to reduce the source of infection in the coming year.

(2) Seeds were collected from disease-free and robust plants and disinfected with potassium permanganate or zinc benzoate before sowing.

(3) Pharmaceutical prevention: spray prevention with 0.5% Bordeaux solution before onset. Early detection of diseased leaves and timely removal. Spray control at the initial stage of the disease or when the disease is serious, you can choose 50% carbendazim 500x solution, or 75% chlorothalonil 700x solution or 25% carbendazim wettable powder 300,600x solution, or 50% methyl thiophanate 1000-fold solution or 50% carbendazim 800-1000 times liquid. Or 50% carbendazim 600 times. Or spray 40% polysulfide suspension 500 times, 50% mixed sulphur suspension 500 times, 1 200 Bordeaux solution, 77% wettable powder 500 times solution, 50% copper succinate (DT) wettable powder 400 times 500 times, once every 10 days, control 2 times 3 times.