Detailed methods for the prevention and control of cassia leaf spot disease
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Cassia leaf spot disease is a general term for various spot diseases on cassia leaves, such as brown spot disease, leaf blight disease, (T-J) disease, etc., which cause early defoliation, weaken plant growth, affect ornamental value, and reduce cassia yield, causing economic losses.
Symptoms of cassia brown spot disease
Initially, the affected leaves show small chlorotic spots, which gradually expand into nearly circular lesions or irregular lesions due to leaf vein constraints. The lesions are yellowish-brown to gray-brown, surrounded by a yellow halo, with a diameter of 2 to 10mm. In the later stage, black mold-like substances appear on the affected area, which are the conidia and conidiophores of the pathogen. The pathogen of cassia brown spot disease belongs to the Fungi Imperfecti, Hyphomycetes, Moniliales, and Cercospora. The stroma is brown and subcircular; conidiophores are bundled and grow on it, light olive in color, unbranched, rarely septate; conidia are inverted club-shaped, nearly colorless to light olive, straight or slightly curved, measuring 15-58×2.8-3.7μm. The disease occurs from April to October, with older leaves being more severely affected. The mycelium overwinters on the diseased leaves and serves as the primary source of infection in the following year. Under suitable temperature and humidity conditions, conidia are produced in the affected area and spread to healthy leaves with air currents and water droplets, causing infection.
Symptoms of cassia leaf blight disease
The pathogen usually invades from the leaf tip or margin, initially appearing as light brown spots, which gradually expand into circular or irregular large lesions. In severe cases, several lesions merge to form large blighted areas, causing 1/3 to 1/2 of the entire leaf to dry up. The lesions are gray-brown to reddish-brown, with a distinct reddish-brown margin that sometimes curls and cracks. In the later stage, many small black dots, the conidiomata of the pathogen, appear on the affected area. The pathogen of cassia leaf blight disease belongs to the Fungi Imperfecti, Coelomycetes, Sphaeropsidales, and Phyllosticta. The conidiomata are nearly spherical with an opening, measuring 100-150μm in diameter; conidia are oblong to subfusiform, colorless, unicellular, measuring 6.0-9.5×1.8-2.5μm. The pathogen develops at temperatures of 10-33°C, with the optimal temperature being 27°C. The disease commonly occurs from July to November, with the conidiomata overwintering on the diseased leaves and spreading by wind and rain. The disease is severe in high temperature and humidity, poor ventilation, and weak plant growth.
Symptoms of cassia (T-J) disease
Initially, the affected leaves show small chlorotic spots, which gradually expand into circular, semicircular, or oblong lesions. The lesions are light brown to grayish-white, with a reddish-brown ring around the edge. In the later stage, many small black dots, the conidial plates of the pathogen, appear on the affected area, and a light pink mucilaginous spore mass appears when it is wet. The pathogen of cassia (T-J) disease belongs to the Fungi Imperfecti, Coelomycetes, Melanconiales, and (T-J) fungi. The conidial plates are brown or black, measuring 100-300μm in diameter, with several setae on the plate; conidiophores are cylindrical, measuring 12-21×4-51μm; conidia are cylindrical, located under the leaf epidermis, breaking through the epidermis when mature, measuring 11-18×4-6μm. The disease occurs more severely from April to June, with the conidial plates overwintering on the diseased leaves and spreading by wind and rain.
Control methods
1. Reduce infection sources: Diseased leaves of potted cassia should be removed in time, and all diseased leaves should be thoroughly cleaned and incinerated in autumn to reduce or eliminate the primary infection sources; seedlings from severely affected areas should be soaked and disinfected with a potassium permanganate solution (1000 times) before being sold.
2. Garden technical measures: Strengthen cultivation management, avoid soil waterlogging, apply humus fertilizer and potassium fertilizer, plant at a reasonable density, maintain ventilation and light, to improve plant resistance and control the occurrence of the disease.
3. Chemical control: Apply chemicals in the early stage of the disease. For brown spot disease, a Bordeaux mixture (1:2:200), or a 50% benlate solution (1000-1500 times) can be sprayed for control; for leaf blight disease, a 65% zineb solution (500 times) or a 40% carbendazim solution (600-800 times) can be sprayed for control; for (T-J) disease, a 50% thiabendazole solution (800-1000 times) or an 80% (T-J) captan solution (600 times) can be sprayed for control. Chemicals should be alternated and applied continuously for 2-3 times for better results.
The above content is a detailed explanation of the prevention and control methods for cassia leaf spot disease, hoping it will be helpful to green plant enthusiasts!