Symptoms The disease is a devastating disease in the production of green beans in China and Asia. China's Anhui, Henan, Hebei, Shaanxi and other provinces suffer from heavy disease, and suffer heavy damage during the flowering period. At the onset of the disease, the water spots on the leaves were spotted with brownish brown spots, which expanded to form reddish-brown to reddish-brown edges and light gray to light brown near-circular lesions. When the humidity is high, the gray mold layer is densely stained on the lesions, that is, the conidiophores and conidia of pathogenic bacteria. When the condition is serious, the lesions fuse into pieces and soon dry up. Lighter production cuts by 20% to 50%, and serious by 90%.
The pathogen Cercospora canescens Ell. et Mart. is called gray-spraying spores and belongs to the fungus Deinophyta spp. Conidiophore strigose, erect, brown, with 3-8 septa, marked scarring, size 20-1953-6.5 (μm); conidia whip, colorless, with 7-12 membranes, base cut Shape, tip slightly pointed, straight or slightly curved, size 30-3002.5-5 (μm). The bacterium cultured by the strain of PDA can produce a large number of conidia on the sorghum rice medium, and the quantity is closely related to the temperature. The highest sporulation rate is observed at 28° C. for 12 days with 12-hour ultraviolet irradiation and 12-hour dark alternate culture. 24 hours 100% germination.
The transmission route and the disease condition were wintered by the mycelium and conidia in the seed or diseased body, becoming the source of infestation at the beginning of the year. Damaged leaves in the growing season, and they spread rapidly before and after flowering, spreading through wind and rain. Under hot and humid conditions, the conidia are re-infected several times, and a large number of pathogenic bacteria are accumulated, which are prevalent in the case of suitable conditions. High temperature and high humidity are conducive to the occurrence and prevalence of the disease, especially in the rainy autumn, continuous cropping or off-season cultivation.
Control methods (1) Leaf spot resistant varieties such as Qindou 4th, Qindou 6th, Zhonglu 1st, and Luyin 1st were used. The disease-free strain was selected for seeding and soaked in warm water at 45°C for 10 minutes before sowing. (2) After the harvested crops are harvested, deep plowing will be carried out and conditions will be implemented for rotation. (3) In the early stage of onset, spray 50% polymorpha (carbendazim plus dietex), wettable powder 1000 to 1500 times or 75% chlorothalonil wettable powder 600 times, 12% green copper emulsion 600 times , 80% M-45 wettable powder 600 times, 47% Garnett's wettable powder 800 times, 50% mixed sulfur suspension 500-600 times, 30% basic copper sulfate suspension 400 times 1:1:200 times Bordeaux mixture, once every 7-10 days, continuous control 2-3 times.
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