Wang Yiming from Hefei, Anhui Province, came to the telephone and said that recently, his 4 mu mulching of potato on the mulching film had brown round spots on the lower leaves of the plants, resulting in yellow leaves and no lesions on the upper leaves. The rate of diseased plants reached 30%. He asked what diseases the potato had and how it was prevented. According to the preliminary diagnosis of Prof. Wang Yuanchao, Department of Plant Diseases, Plant Protection College, Nanjing Agricultural University, brown round spots on the lower leaves of the potato are likely to have acquired early blight. It is understood that potato early blight occurs throughout the country and mainly damages the leaves. When the disease is serious, it will harm the tubers. Most of the plants began to get infected from the lower leaves of the plant. In the beginning of the disease, water-stained spots appeared on the leaves. Afterwards, they developed into brownish-shaped necrotic spots with concentric ring patterns, and there was a narrow chlorotic halo around the lesion. When the humidity is high, black mold layer (spore of pathogenic spores and conidia) is produced on the lesion. When the onset is severe, the leaves dry out and the field is yellow. Tuber was infected, and the surface was dark brown with slightly sunken round or near-circular lesions. The edges were distinct and the skin was light brown sponge-like dry rot. The pathogen of the disease is Alternaria alternata, which can harm tomatoes, peppers and other vegetables in greenhouses and greenhouses. The pathogenic bacteria overwintered on contaminated and diseased tubers with conidial or hyphae, and the onset of germination occurred the next year when seed germination began. When the conditions are appropriate, conidia are produced on the germs and reinfested by wind and rain. Conidial germination temperature is 26-30 °C, when the leaf surface condensation or water droplets germinate and invade quickly. In the growing period of potato, even continuous rainy weather or humidity is higher than 70%, and the incidence is serious or even popular. Therefore, high-temperature and high-humidity environment are the main factors that cause potato early blight. Recent rainy days and high humidity in the field are conducive to the occurrence of early blight. There are no potato varieties with high resistance to early blight in production, but there are differences in disease resistance among varieties. Generally early-maturing varieties are susceptible to disease, and late-maturing varieties are more resistant to disease. Plants have different disease resistance at different growth stages, and have strong disease resistance from the seedling stage to the bud stage. After the flowering stage, the disease resistance is weakened, and the resistance is weakest after flowering stage. After the early blight of potato, it can be sprayed with 80% mancozeb wettable powder 600-800 times, or 50% isoprenil wettable powder 1000-1200 times, or 77% copper hydroxide wettable powder 500 times. Liquid, or 75% chlorothalonil WP 600 times, once every 7-10 days, continuous control 2-3 times. In addition, potato varieties resistant to early blight are selected; formula fertilization, appropriate application of potash fertilizer, timely spraying of foliar fertilizer, reasonable watering, timely draining and guttering drainage after rain, can reduce the incidence to a certain extent.
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