Symptoms mainly affect leaves, stems and tubers. Leaves infected with green leaf brown spots at the tips of the leaves or leaves, with a light green halo around the lesions. When the humidity is high, the lesions expand rapidly, appear brown, and produce a circle of white mold, namely cysts and spores. The sac, especially on the back of the leaf, is the most obvious; the lesion becomes brown and dry when dry, crisp and easily cracked, no white mold is observed, and the expansion rate is slowed down. Stem or petiole infected with brown spots. Severe diseased leaves wilted and curled, eventually causing black rot in the whole plant. The tuber was infected with a large spot of primary brown or purple-brown color, slightly sunken, and the skin of the diseased part of the tuber was also brown, and gradually expanded or rotted around.
The pathogen Phytophthora infestans (Mont.) de Bary described P. infestans as a flagellin-inhabiting fungus. The cysts are branched and every other section of the conidia has enlarged nodes. Sporanga lemon-shaped, size 2–3812–23 (μm), with papillary at one end, small handle at the other end, easy to fall off, releasing 5-9 reniform zoospores in water; 2 zoospores with flagellum, After losing the flagellum, it becomes a quiescent spore, germ tube sprouts, and a penetrating nail penetrates into the host. Mycelial growth was suitable for 20-23°C, sporangium formed suitable temperature 19-22°C, 10-13°C formed zoospore, the temperature was higher than 24°C, sporangium germinated more directly, and the relative humidity of sporangium formation was higher than 97°C. %, germination and infestation must have water droplets.
Transmission routes and pathogenic conditions The pathogens mainly overwinter in mycelium with mycelium. Seeds with potato chips are sown that they will die if they do not germinate or sprout after germination. Some of them become central diseased plants after they are unearthed. The diseased part produces sporangia and then re-infects them by air flow to form the onset center, resulting in the disease from spot to face. Rapidly spread and expand. The sporangia on the diseased leaf can also infiltrate the soil with rainwater or irrigation water to invade the potato, forming diseased potato, and become the main source of infection in the following year. The pathogenic bacteria are warm and cool at night, with high humidity conditions, relative humidity above 95% and 18-22°C, which is conducive to the formation of sporangia, cold (10-13°C, hold for 1-2 hours) and the presence of water droplets. Sporangium germination is conducive to the production of zoospore, warm (24-25 °C, last 5-8 hours) there is a drop of water, conducive to sporangia directly output bud tube. Therefore, in rainy years, the onset of disease is heavy under humid or humid conditions. Planting susceptible varieties, the plants are in the flowering stage, as long as there is about 22 °C during the day, the relative humidity is higher than 95% for more than 8 hours, 10, 13 °C at night, the leaves have high humidity conditions for 11-14 hours. Disease can occur, 10 to 14 days after the onset of disease spread throughout the field or cause a pandemic.
Control methods (1) Selection of disease-resistant varieties The currently promoted disease-resistant varieties are: Hubei Potato No. 1 and No. 2, Bada No. 10, Noodle Zhangshu No. 3, No. 24 Center, I-1085, and Short 88-1 to 99 , Suishu 161-2, Zhengshu 4, Yifang 1, Shengli 1, Jiujin, Deyou 1, Tongshu 8, Kexin 4, Xinyi 4, Umeng 601, Wen Victory 2, Qinghai No. 3. These varieties were less affected in the epidemic year of late blight, and they could be selected locally according to local conditions. (2) Use disease-free seed potatoes; reduce primary infection sources. In the process of autumn harvest pits, winter pits, cellar pits, depots, vernalization, etc., the diseased potatoes must be strictly removed each time, and disease-free seeding areas must be established to survive disease-free seeding. (3) Strengthen cultivation and management, timely sowing, planting of well-drained and well-drained plots, promote robust growth of plants, and enhance disease resistance. (4)Initial spraying began with spraying 72% Kelu or Keshuang Cyanide or Husong CWP or 69% Anke, Manganese Zinc Wettable Powder 900-1000 times, 90% triethylaluminum phosphate wettable powder. 400 times liquid, 58% metalaxyl MnZn wettable powder or 64% antivirus WP 500 times, 60% saponin aluminum phosphorus wettable powder 500 times, 50% A wettable powder 700-800 times Liquid, 72.2% Precise (feroxcarb) 800 times liquid agent, 1:1:200 times Bordeaux mixture, every 7-10 days, continuous control 2-3 times.
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