First, occurrence and damage characteristics
1. The main symptoms of damage are leaves, stems and tubers. Leaf lesions usually start from the middle and lower leaves, with water-soaked green-brown spots at the tips of the leaves or leaves, and a light green halo around the lesions. When the humidity is high, the lesions expand rapidly and appear brown, and produce a circle of white mold. The most obvious is the back of leaves; the spots became brown and dry when dry, crisp and easily cracked, and no white mold was observed, and the expansion speed was 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.
2. Causes of the disease Potato late blight is a devastating epidemic, with infected bacteria as the initial source of infection, which requires a cool, humid climate. In a humid environment, pathogens infect the middle and lower leaves of nearby plants through wind and rain. Under appropriate conditions, the bacteria multiply rapidly and multiply to cause infection.
Second, the route of transmission and the incidence of pathogens mainly in mycelium overwintering in the tuber. Seeds of diseased potato are sown that they will die if they do not germinate or germinate. Some of them become central diseased plants after they are unearthed. The diseased part produces sporangia and then re-infects through the air flow to form an onset center, causing the disease to occur from spot to face. Rapidly spread and expand. The pathogenic sporangia can also infiltrate the soil with rainwater or water infiltration and produce diseased potato, which becomes the main source of infection in the following year. The pathogenic bacteria is warm and humid at night, the relative humidity is above 95%, and the condition of 18～22°C is conducive to the formation of sporangia. It is cool (10～13°C, keeping for 1-2 hours) and there are water droplets. It is favorable for the spore sacs to produce zoospores, warm (24～25°C, last 5-8 hours), and there are water droplets, which is conducive to the direct output of germ tube from sporangia. 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, nighttime at 10 ~ 13 °C, the leaves have high humidity conditions for 11 to 14 hours of water droplets. Disease can occur, 10 to 14 days after the onset of disease spread throughout the field or cause a pandemic.
Third, prevention and control technology
1. Agricultural prevention and control is mainly reflected in the cultivation and management, first, the selection of excellent disease-resistant varieties, such as the Atlantic, yam 6 and 7, Zhuangshu 3 and other varieties. The second is to change the rotation. Reasonable crop rotation can reduce the incidence of late blight, and crop rotation can be adopted between potatoes and corn, wheat, vegetables, etc.; third, strengthen cultivation and management, suitable for early sowing, choose loose soil and well-drained fields for planting, promote plant Robust growth, enhanced resistance to disease, early eradication of weeds in the field, emphasis on agrochemical fertilizers, avoidance of partial application of nitrogenous fertilizers or nitrogen fertilizers as top dressings, and timely removal of central diseased plants; fourth, rational close planting to increase ventilation and light conditions in the field, timely Excluding the water after the rain; the fifth is to harvest in time, so that the autumn income pit, winter pit search pit; six is ​​a strict cut potato block, do not broadcast with diseased potato block.
2. Chemical control Chemical prevention should prevent early prevention, seize the appropriate period of control, and use high-efficiency, low-toxic, low-residue pesticides. Seedling period with 75% chlorothalonil Wp600 ~ 800 times liquid spray all fields, the onset period with 64% antivirus 矾wp400 ~ 500 times liquid spray, each mu of liquid can not exceed 50 kg, interval 7 ~ 10 days, even Spray 2 or 3 times to achieve the desired control effect. Also can use 25% metalaxyl wp1000 ~ 1500 times liquid spray 1 or 2 times.
1. The main symptoms of damage are leaves, stems and tubers. Leaf lesions usually start from the middle and lower leaves, with water-soaked green-brown spots at the tips of the leaves or leaves, and a light green halo around the lesions. When the humidity is high, the lesions expand rapidly and appear brown, and produce a circle of white mold. The most obvious is the back of leaves; the spots became brown and dry when dry, crisp and easily cracked, and no white mold was observed, and the expansion speed was 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.
2. Causes of the disease Potato late blight is a devastating epidemic, with infected bacteria as the initial source of infection, which requires a cool, humid climate. In a humid environment, pathogens infect the middle and lower leaves of nearby plants through wind and rain. Under appropriate conditions, the bacteria multiply rapidly and multiply to cause infection.
Second, the route of transmission and the incidence of pathogens mainly in mycelium overwintering in the tuber. Seeds of diseased potato are sown that they will die if they do not germinate or germinate. Some of them become central diseased plants after they are unearthed. The diseased part produces sporangia and then re-infects through the air flow to form an onset center, causing the disease to occur from spot to face. Rapidly spread and expand. The pathogenic sporangia can also infiltrate the soil with rainwater or water infiltration and produce diseased potato, which becomes the main source of infection in the following year. The pathogenic bacteria is warm and humid at night, the relative humidity is above 95%, and the condition of 18～22°C is conducive to the formation of sporangia. It is cool (10～13°C, keeping for 1-2 hours) and there are water droplets. It is favorable for the spore sacs to produce zoospores, warm (24～25°C, last 5-8 hours), and there are water droplets, which is conducive to the direct output of germ tube from sporangia. 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, nighttime at 10 ~ 13 °C, the leaves have high humidity conditions for 11 to 14 hours of water droplets. Disease can occur, 10 to 14 days after the onset of disease spread throughout the field or cause a pandemic.
Third, prevention and control technology
1. Agricultural prevention and control is mainly reflected in the cultivation and management, first, the selection of excellent disease-resistant varieties, such as the Atlantic, yam 6 and 7, Zhuangshu 3 and other varieties. The second is to change the rotation. Reasonable crop rotation can reduce the incidence of late blight, and crop rotation can be adopted between potatoes and corn, wheat, vegetables, etc.; third, strengthen cultivation and management, suitable for early sowing, choose loose soil and well-drained fields for planting, promote plant Robust growth, enhanced resistance to disease, early eradication of weeds in the field, emphasis on agrochemical fertilizers, avoidance of partial application of nitrogenous fertilizers or nitrogen fertilizers as top dressings, and timely removal of central diseased plants; fourth, rational close planting to increase ventilation and light conditions in the field, timely Excluding the water after the rain; the fifth is to harvest in time, so that the autumn income pit, winter pit search pit; six is ​​a strict cut potato block, do not broadcast with diseased potato block.
2. Chemical control Chemical prevention should prevent early prevention, seize the appropriate period of control, and use high-efficiency, low-toxic, low-residue pesticides. Seedling period with 75% chlorothalonil Wp600 ~ 800 times liquid spray all fields, the onset period with 64% antivirus 矾wp400 ~ 500 times liquid spray, each mu of liquid can not exceed 50 kg, interval 7 ~ 10 days, even Spray 2 or 3 times to achieve the desired control effect. Also can use 25% metalaxyl wp1000 ~ 1500 times liquid spray 1 or 2 times.
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