Potato late blight is a devastating disease. All areas where potato is grown occur, and the degree of loss depends on climatic conditions. The rainy weather this summer is particularly suitable for the occurrence and epidemic of its disease, causing the potato to die in advance, and the reduction of production can be as high as 20% to 40%. The vegetable farmers should do a good job in prevention and control.
First, symptom recognition
Late blight can harm leaves, petioles, stems and tubers (symptoms are shown in the picture). On the leaves, water-stained chlorotic spots begin to appear from the tips of the leaves or leaves. When the humidity of the air is high, the lesions rapidly expand and even extend to the entire leaves, and can invade the petiole and stem along the leaf veins to form brown streaks. There is no clear boundary between lesions and the Ministry of Health, a white mold layer grows on the edge of the dark brown lesions, the back of the leaves is more obvious. When the onset is severe, the leaves are wilted and the whole plant becomes dark and rot. When the weather is dry, the spots are dry and brown, and there is no white mold layer on the back of the leaves. The diseased leaves are brittle and easily broken, and the disease spreads slowly. The stalk suffers a brown stripe of varying lengths after being victimized, and a white mold layer can also grow on the stem stripe under humid conditions. When the potato block is victimized, small irregular spots of light brown are formed, which are slightly sunken. The potato under the spot becomes brown and necrotic, and finally the diseased potato rots. Late blight also causes the potatoes to rot during storage.
Second, the law of occurrence
Late blight is endemic in rainy years. Poorly populated plots with low-lying drainage have a heavy onset, and the incidence of flat land is heavier than that of ridges. Over dense planting or tall plants can increase the humidity in the microclimate, which is conducive to disease. Partial application of nitrogen fertilizer causes plants to grow long, or the soil is thin and oxygen-deficient or sticky soil makes the plant grow weak, which is conducive to disease. The application of potash fertilizer can increase the disease resistance of plants and reduce the occurrence of diseases. Different varieties of potato have very different resistance to late blight. Generally, the leaves are smooth and broad, and the leaves are yellow-green, and the pod-type varieties are susceptible to disease. The erect varieties with small leaves, many hairs, thick leaves and dark greens are more resistant to disease. Varieties with a large number of stomata on the leaf surface are also susceptible to disease. Potatoes have different resistance to late blight at different growth stages. Generally, seedlings have strong disease resistance, and they are most susceptible to disease before and after flowering. The affected parts of the leaves also affected the disease. The parietal leaves were the most resistant to disease, followed by the middle, and the bottom leaves were most susceptible to disease.
Third, control methods
1. Use resistant varieties. The resistance of different varieties of potato to late blight is very different because the potato late blight bacteria are prone to variability and vertical disease resistance (cultivates against certain races of a pathogen but not other races) is planted for several years. After that, it is easy to lose its disease resistance, so species with a level of disease resistance (disease resistance is generally consistent with all races of the pathogen) should be selected.
2. Establish a disease-free location and use disease-free seed potatoes. Disease-free fields should be separated from Daejeon by more than 200 meters in order to reduce the chance of transmission and infestation of pathogens, and various control measures must be strictly implemented. In disease-free plots, disease-free plants can be selected.
Seed treatment. Soaking with a systemic fungicide, such as 50% carbendazim 500 times soaking, can also be used 200 times formalin solution soaking. Then piled up and covered tightly, boring for 2 hours, then spread out to dry.
4. To strengthen the cultivation and management. Select seed potatoes before sowing and eliminate the contaminated tubers can reduce the number of diseased plants in the field. In the late growth period of potato cultivation, the chance of zoosporangium invading the potato can be reduced. In the epidemic year of disease, cutting vines earlier and harvesting the tubers two weeks later can avoid the chance of contact between tubers and diseased plants, and reduce the rate of tuber inoculation.
5. Chemical control. When the central diseased plant appeared in the field, the central diseased plant was immediately cleared, and 1% to 2% copper sulfate solution was sprayed. The spray was sprayed every 7 days and sprayed continuously for 2 to 3 times.
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