What are the main diseases of potatoes? How to prevent it?

(1) ring rot usually occurs after flowering. The initial symptoms are yellowing, withering and upward curling of the leaf margin. There is no obvious symptom when the surface symptoms of tuber are slightly damaged. With the development of the disease, the skin turns black or brown, and the bud eyes also change color, but no fungal pus overflows. In severe cases, cracks may appear on the epidermis. In tubers with cross-cutting disease, vascular bundles can be seen to turn yellow or brown. In light cases, only local vascular bundles turn yellow, showing discontinuous punctate discoloration; In the worst case, the whole vascular bundle ring becomes discolored, and pathogenic bacteria invade the parenchyma around the vascular bundle of tuber, which is ring rot. Control methods: select disease-resistant varieties; Rotation with non-solanaceae vegetables for more than 5 years; Establish a disease-free seed field and sow whole potatoes as much as possible; Seed potato treatment: first put the seed potato indoors for 5~6 days, dry it, and constantly remove the rotten potato. Seeds can also be soaked with 50 mg/L copper sulfate solution 10 minute, or with 70% sodium sulfamate soluble powder (0.2% of the seed weight). (2) Potato early blight mainly harms leaves and stems. When the blade is damaged, it produces round or nearly round dark brown spots with concentric wheel lines, with a size of 3~4 mm. When the humidity is high, the black mold layer will be produced on the spots, and when the disease is serious, the leaves will dry up and fall off, which will cause the leaves in the field to be burnt. Tubers are infected with dark brown or dark brown spots, round or nearly round spots, some slightly sunken, with obvious edges, and light brown spongy dry rot under the skin. Prevention and control methods: select early-maturing and disease-resistant varieties and harvest them early; Rotation with non-solanaceae crops for 2~3 years; Choose a field (land) with fertile soil and good drainage for planting, and fully apply base fertilizer; Spraying 7500 times of phytochemicals on leaves can improve the disease resistance of plants. At the beginning of the disease, 600 times of 75% chlorothalonil wettable powder, 500 times of 64% antiviral alum wettable powder or 400 times of 40% captan wettable powder were selected, and the dosage of liquid medicine was 60kg/ mu, and it was sprayed every 7~ 10 day/time for 2~3 times in a row. Be careful not to use drugs for 10~ 15 days before harvesting. (3) Potato late blight mainly occurred on leaves, petioles, stems and tubers. On the blade, it often happens at the tip and edge of the blade. At first, it was a waterlogging spot, which expanded rapidly when the weather was wet. There is no obvious boundary between the diseased part and the healthy part. There is a white and sparse mold ring at the edge of the lesion, and the back of the leaf is more obvious. In severe cases, the lesion extends to the main vein or petiole, causing the leaves to wither and droop, and finally the whole plant becomes dark and wet. When the weather is dry, the lesion is dry and brown, and no mildew wheel is produced. When the potato is susceptible to disease, it forms brown or purple-brown irregular spots and slightly sinks. The potato meat below the diseased spot is a brown necrotic part with different shades, and the diseased potato is often soft rot due to bacterial infection. Potato will get sick in the ground, rot in the ground, and get infected and rot in the ground after entering the cellar. Prevention and control methods: cultivate disease-resistant varieties; Establish disease-free farmland; Rotation with non-solanaceae crops for 2~3 years; Seed potato treatment: 50 g of 72% cymoxanil manganese zinc wettable powder or 50% manganese zinc flumorph wettable powder can be added with 2-3 kg of water, and then evenly sprayed with wine on 150 kg of seed potato block, or evenly mixed with 2-3 kg of fine soil or fine ash of the same chemical agent, and then mixed on 150 kg of seed potato block, and coated with plastic. After the central diseased plant appears, it should be pulled out immediately and sprayed all over the field for prevention and control. The dosage of liquid medicine can be 60 kg/mu, 500-600 times of 25% methomyl wettable powder, 300 times of 40% ethyl aluminum or 800 times of 80% mancozeb dry suspension. Be careful not to use drugs for 10~ 15 days before harvesting. (4) The main manifestation of potato virus disease is that the compound leaves growing from the heart leaves of plants begin to become smaller, which is obviously different from the lower leaves. The newly grown petiole is erect, the leaflets are often deformed and the leaves are rough. There are three main symptoms: ① mosaic type. The distribution of chlorophyll on leaves is uneven, showing mottled mosaic of dark green and light green or yellow-green. In severe cases, the leaves atrophy and the whole plant is dwarfed, sometimes accompanied by transparent veins. ② Necrotic type. Brown necrotic spots can appear on leaves, veins, petioles and branches, and the diseased spots develop and become necrotic zones. In severe cases, the whole leaf dies or withers and falls off. ③ Leaf-rolling type. The leaves turn inward along the main vein or from the edge and become hard and leathery. In severe cases, each leaflet is tubular. Control method: select virus-free seed potato for planting; Early removal of diseased plants; If aphids are found, prevent them in time. At the initial stage of the disease, 700 times of 24% mixed fatty acid-base copper solution, 300 times of polysaccharide solution, 300 times of 4% pyrimidimycin solution, 500 times of 20% morpholine ethyl copper wettable powder, or 500 times of 7.5% mycotoxin morpholine muscle solution can be selected, and it can be sprayed 1 times according to the condition. Be careful not to use drugs for 10~ 15 days before harvesting.