How to Achieve Good Control of Potato Late Blight
Potato (scientific name: Solanum tuberosum) belongs to the Solanaceae family and is a perennial herbaceous plant; its tubers are edible and it is the world's third most important food crop, after wheat and corn. Potato is also known as earth egg, potato, foreign yam, etc., and is the tuber of a Solanaceae plant. Together with wheat, corn, rice and sorghum, it is known as one of the world's five major crops. Potato originated in the Andean region of South America, and the earliest history of artificial cultivation can be traced back to about 8000 to 5000 BC in southern Peru. The main potato-producing countries include China, Russia, India, Ukraine, the United States, etc. China is the country with the largest total potato production in the world. In 2015, China will launch a strategy to make potato a staple food, promoting the processing of potato into staple foods such as steamed buns, noodles and rice noodles; potato will become another staple food besides rice, wheat and corn.
What is potato late blight?
Potato late blight has occurred to varying degrees over the years, seriously affecting the improvement of potato quality, yield and economic benefits. Therefore, the control of potato late blight is extremely important. Potato late blight, also called blight, is a widespread and serious epidemic disease. It occurs in all areas where potatoes are planted. When late blight is epidemic, field yield losses of susceptible varieties can reach 20% to 50%, and storage losses range from 5% to 10% in mild cases and more than 30% in severe cases. Late blight not only harms potatoes, but can also cause damage to tomatoes, peppers, eggplants, etc.
Symptoms of potato late blight
Potato plant leaves, petioles, stems and tubers can all be infected and damaged. In the early stage of leaf disease, dark green water-soaked spots appear at the leaf tip or leaf edge. When the weather is humid, the lesions expand rapidly, and a ring of sparse white mold grows at the edge, especially obvious on the underside of the leaves. In severe cases, the lesions extend to the main vein and petiole, causing the leaves to wilt and droop. When the climate is dry, the lesions dry up and turn brown. When the stem is damaged, slightly sunken streaks initially appear, and in humid weather white mold also forms on the surface. When tubers are damaged, light brown or grayish-purple irregular lesions form, slightly sunken, and the flesh underneath turns brown. When the soil is dry, the diseased part becomes hard and shrinks; when moist, white mold can also grow.
Potato late blight mainly damages leaves, stems and tubers. After onset, the area and number of leaf lesions increase rapidly, causing plants and even entire fields of potatoes to die early in patches, and causing tuber rot, seriously affecting yield. This year, the autumn potato planting area in our county is large and the growth is generally good. Combined with the reality that Shizong has entered autumn with continuous rain, low temperature and high humidity, and large temperature differences between day and night, potato late blight is prone to occur.
Control methods for potato late blight
1. Breeding and promoting disease-resistant varieties: Selecting disease-resistant varieties is the most economical and effective way to control late blight. Different potato varieties differ greatly in their resistance to late blight. Because the potato late blight pathogen is prone to mutation, vertical resistance varieties easily lose their disease resistance after several years of cultivation, so varieties with polygenic resistance or horizontal resistance should be selected.
2. Establish disease-free seed fields and eliminate the primary infection source: Because diseased seed potatoes are the only primary infection source, establishing disease-free seed fields can greatly reduce the primary infection source, thereby effectively preventing the occurrence of late blight. Stricter control measures should be taken in seed fields. Where conditions permit, seed fields should be more than 2.5 km away from main fields to reduce the chance of pathogen transmission. In addition, selecting disease-free seed potatoes can also reduce the primary infection source, and soaking seeds with chemicals can kill pathogens inside the seed potatoes, delay the occurrence of late blight by 20 days, and reduce the disease index by about 50%. For 100 kg of sprouted pieces, use 100 g of 25% metalaxyl, add a small amount of water, and dip or spray.
3. Strengthen field management: 1): Prepare the land and choose high, well-drained terrain for planting; adopt measures such as cultivating and hilling soil, removing tobacco roots, and opening ditches for drainage; increase potassium fertilizer to improve disease resistance. 2): Carefully select seed potatoes before sowing and eliminate infected tubers, which can reduce the number of central diseased plants in the field. Hilling soil in the late growth stage of potatoes can reduce the chance of zoosporangia infecting tubers. In years when the disease is epidemic, appropriately cut the vines earlier and harvest 2 weeks later, which can avoid contact between tubers and diseased plants and reduce the tuber infection rate.
4. Chemical control: In the early stage of late blight occurrence, promptly detect and remove diseased plants, and spray chemical agents on plants within 30—50 m around the central diseased plants. Afterward, spray once every 7-10 days as the situation requires, generally spraying 2-3 times, with good control effects. Drugs can be selected from 58% metalaxyl-mancozeb, 64% oxadixyl, Daconil M-45, 72% DuPont Curzate, 69% dimethomorph-mancozeb, etc. In order to reduce the development of pesticide resistance, it is best to alternate the use of multiple agents.
In short, potato late blight is a devastating disease with serious harm. The control of potato late blight in our county should be carried out in accordance with the policy of “prevention first, comprehensive control”. Only by taking agricultural control as the foundation, chemical control as a supplement, and comprehensively applying multiple control measures can good control results be achieved.