Occurrence and Control of vegetable Seedling Diseases

Seedling cultivation is a very important link in vegetable cultivation,"good half harvest seedlings" is the best summary of cultivating strong seedlings. With the continuous development of vegetable facility cultivation and the continuous expansion of vegetable cultivation area in southern "natural greenhouse", the seedling mode and season are also constantly changing, and disease prevention and control has become one of the key technologies in the process of cultivating strong seedlings. 1. Occurrence and damage characteristics of vegetable seedling diseases: At present, the seedling cultivation of vegetables such as solanaceous fruits, melons and beans in winter and spring is mainly to provide strong seedlings for early cultivation in spring in protected areas and spring cultivation in open fields; the seedling cultivation of vegetables such as solanaceous fruits, melons, cruciferae and beans in summer and autumn is to provide strong seedlings for delayed cultivation in autumn in protected areas, autumn cultivation in open fields and vegetable cultivation in south and north transportation. In winter and spring, damping-off, blight, gray mold, anthracnose and root rot were the main diseases in seedling stage, and in summer and autumn, virus disease, anthracnose, sclerotium and heat damage were the main diseases in seedling stage. 1.1 Damping-off disease: mainly harmful to eggplant, melon, celery, lettuce, cabbage, onion and other vegetable seedlings, is a kind of disease that often occurs during winter to early spring seedling, occurs more before the seedling is not unearthed to the true leaf has not fully unfolded, at this time the nutrients in the cotyledons of seedlings have been exhausted, the new roots have not been firmly rooted, the young stems have not been cork, and the seedling disease resistance is the weakest. During this period in case of cold, low temperature and even rainy weather or sowing too dense, soil moisture is larger, not conducive to seedling growth, it is easy to cause damping-off disease. 1.2 The host range is very wide, according to incomplete statistics up to more than 160 kinds, including solanaceous fruits, melons, beans, cruciferous, celery, lettuce and other vegetables, mostly in the seedling just unearthed to the time before planting, especially in the middle and late seedling disease is more common. More rainy weather, higher seedling bed humidity easily lead to excessive seedling growth, aggravated the occurrence and spread of blight. 1.3 Gray mold: In recent years, it is a rapid and serious vegetable seedling disease in the process of seedling cultivation in winter and spring, mainly damaging vegetables such as solanaceous fruits, lettuce, celery and beans. It occurs more in the middle and late stages of seedling growth, and often develops from point to piece in seedling bed. When the temperature is low and the humidity is high, it is easy to cause death of seedlings in pieces, and even the seedlings in the whole shed are destroyed. 1.4 Anthracnose: In recent years, pepper, sweet pepper, watermelon, melon, white gourd, kidney bean and other vegetables seedlings occur more seriously, from cotyledon growth to planting before can occur, temperature and humidity appropriate, seedling growth point is killed, seedlings are easy to die. Due to the variety of anthracnose bacteria that harm vegetables and the wide adaptability of pathogenic bacteria to temperature, many kinds of vegetable seedlings are prone to anthracnose in winter, spring and summer, especially in summer and autumn under the climatic conditions of high temperature and rain, it is more likely to produce a large area of water-stained disease spots on the leaves and acute defoliation from bottom to top, which is harmful to seedlings. 1.5 Retting roots: almost all winter and spring vegetable seedlings can produce retting roots, seedlings do not grow new roots for a long time after they are unearthed, the young roots are rusty brown and gradually rot; the growth of stems and leaves is inhibited, the leaves gradually turn yellow, and new leaves are not produced. The sick seedlings are easily pulled out from the soil. In severe cases, the diseased plants wither and die. Seedling retting root is a physiological disease, mainly due to rain and snow in winter and spring or rainy weather more, serious lack of light, seedbed soil temperature is low, humidity, seedling respiration blocked, water absorption capacity reduced caused. 1.6 Sclerotinia sclerotiorum: It is an important disease that is easy to occur in many kinds of vegetable seedlings in summer and autumn, especially the seedlings of spicy (sweet) pepper, eggplant, beans and melons in the vegetable base transported from south to north. 1.7 Viruses: Viruses almost occur in summer and autumn vegetable seedlings. Due to the high virus-carrying rate of beans, melons and other vegetable seeds, virus diseases appear as soon as they are unearthed. In addition, some insects such as aphids are easy to spread viruses. In addition, some viruses are easy to spread through agricultural operations. Therefore, the incidence of virus diseases in summer and autumn vegetable seedlings is very high. 1.8 Heat damage: It is a physiological disease often encountered by vegetable seedlings in summer and autumn. It often occurs on seedlings cultivated by shelter facilities. It is mainly due to the fact that the film is not removed in time after rain, and the temperature in the shed exceeds 40℃, sometimes reaching more than 50℃, resulting in seedling leaves or growth points burning, which is difficult to recover in a short time. 2. Integrated control techniques for vegetable seedling diseases: Only by taking comprehensive disease control measures can the occurrence and damage of seedling diseases be truly controlled. At present, the following comprehensive measures are usually taken. 2.1 Selection of seed beds. Seedbed land should be selected high terrain, smooth drainage, loose fertile soil disease-free plots. Winter and spring seedling bed best shelter from the sun, summer and autumn Nancai North base seedling bed best choose easy to ventilate heat dissipation plot. 2.2 Selection of seedbed soil and fertilizer. Bed soil is best selected disease-free new soil, old bed soil or old vegetable garden soil is likely to carry bacteria, usually should be bed soil disinfection, the most common method is currently used per square meter of seedbed application of 50% carbendazim or 50% thiophane methyl wettable powder 5g, to fine soil 5kg evenly mixed, before the application of seedbed first irrigation bottom water, one-time irrigation, water infiltration, take 1/3 fully mixed soil on the ridge surface, after sowing the remaining 2/3 soil cover the seeds, seeds sandwiched in the middle of the soil, The control effect is obvious and the efficacy time is long, but the dosage should be strictly controlled, not too much, otherwise it is easy to cause phytotoxicity. This method has good control effect on seedling damping-off disease and seedling blight. Organic fertilizer for seedbeds is best used after full fermentation at high temperatures, which not only kills pathogens, but also kills eggs and seeds. 2.3 Disinfection of seeds. 1 warm soup soaking: this is the most commonly used method of seed disinfection treatment, eggplant and melon seeds are generally soaked in warm water at 55 ℃ for 10~15min(min), during which they are constantly stirred, until the water temperature drops below 30℃, cucumber is soaked for 2h(h), tomato, pepper and eggplant are soaked for 4h(h), wax gourd is soaked for 0.5 h (h), and the soaking temperature and time should be strictly controlled when soaking in warm water, so as not to affect seed germination. (2) Dry heat treatment of seeds: dry seeds of cucumber, watermelon, melon or tomato were treated with dry heat at 70℃ for 3 days (days), which could kill pathogens on the surface and inside of seeds.③ Seed treated with chemicals: Soaking seeds with 0.1% 60% carbendazim hydrochloride ultramicro powder solution for 50~60min(min), taking them out and washing them clean for germination, is beneficial to seedling emergence and prevention of sclerotinia sclerotiorum and anthracnose at seedling stage; dressing seeds with 0.4% captan can prevent damping-off and seedling blight; soaking seeds of tomato, pepper, sweet pepper and watermelon with 10% trisodium phosphate (Na 3PO 4) aqueous solution for 20~30min(min) and rinsing them with clean water can prevent virus diseases. 2.4 Strengthen seed bed management.① In winter and spring, it is recommended to raise seedlings in electric hotbeds or factory trays, and in summer and autumn, it is recommended to prevent insects, shade and shelter seedlings from rain, so as to minimize the influence of bad weather in the process of seedling raising, and at the same time, it is convenient for scientific management. (2) Anti-freezing and heat preservation measures should be taken for seedling cultivation in winter and spring, and the mulch should be uncovered in due time. The disease resistance of seedlings will be easily reduced if the seedling bed temperature is too high or too low. As long as the seedbed temperature permits, cover should be removed in time to increase light to improve seedling disease resistance.③ In summer and autumn, measures should be taken to prevent insects, cool down and shelter from rain, and three links are indispensable. Seedlings are prone to virus disease if insect control is not timely, and it is difficult to cure seedlings once infected with virus; seedlings grow poorly and are easily burned if cooling measures are not effective; seedlings are easily damaged by strong wind and heavy rain if rain protection measures are not kept up, and seedlings may be washed away by typhoon and rainstorm sometimes. At the same time, it is necessary to pay attention to removing the rainproof film in time after the rain to prevent the seedlings from being burned.④ Strictly control the moisture content of seedbed. The soil humidity and air humidity of seedbed were the key factors of disease occurrence in seedling stage, especially in winter and spring. The seedbed should be watered at 10:00~12:00 in sunny day, and the air should be released at noon after watering. (5) Lowering soil moisture and raising soil temperature are the fundamental measures to reduce the root rot of vegetable seedlings in winter and spring. Intensify seedbed inspection, and remove sporadic diseased plants of virus disease, gray mold, sclerotinia sclerotiorum and blight in time. The purpose of controlling the spread of diseases can also be achieved by reducing bacterial sources. 2.5 Chemical control. At the early stage of disease, spraying 400 times solution of 15% hymexiline aqueous solution, 500 times solution of 40% Dakolin suspension, 500 times solution of 50% thiophanate-methyl wettable powder or 600 times solution of 60% carbendazim hydrochloride ultrafine powder in sunny morning had better control effect on damping-off and anthracnose. Spraying 800 times solution of 58% Radomil WP, 600 times solution of 25% Metalaxyl WP or 500 times solution of 64% Trimethoprim M8 had better control effect on seedling blight. Attention should be paid to spraying the stem base of seedlings. 50% Prochloraz WP 1000 times solution or 30% Nongliling WP 2000 times solution can be used to spray gray mold and sclerotinia sclerotiorum at seedling stage. In case of continuous rainy weather, 10% Sukeling or Nongliling smoke agent or 15% Sukeling-chlorothalonil compound smoke agent can be used 250g per mu of seedling shed (room, room), which is fired at 4~5 points and smoked in a closed night. The control effect on gray mold and sclerotinia is better than spraying. The control effect of 15% Pythium fumigant 250g/mu on damping-off and Rhizoctonia solani was better. Depending on the weather conditions, smoke agent and spray alternate use, conducive to improving the control effect, depending on the disease for 2 to 3 times of continuous application, can control the spread of the disease. The key measure to prevent virus disease is to control aphids in summer and autumn. At present, the better insecticides for aphids control are 90% Wanling soluble powder 2000 times, 10% Chuji suspension 2000 times, 21% Mishashi EC 5000 times, 10% imidacloprid WP 1500 times and 50% aphimicarb WP 1500 times. For mild virus disease seedlings, spraying 500 times solution of 20% virus A wettable powder or 800 times solution of 1.5% Zhibingling emulsion had certain effect.