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Occurrence and Control Techniques of Powdery Mildew in Sheltered Greenhouse
Powdery mildew is the main disease of Toona sinensis. It has become more and more common in recent years. It has caused serious threat to the production of Toona sinensis, and the yield loss is as high as 70%. The occurrence in the south is more common, the general disease rate is 30% to 50%, and the diseased leaves reach 50% or more in severe cases, which seriously affects the crown development and tree vigor, reduces the yield and quality of axillary buds, and the control of chemical agents is easy to produce drug resistance. Therefore, it is necessary to adopt scientific and rational use of chemical agents to reduce the risk of pathogens based on the principle of giving priority to agricultural control and supplemented by chemical control. 1 Pathogens and hazards The bacteria is a parasite that can only live on a living body. In addition to harming the melon vegetables, it can also harm legumes and a variety of herbs and ornamentals. Powdery mildew mainly damages leaves and sometimes invades shoots. White powder was formed on the surface of leaves, leaves, and twigs, and later on the white powder layer, there were small particles, which were initially yellow, and gradually turned yellow-brown to black-brown, ie, closed cysts. The lesions on the leaves were much less obvious, with yellow-white patches, and curls and coke when severe; the twigs were distorted after being infected, and finally died. 2 Onset conditions The prevalence of the disease in the greenhouse is 16 to 24°C. The range of adaptation to humidity is wide, when the air humidity is between 45% and 75%, the incidence is fast. When it exceeds 95%, it significantly inhibits the development of the disease. Generally, the disease will be mild in a year with less rainfall. The disease develops rapidly when it encounters even cloudy days and hot weather. In the case of weak or prolonged plant growth, it is also susceptible to disease. 3 The onset of pathogenic bacteria overwintered on diseased leaves and diseased branches, and on the second year of spring, the pathogens spread by wind and rain. The bacteria invade the leaves from the stomata and produce a large number of white powdery spores on the back of the leaves that spread the disease. When the conditions are appropriate, the disease occurrence period is very short, and infection can be repeated several times in one year. After the onset, the condition is generally heavier, and if it is not controlled in time, it is difficult to control. Therefore, it is necessary to cooperate with the prevention and treatment of drugs on the basis of prevention. 4 comprehensive prevention and control 4.1 to strengthen the cultivation and management should pay attention to nurturing strong seedlings, a reasonable dense planting, timely pruning and leafing, improve ventilation and light conditions, so that plants grow robustly and improve disease resistance. 4.2 Clean up the Shed Room In time, clean up the diseased branches and diseased leaves and concentrate on stacking or burning. Don't throw it away to prevent the spores of the disease bacteria from flying in the shed. 4.3 Appropriate base fertilizer must be applied with P and K fertilizers, and excessive use of N fertilizer should be avoided during growth. Timely watering and topdressing enhance plant growth and disease resistance. 4.4 Smoke Technology Powdery mildew at the beginning of the disease, every 50 square meters with sulfur 120g, sawdust 500g mix, split several places, the evening began fumigation 1 night, the next morning open air ventilation, or smoked with 45% chlorothalonil The agent is fumigated at 3.75kg per hectare. 4.5 Ecological Control Shelter Shelters shall be strengthened for ventilation management to control the development and infestation of pathogens. In the sunny morning, it is necessary to prevent wind, so that the temperature of the shed quickly rises. The shed temperature rises to 33°C and then the top wind is released. The high temperatures above 31°C can slow down the spore germination rate, delay sporulation, and reduce sporulation. When the temperature of the greenhouse fell below 25°C, windbreaks were continued at noon, keeping the temperature in the afternoon at 20-25°C. When the temperature of the shed fell to 20°C, the vents were closed to reduce the temperature of the shed at night, and the temperature of the shed at night was maintained at 15-17°C. Open vents for ventilation on a cloudy day. 4.6 Chemical control Chemical control of Toona sinensis before germination or early onset. 40% of Fuxing Star Emulsion 8000 to 10000 times liquid or 30% of Perfumed WP 5000 times, 40% of polysulfide suspension 600 times, 30% of Emulsion 3000 times, 6% of Lebiable WP 4000 times liquid, 2% agricultural anti-120, Wuycin 200 times, evenly sprayed on the leaves. When spraying, pay attention to the middle and lower old leaves and the back of the leaves. In the initial stage of disease, spraying once every 7-10 days for 2 or 3 consecutive times can achieve better control effect. Author: Department of Biochemistry, Xingtai University