1 Characteristics and hazards of corn rough disease The corn plants infected with MRDV are short and stiff, and the leaves are dark green. The internodes are short and the top leaves are clustered like Clivia. The leaf veins of the leaf back, leaf sheath and eucalyptus leaves have waxy white strip-like protrusions of various thicknesses, which have obvious roughness. The plants are severely dwarfed, the tassels are degenerated, and the ears are deformed. In severe cases, they are not strong.
Since 1993, the occurrence of corn rough disease (MRDV) has increased significantly, causing great losses to the city's corn production. When it occurred in 1996, the rate of diseased plants in general ward was 40%, with an average reduction of 10% to 30%. How to control the damage of corn virus disease, especially corn rough disease (MRDV) has become a very practical issue. Therefore, in recent years, we conducted a systematic investigation on corn rough disease. The study found that 85.16% of the corn plants in the diseased plants were basically produced or discontinued, and the plant height was only 1/2 of that of the healthy plants, and there was no ear or ear without grain; 98.44% of the plants had a loss rate of grain weight. above 50.
2 Comprehensive control method for corn rough disease In the prevention and control of corn rough disease, it is necessary to adhere to the comprehensive prevention and control policy focusing on agricultural control and chemical prevention, the core of which is to control the source of poison, reduce the source of insects, and avoid the harm.
2.1 Strengthening monitoring and forecasting In the disease-prone areas, we will focus on the regularity and regular investigation of the rate and severity of crude disease and disease in wheat, field weeds and corn, and investigate the density and toxicity rate of Laodelphax striatellus. Before the end of autumn and late spring and corn planting, according to the wintering base and poisoning rate of the gray planthopper, the disease plant rate of wheat and weeds, combined with the corn planting mode, timely and accurate forecasting and forecasting of the occurrence trend of corn rough disease Prevention and treatment.
2.2 Selection of resistant varieties Although there is a lack of disease-resistant varieties in the main varieties used in corn production, there are still some differences in the degree of disease among varieties. Therefore, according to local conditions, the varieties with relatively good resistance should be selected, and at the same time, reasonable layout should be paid attention to avoid large-scale planting of single resistant varieties. In Qufu City, the maize hybrids Ludan 50 and Luyuandan 14 are better resistant to rough disease.
2.3 Adjusting the sowing date According to the law of occurrence of corn rough disease, in the recurrence area of ​​disease, the sowing date should be adjusted so that the corn is most sensitive to the disease during the growth period to avoid the emergence period of the gray planthopper and reduce the incidence rate. The corn planting mode in our city mainly includes three types of wheat, corn, corn and late corn. Among them, the most serious disease is wheat, followed by corn, and corn for later. Spring sowing corn should be planted before the middle of April; summer sowing corn should be concentrated from the end of May to the beginning of June.
2.4 Clearing weeds Roadside and field weeds are not only the provenance base for farmland weeds in the coming year, but also the overwintering summer host of the corn-frozen disease-transmitting mediator. Removal of weeds can alleviate the damage of corn rough disease to a certain extent.
2.5 Strengthen field management Combine the seedlings, remove the diseased plants in the field, concentrate on deep burial or burning, and reduce the source of infection of rough disease. Rational fertilization, watering, strengthen field management, promote corn growth, shorten the period of susceptibility, reduce the chance of drug transmission, and enhance the resistance of maize to disease resistance.
2.6 Chemical control First, the pesticide is seeded. Coating and seed dressing of corn seeds with a systemic insecticide can effectively control the gray planthopper in the seedling stage and reduce the spread of rough disease. The second is to spray drugs to kill insects. Before and after corn sowing and seedling stage, spraying insecticides on corn fields and nearby weeds to control Laodelphax striatellus has a certain effect on alleviating the damage of rough disease, and can achieve the effect of pest control.
Valves are found in virtually every industrial process, including water and sewage processing, mining, power generation, processing of oil, gas and petroleum, food manufacturing, chemical and plastic manufacturing and many other fields.
People in developed nations use valves in their daily lives, including plumbing valves, such as taps for tap water, gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, and poppet valves in car engines.
In nature there are valves, for example one-way valves in veins controlling the blood circulation, and heart valves controlling the flow of blood in the chambers of the heart and maintaining the correct pumping action.
Valves may be operated manually, either by a handle, lever, pedal or wheel. Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.
More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements.
Stop Valves, Ball Cock, Angle Valves, Gate Valves, Check Valves
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