1 pesticide drifting phytotoxicity Pesticide drift will reduce the efficacy of the drug, pollute the environment, harm sensitive plants, and cause economic losses. Pesticide drift can be divided into two categories: one is the first sexual drift, called the main drift, but also can be divided into two types, the spray width drift, and the first is the long distance drift. The other type is the second sexual drift, including volatile drift. 1.1 Close distance drift The close-range drift is also called the spray width drift. It refers to the pesticide droplets under the action of the wind, and the off-target movement is closer. The ground plant protection machinery sprays the drift distance to generally 9 meters, and the aircraft spray can reach 90-120 meters. It consists of a large diameter droplet, and the air stay is less than 30 seconds. The spray height and the crosswind speed determine the drift distance. Spraying the spray can damage nearby sensitive plants. 1.2 long distance drift The long-distance drift consists of smaller droplets, which are light in weight and far away from drifting distance, which greatly exceeds the distance of the spray. As long as the pesticide is sprayed, some degree of long-distance drift will occur, and the droplets will drift a few kilometers or more downwind. Due to the small droplets, the local meteorological conditions greatly affect the direction and distance of the droplets. The location of the drifting hazard is not directly related to the distance along the wind direction of the application point. The mist droplets may drift or drift away in the air for a considerable distance. Therefore, it is difficult to predict and measure long-distance drift. 1.3 second sexual drift The second sexual drift occurs after the pesticide is sprayed, including pesticide spraying onto the crop. The liquid is dried on the surface of the stems and leaves of the plant, and some pesticides crystallize out, some of which are blown off by the wind and deviate from the target sediment; the soil adsorbs pesticides under the action of strong winds. The pesticide moves away from the target with the soil dust particles; the pesticide enters the plant body and diffuses into the air with the transpiration flow; the pesticide is volatilized into the air. Among them, volatile migration can cause plant phytotoxicity, such as 2,4-butyl butyl ester, which is commonly used, because the vapor pressure is higher, the first drift is 11% to 14%, and the volatile migration is as high as 12% to 19%. Above °C, it begins to volatilize and drift, increasing with increasing temperature. The first drift of 2,4-Dramine salt was only 3% to 4%, and the first drift of the herbicide was 5%. The two pesticides had little volatile migration. Because the volatilization of pesticides is related to its physical and chemical properties, the vapor pressure is higher than the vapor pressure, and the volatiles are more serious. The esters are larger than the salts. Therefore, 2,4-butyl butyl ester can not be used in North China and the South, and the use of the North often causes damage to forest trees, orchards, vegetables and sensitive crops. Northern sinensis, 2,4-butyl butyl ester, drifting harm to Schisandra, prominent phytotoxicity, huge losses. In 2007 and 2008, the large area of ​​Schisandra in Yichun City was harmed by 2,4-D and Eclipta. In the morning foggy weather, 2,4-butyl butyl ester and dysentery vapour floated away from the fog for a long distance, characterized by foggy days drifting a few kilometers along the long distance of the ravine. 2 Analysis of factors affecting pesticide drift 2.1 Spraying liquid droplet size The main factor affecting the first sexual drift of pesticides is the size of the droplets. The droplets with droplet diameters less than 100 microns are likely to cause drift. When the aircraft sprays the droplets vertically down to a height of 3 meters and the wind speed is 1.33 meters per second, the droplet diameter is 400 meters and the drift distance is 3 meters, and the landing time is 2 seconds; the droplet diameter is 240 meters, the drift distance is 6 meters, and the landing time is 5 Second; the diameter of the droplet is 100 micrometers, the drift distance is 23 meters, the landing time is 11 seconds; the droplet diameter is 20 micrometers, the drift distance is 750 meters, and the landing time is 4 minutes. The smaller the droplet, the longer it stays in the air and the higher the probability of drift. The diameter of the droplets below 20 microns is suspended in the air for a long time. The buoyancy of the air can offset the quality of the droplets, and the droplets are difficult to drop, so they can drift longer distances. The aircraft sprays pesticides behind crops, with a flying height of 2 to 4 meters, a safe and effective droplet diameter of 200 to 250 microns, a flying height of 4 to 5 meters, a spray droplet diameter of 250 to 400 microns, and a spray droplet density of the systemic pesticide. 30 to 40 / cm2, contact pesticides 50 to 70 / cm2. Spraying post-emergence herbicides generally use droplets with a diameter of 250 to 400 microns, which can prevent the herbicide from drifting and obtain good herbicidal effects. 2.2 Flight altitude Adjusting the flight height of the aircraft is a simple and easy method. The higher the flight altitude, the more serious the drift. Aircraft spraying herbicides use a lower flying height to reduce drifting phytotoxicity. 2.3 Meteorological conditions Meteorological conditions are important factors affecting drift, and the impact on drift can reach 10% to 30%. Under certain special conditions, meteorological conditions can become the main factor. Local microclimate factors such as wind speed, wind direction, relative humidity, temperature, atmospheric stability and inversion temperature during spraying. The impact of various meteorological conditions on drift depends critically on the number of droplets less than or equal to 100 microns in diameter. If measures are taken to avoid the generation of these small droplets, the impact of meteorological factors is minimal. (1) Wind speed Wind is an important factor affecting drift. Generally, the greater the wind speed and the farther the drift of the droplets, the elimination of droplets with a diameter of less than 100 microns, which can greatly shorten the drift distance of the droplets. Regardless of the size of the droplets, the total amount of drift increases as the wind speed increases. At high wind speeds, the drift of the herbicide spray can harm nearby sensitive crops, and the long-distance drift hazard may be alleviated. It is also worth considering that the average or instantaneous value of wind speed measured by wind speed changes does not reflect changes in wind speed in the field. For example, the gust wind speed can be higher than the average wind speed by several kilometers per hour. If the wind speed exceeds 2.23 meters per second, the normal isolation zone may not be enough, and sensitive crops may be damaged by drift. The wind speed on the plant crown is much higher than the surface wind speed. For example, the forest with a height of 15 meters, the upper wind speed is 2.2 m / s, and the surface wind speed is 0.26 ~ 0.53 m / s. (2) Wind direction For sensitive crops, wind direction is an important factor that can cause drift hazards. First, when designing the field work before the operation, find out the distance and type of sensitive crops in the downwind, and leave the wide separation belt or apply the medicine when the wind direction changes. Or apply the morning, evening or night when the airflow is stable. (3) Relative humidity and temperature Two closely related meteorological factors affect the drift hazard of herbicides. When the droplets fall in the air, the surface moisture evaporates into the air, so that the volume of the droplets decreases, the mass becomes lighter, and the residence time in the air becomes longer, which is farther than the normal drift distance. The rate of evaporation of water in a droplet depends on the ambient air temperature and relative humidity. Assuming no evaporation occurs, the 100 micron diameter droplet drops freely 1.5 meters, takes 5 seconds, at a temperature of 25.5 ° C, relative humidity of 30%, the same 100 micron diameter droplets quickly evaporate, falling 0.75 meters, the droplet diameter is reduced By 46 microns, a 54% reduction, its volume and mass are reduced by 8 times, reduced by 85%, and can be permanently suspended in the air stream. At a temperature of 25.5 ° C and a relative humidity of 70%, the same 100 micron diameter droplet dropped 1.5 meters and fell to the surface to evaporate to a diameter of 46 microns. The loss of water from the droplets can increase the number of small droplets in the droplets. However, almost all the meteorological conditions cause evaporation loss. In the morning and evening, the temperature is low, the relative humidity is high, the evaporation loss is small, and the herbicide is sprayed. the best. Small droplets have a very large surface area. During the descent process, the evaporation rate does not increase. At 50% relative humidity, 25.5°C, the droplets of 20 microns or less evaporate almost immediately; under the same conditions, 200 microns or Larger droplets usually drop to the ground before evaporating. In addition to affecting the evaporation loss of the droplets, the temperature can also affect the drift in other ways, such as the evaporation of the herbicide increases with increasing temperature. Temperature also affects air turbulence, air stability, inversion, etc., which in turn affects drift. (4) Atmospheric stability and temperature Under standard meteorological conditions, for every 300 meters rise, the temperature drops by 3 ° C, that is, every 100 meters rises, the temperature drops by 1 ° C. This is called "normal gas drop" or "temperature gradient", and the atmosphere is unstable due to turbulent air flow and vertical circulation. When the heating flow rises, the small droplets suspended in the near-surface warm current also rise vertically, and are dissipated into the upper air by turbulent flow and vertical circulation. Since the herbicide has been diluted by the atmosphere, the possibility of such drifting hazard Become smaller. If the gas flow is very stable, the normal gas drop or temperature gradient does not exist, the suspended herbicide droplets do not rise and stay in the low air layer, and are concentrated into a high concentration of herbicide air mass. If these drug groups drift away from the target, it will cause toxic damage to sensitive crops. Atmospheric stability is associated with a phenomenon known as "atmospheric inversion" and thereby increases stability. In the presence of inversion, a layer of warm air in the atmosphere breaks the normal vertical temperature gradient, covering the cold air below, and the inversion interface can exist at any height, from a few meters to several hundred meters from the surface. The warm air cover prevents air and suspended herbicide droplets from drifting up. Air circulation is limited to the low air layer, so the herbicide air mass can only move sideways, up to several kilometers, and if it falls, it will fall back to the ground, which may cause dangerous plants to drift. Atmospheric inversion occurs mostly in the morning. If cold air invades from nearby lakes, oceans, rivers, reservoirs, and irrigated paddy fields, it will cause the warm air in the area to rise and form an inversion layer. Inversion is often dissipated at noon. If you are worried about the above two unfavorable spraying conditions, you should apply the medicine after 6 pm to the night. At this time, the atmosphere rarely produces inversion temperature, which is very favorable for the application conditions. The best way to avoid drift caused by atmospheric inversion is to control the above-mentioned small droplets. For example, spraying herbicide droplets does not contain small droplets. This phenomenon can also be ignored. 2.4 Adding vegetable oil spray aid when spraying When spraying the herbicide, adding 1% vegetable oil type spray aid can increase the viscosity of the liquid, adjust the uniformity of the droplet size, reduce the small droplets, promote the absorption of the herbicide and conduct in the plant. It can increase the efficacy and reduce the cost, and generally can reduce the dosage by 30% to 50%. Under severe drought conditions, the dosage can be reduced by 20% to 30%, and the efficacy is stable. 2.5 aircraft (1) Flight speed The aircraft operates with high-speed flight and strong airflow to break the sprayed liquid into small droplets. According to the research flight speed reduced from 256 km to 128 km per hour, the average diameter of the droplets increased from 170 microns to 330 microns. The helicopter's general speed is 25% to 30% slower than that of the fixed-wing aircraft, but the airflow can still break the droplets, especially It is when the speed exceeds 88 kilometers per hour. In order to overcome the influence of airflow on the droplets, the direction of the nozzle can be changed. The direction of the nozzle is changed to be backward and inclined parallel to the airflow. According to the research, only the direction of the nozzle is changed from downward to backward, and the droplets with a droplet diameter of less than 100 micrometers are reduced. 75%. Correct adjustment of the nozzle direction can reduce the impact of flight speed on drift hazards. (2) The influence of the wing Fixed-wing aircraft wingtips and helicopter propellers produce tiny whirlwind-like vortices that trap herbicide droplets on the boom, increasing the time it takes for the droplets to float in the air, thereby increasing the probability of drift, fixed-wing aircraft No nozzles can be installed at the wing ends 1 to 1.5 meters. The eddy current of the helicopter causes the drift to be not well controlled. Generally, keeping the aircraft body level or slightly raising the head can reduce the drift hazard. (3) The amount of liquid sprayed In order to prevent drift, the amount of sprayed pre-emergence herbicide sprayed by the aircraft is 30-50 liters/ha, and the amount of herbicide sprayed after spraying is 30-50 liters/ha. Yunwu, Yun 11 aircraft, generally not less than 50 liters per hectare. (4) Flight height, spray width Aircraft spraying herbicides use a lower flying height to reduce drifting phytotoxicity. 3 Common problems and solutions in agricultural aviation operations 3.1 Aircraft organization commander Agricultural commanders such as pest control, topdressing and grass killing are not common among plant protection professionals. Some aviation operations management and command are lack of scientificity, and illegal operations are serious. To strengthen the training of agricultural aviation commanders, in order to become a winner, first become an expert, and the use of aircraft operations must be commanded by personnel who understand plant protection. Participate in the professional training of agricultural aviation operations for the operators, systematically train the agricultural aviation operation commanders, learn the guidelines for agricultural aviation, and the knowledge of plant protection in agricultural aviation, reach the operation division, train the signal crew, and correctly select the medicine and foliar fertilizer . Make reasonable mixes and take appropriate and effective application measures according to the weather to ensure effective application. 3.2 Poor effect after adding spray aid Spraying the spray preparation has a poor effect. There are two reasons for this: one is to choose a cheap synthetic synthetic nonionic surfactant, or a mineral oil, or a liquid fertilizer type spray aid, which will fail when exposed to high temperature and drought; The second is to add a vegetable oil-type spray auxiliaries, the concentration is not enough, the traditional method is calculated according to the working area, the new technology is calculated according to the concentration of the sprayed liquid, and the spray amount must be 1% under high temperature and drought conditions. 3.3 About the amount of liquid spray Under high temperature and drought conditions, the amount of liquid spray should be increased appropriately. From the actual situation, it is recommended to work in high temperature and drought conditions to increase the amount of insecticide and disease prevention spray from 20 liters per hectare to 30 to 40 liters. Considering its solubility of 6%, adding 60 grams per liter, to ensure that 3,000 grams of potassium dihydrogen phosphate is sprayed per hectare, the spray volume is adjusted to more than 50 liters per hectare. 3.4 Training issues before the aircraft operation There is a lack of professional training in agricultural aviation operations for relevant operators before agricultural aviation operations. Agricultural aviation technology is high-tech. From the commanding management personnel to the participating operators before the operation, the training needs to be carefully trained. The training content includes airport preparation, operation planning and zoning, mobilization procedures, signals, ground organization and safety guarantee, and agricultural aviation application. Pharmaceutical technology, agricultural aviation technical quality standards, pest control effects and foliar fertilization effect standards, agricultural aviation flight operations safety management, pesticide safety use common sense. 3.5 Reasonable compounding pesticides Before using pesticides and foliar fertilizers, they should understand their characteristics and miscibility. If there is no data, they can be tested on the spot. 3.6 Pilots should conduct agricultural aviation spray technical coach training General Motors of Beidahuang introduced foreign agricultural aircraft in 1985 and introduced advanced agricultural aviation technology. In 1988, Ma Dequan wrote the "correct adjustment and use of aviation spray machinery", China Agricultural Publishing 1985 "Soybean Chemical Weeding Technology" 》, 1988 “New Plant Protection Practical Technologyâ€, 1987 “China Farming Farmland Weeds and Controlsâ€, 1995 “China Farmland Weed Chemical Controlâ€, 2010 “Green Agriculture Plant Protection Technology †and other published books, special topics Introduce agricultural aviation spraying technology. In 1988, the Academic Journal Publishing House published the book "The Herbicide Spraying Technology" edited by Wang Xianfeng and Xin Mingyuan, detailing the aviation spraying herbicide technology. In 2007, China Agricultural Press published the "Agricultural Aviation Technical Guide" edited by Guo Qingcai. In 2016, Wang Xianfeng's "Safe and Efficient Use of Herbicides" system summarized agricultural aviation technology and promoted it to the whole country. The general aviation company of Beidahuang now has 103 aircrafts. According to the requirements of international agricultural aviation technology, foreign agricultural aviation technical instructors are hired. The pilots have conducted systematic agricultural flight technical training, and the agricultural aviation flight operations are carried out only after passing the examination. At the same time, an informationized command and support system was established. There are nearly 300 agricultural aircrafts in other airlines in China, and pilots have almost no systematic agricultural flight technology training. The amount of liquid sprayed in agricultural aviation operations is generally small, the droplets are small, the operation is not standard, and the drift is serious. Helicopter used in China to spray herbicides has not been carefully tested and demonstrated. The herbicide spraying technology has no rules to follow, and spraying herbicides drifts frequently. 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