Spraying

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spraying,

horticultural practice of applying fungicides, insecticides, and herbicides, usually in solution, to plants. It may be accomplished by various means, e.g., the watering can, sprinkler attachment, spray gun, aerosol bomb, power spraying machine, or airplane. The spraying of powdered chemicals is called dusting. Spraying and dusting are chiefly preventive measures, but may also be used to check the spread of a pest among already infected plants. It is usually necessary for the spray to reach all exposed parts of the plant. The type of spray used and the timing of its application depend on the specific plant and its pest. Copper or sulfur compounds are common ingredients for a fungicidefungicide
, any substance used to destroy fungi. Some fungi are extremely damaging to crops (see diseases of plants), and others cause diseases in humans and other animals (see fungal infection).
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; nicotine, arsenic, or DDT for an insecticideinsecticides,
chemical, biological, or other agents used to destroy insect pests; the term commonly refers to chemical agents only. Chemical Insecticides

The modern history of chemical insecticides in the United States dates from 1867, when Paris green proved
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. A criterion for any spray is that it does not injure the plant itself and that it is as specific as possible for the pest involved, i.e., that it inflict minimal damage to beneficial insects and to wildlife. The danger inherent in the use of poisonous sprays such as DDT cannot be overestimated, particularly in the case of those that are not eliminated or otherwise rendered ineffective (as by antitoxins) by the animals—including man—that feed on sprayed plants and insects, but accumulate in the tissues until a lethal concentration kills the animal or renders it unable to reproduce its kind. Spraying of selective herbicides is used in weedweed,
common term for any wild plant, particularly an undesired plant, growing in cultivated ground, where it competes with crop plants for soil nutrients and water. In their natural habitat, wildflowers and herbs not only provide beauty but function in many useful ways, e.g.
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 control.

Bibliography

See bulletins of the U.S. Dept. of Agriculture.

Spraying

 

the application of material in a dispersed state to the surface of finished and semifinished products in order to impart special physicochemical, mechanical, or decorative properties to them or for the purpose of restoring a defective surface. The coating applied by spraying is held on the surface mainly by forces of adhesion.

A distinction is made among flame, electric arc, powder, liquid, vapor, plasma, laser, and autothermionic emission methods of spraying, depending on the initial state of the materials applied and on the design of the spraying device. The abovementioned methods are used for coating with metals (nickel, zinc, aluminum, silver, chromium, copper, gold, and platinum), alloys (steel, bronze, and so on), chemical compounds (silicides, bo-rides, carbides, and oxides), and nonmetallic materials (plastics). The thickness of the sprayed-on film depends on the method and conditions of spraying, as well as on the properties required. Spraying is also used in the production of thin epitaxial films (for example, films of semiconductors).


Spraying

 

the use of sprayers to apply pesticides in droplet form on trees and agricultural plants to control insect pests, diseases, and weeds. Spraying may also be used for defoliation and desiccation and to protect livestock against warble flies. It is often used for purposes of disinfection and insect control in livestock quarters, grain storage facilities, and greenhouses.

Chemical solutions in water and other solvents, as well as emulsions and suspensions, are sprayed. The effectiveness of spraying depends on the toxicity of the pesticides and the duration of their action, the degree of atomization (large-drop spraying releases drops with diameters of 200–500 microns [μ,] and greater; small-drop spraying involves drops measuring 80–200 μ), evenness of distribution of the pesticide, and conditions of application (air temperature, wind strength, and the presence or absence of dew). Spraying times depend on meteorological conditions and on the biological characteristics of the pests and disease agents.

In conventional, or large-drop, spraying the expenditure of fluid is 400–500 l per hectare (ha) for field crops, 400–800 l/ha for industrial crops, and 800–1,500 l/ha for vineyards and orchards. Small-drop spraying, with a fluid expenditure of 25–100 l/ha, increases the effectiveness of chemical treatment and the productivity of sprayers, facilitates organization of the work in arid regions, and makes it possible to spray fields in strong winds and at the most desirable times. The use of ultrasmall-drop spraying (Russian abbreviation, UMO), which uses 0.5–10 l/ha of fluid with drop dimensions of 25–125 μ, looks promising. Chemicals for UMO that do not need to be diluted are now being produced.

When spraying, it is essential to observe safety measures to prevent possible human poisoning. The application of pesticides is halted three to four weeks before harvesting.