Machines for Applying Insecticides

Howard Ingerson, Frank Irons.

Machines for applying insecticides are available in many makes, models, types, and sizes. They offer a wide range of selection for different conditions and uses. They save labor and provide more efficient ways to combat pests.

Power equipment is of six types high-pressure sprayers, low-pressure sprayers, air-type sprayers, mist sprayers, dusters, and fog applicators.

The power source usually has been gasoline engines, either by separate engine or through power take-off from a tractor. The trend during the past few years has been toward air-cooled engines for the engine-powered units because they weigh less and are more compact than the water-cooled types. Water-cooled engines are used particularly for the higher horsepower requirements, however, because suitable air-cooled engines have not been available for the larger machines. The engines in use range from one-horse-power, air-cooled types to the large industrial water-cooled engines of 75 horsepower or more.

Tractors, besides hauling the equipment, furnish power to operate the machine. A standard power take-off attachment extends from the rear of the tractor through a power shaft and is connected with the drive shaft of the sprayer or duster.

The vehicles and mountings for carrying the application equipment are: Trailer type, tractor-mounted, motor-truck-mounted, self - propelled, and wheelbarrow and pushcart types.

Trailer-type and tractor-drawn machines commonly are used in orchards and on row crops, especially when heavy machines are required.

Tractor-mounted dusters and low-gallonage sprayers are widely used for field and row-crop applications. This type of mounting is limited to the weight-carrying capacity of the tractor and tires. Motor trucks are sometimes used for carrying orchard and row-crop equipment and they are regularly employed for carrying mist sprayers for shade-tree spraying. Wheelbarrow- and pushcart-type power sprayers and dusters have come into common use around greenhouses, farm buildings, small truck farms, and estates.

Special self-propelled, high-clearance sprayers and dusters have been developed for treating corn for European corn borer and corn earworm. Some of the machines are adaptations of the detasseling vehicles used in the production of hybrid seed corn and have a clearance of 4 feet to 7 feet.

The high-pressure sprayers, commonly spoken of as hydraulic, are designed for working at pressures of 100 to 600 pounds per square inch and are rated in terms of the number of gallons per minute that the pump discharges at a given pressure. The hydraulic pumps have one to four cylinders and are vertical or horizontal. Some are of open-type design. Others are completely enclosed with oil-bath lubrication comparable to tractor and automotive engine design. The tanks are of wood or steel and usually are from 1 to 20 times the capacity of the pump for example, a pump of 7 gallons per minute capacity might be used with a tank of 150 gallons capacity; a 20-gallon pump is used with a 300- or 400- gallon tank.

Uniform and complete agitation of unstable mixtures is essential for satisfactory results. Most sprayers have a mechanical agitator, a power-driven shaft, which extends through the tank and has several paddles on it.

The pumps and other parts that come in contact with the chemicals must resist their corrosive and abrasive properties. Hence, they usually are made of brass, bronze, rubber, stainless steel, and porcelain.

Large, stationary, and high-pressure spraying systems have been installed in some orchards that are too hilly for portable machines. Pipe lines, underground or elevated, carry the spray under controlled pressure to all parts of the orchard. Outlets are provided at intervals along the pipe system for connecting hand-operated spray guns with long-lead hose.

IMPROVEMENTS are being made all the time in the distributing attachments.

To replace the one or two nozzles on the end of a 10- to 14-foot spray rod, the adjustable spray gun was invented and is in general commercial use. The multi-nozzle spray gun, commonly called a broom or spray head, later came into general use. Now we have attachments to make the spraying of large orchards automatic. They are best suited to sprayers with a pump capacity of at least 20 gallons a minute.

High-pressure sprayers equipped with special booms have been perfected for row crops, including potatoes and tomatoes. The booms are arranged to cover 2 to 30 rows or swaths of 6 to 40 feet. The number of nozzles per row and their arrangement on the boom depend on the crop, plant growth, and coverage needed.

LIVESTOCK SPRAYING requires high pressure to drive the spray material through the hair or wool and to cover the animals evenly and completely. Adjustable-type spray guns are used. Clusters of nozzles that direct the spray from underneath the animals complete the operation.

High-pressure sprayers are used also for spraying shade trees and sanitation spraying to control flies and mosquitoes.

The pumps used in low-pressure spraying are mostly of the gear type. They generally have either bronze or brass parts, resist corrosion, and are suitable for spraying solutions and emulsions. They are not suited for use with suspensions that carry abrasive chemicals. Such sprayers have been introduced into the cotton areas. They are mounted directly on a tractor and operated by power take-off.

AIR SPRAYERS use air as the carrier for the spray chemicals. The air blast replaces the water-carrying power of high-pressure and high-gallonage machines. The fans or blowers in air sprayers are of three types axial, radial, and centrifugal.

The requirements of air spraying are: Proper balance between the volume and velocity of air; nozzles adapted to the particular air velocity and volume; the proper placement of the nozzles in relation to the air stream; and the arrangement of the air-discharge outlet so as to direct the air that carries the spray chemicals so that it will cover the plants.

Air sprayers are rated in terms of air capacity in cubic feet per minute and velocity in miles per hour. They range from 250 cubic feet a minute at 150 miles an hour to 45,000 cubic feet a minute at 100 miles an hour. Some air sprayers are designed for use with dilute spray materials and for applying semi-concentrated and concentrated materials. Other types are designed solely for applying concentrated materials and often are designated as mist sprayers. Mist sprayers are used more and more to control flies and mosquitoes indoors and outdoors and have made sanitation spraying practical and economical. Mist sprayers have been adapted for use on shade trees to save labor and materials.

The air-blast machines blow finely divided spray into the trees, and their air-moving capacity should be sufficient to agitate all the air within the tree and displace much of it.

Ralph V. Newcomb and Arthur D. Borden, working in California, determined the discharge volume of spray in cubic feet per minute needed to spray trees of various sizes when the machine is traveling at various specified rates of speed and is spraying trees on both sides of the line of travel. The volumes are given in the table below.

These investigators tell us that a relatively low air velocity works better than a high velocity and causes less injury to the fruit and foliage. With the rates of travel and the discharge volumes shown in the table, an air velocity of 90 to 110 miles per hour at the nozzles is enough. Nozzles should be used which will break the spray up into droplets 30 to 50 microns in size. Such droplets will produce uniform coating of spray on fruit and foliage with very little runoff.

James Marshall, in British Columbia, and others have developed smaller machines, spraying to one side only, which can be operated partially underneath the overhanging branches of the trees. The discharge volume of these machines needs to be only half that of the two-way machines and are therefore smaller and less expensive. Fruit growers in the Pacific Northwest have had satisfactory results with machines having a somewhat lower discharge volume than indicated in the table.

Many insecticides may be used in the air-blast machines at 2 to 5 times the concentration normally employed with spray guns. Much less water is needed. For example, in mature apple orchards in the Pacific Northwest it is sometimes necessary to use 20 pounds of 50 percent DDT per acre per application to control the codling moth. Applied with spray guns and using the DDT at 1 pound per 100 gallons, 2,000 gallons would be needed. With an air-blast machine, the same acre could be sprayed by applying the 20 pounds of DDT in 500 gallons of water. Some saving of insecticide can even be made with the latter method because when such a machine is properly used much less of the spray drips to the ground than when spray guns are used.