Dusters use air to distribute dry materials. They are used in nearly all fields of insect control as the sole means of treatment or to supplement sprayers.

They are of two general types. Single-outlet dusters are used primarily for dusting in orchards. Multiple-outlet dusters with flexible conductor tubes and spreader nozzles at the ends of the tubes are designed for direct application of dust to field and row crops.

Dusters can be used only when there is little air movement. The dusts adhere less well than liquids. Dusters have the advantages of being lighter in weight and they can carry enough insecticide for long periods of operation. Dusting is popular in places where water supplies are limited.

Fog applicators were developed during the Second World War primarily for spraying enclosed space. Some have been used to control flies and mosquitoes in buildings and outdoor areas. Few are used by farmers; they are generally considered unsatisfactory for providing adequate residual deposits and coverage because they rely on air drift to carry the insecticide.

Sprayers and dusters have to be cleaned and oiled systematically. The corrosive and abrasive properties of spray and dust materials make it essential that tanks and dust hoppers be emptied and cleaned at the end of each day of use. Pumps and all accessories should be washed out to reduce corrosion and nozzle-clogging troubles. Pumps and engines must be drained during freezing weather. Lubrication of all wearing parts according to the manufacturer's instructions will allow the equipment to operate smoothly and increase its useful life. Replacement or repair of wearing parts as needed is good economy.

HOWARD INGERSON joined the Bureau of Entomology and Plant Quarantine upon graduation from Pennsylvania State College. Later he managed commercial orchards in Ohio. Since 1935 he has been agricultural sales manager and research representative of a firm in Lansing, Mich.

FRANK IRONS is an agricultural engineer in the Bureau of Plant Industry, Soils, and Agricultural Engineering. He is leader of a research project that studies machinery used to control pests and plant diseases. He is stationed in Toledo, Ohio.