INSECT ENEMIES OF EASTERN FORESTS 55 
in the older, conventional spray concentrations, 400 to 700 gallons of 
water were used per acre. It has been fully demonstrated that oT 
centrated sprays distributed from aircraft or by mist blowers (fig. 1) 
are usually more effective and far less expensive than the coarsely 
atomized dilute sprays applied from the conventional type of spraying 
machines. Ordinary dusting of insecticides, in some cases, may be 
less troublesome, but is effective e against fewer pests and results in poor 
adherence and wastage of materials. 
A small power sprayer or a mist blower mounted on a wheelbarrow 
or on a garden tractor may be used for treating small groups of trees 
not over 35 feet high. To insure satisfactory coverage of the taller 
trees, small power sprayers should be equipped with an extension spray 
rod to which is attached a disk or vermorel type of nozzle. Power 
sprayers capable of maintaining 300 to 400 pounds’ pressure at the 
nozzle have been used for many years for spraying large shade and 
roadside trees and extensive woodland areas. The W orthley type of 
spray nozzle has been in general use on such sprayers. ‘This method 
of spraying woodlands and shade trees, using large quantities of 
coarsely atomized dilute sprays is at best a slow, “laborious, and expen- 
sive operation. 
Prior to recent improvements in spraying apparatus for use in air- 
craft, and before the development of power mist blowers, the high- 
pressure sprayers mounted on trucks were the most practical and ‘ef- 
fective means of spraying large areas. The development of new in- 
secticides, most of which can be used effectively in concentrated forms 
of solutions, emulsions, and suspensions, and also the improvement 
of distributing apparatus for installation in aircraft, makes it more 
economical to spray large areas from the air. Power mist blowers 
recently developed by the Division of Forest Insect Investigations 
have proved most efficient for spraying large shade and roadside trees, 
forest plantations, and woodland areas that are in small blocks or have 
roads or passable fire lanes at intervals of about 500 feet. 
AERIAL DUSTING AND SPRAYING 
Prior to 1940 airplanes had been used in forest-insect control, mainly 
for dusting insecticides over large maccessible woodlands. Although 
large areas could be covered quickly by this method, it was difficult 
to control the dust cloud. In general, adherence of the dust to the 
foliage was poor. 
During World War II, a number of new insecticides appeared on 
the market, many of which can be used effectively as concentrated 
sprays. Because of these new materials and the recent improvements 
in distributing apparatus for use in airplanes and helicopters, aerial 
application of insecticides is now becoming a general practice for 
Jlarge woodland infestations. Helicopters have the advant age over 
airplanes in that they can land and take off from very small open 
areas. They have greater maneuverability and can be flown more 
slowly and nearer the treetops with safety. However, an airplane 
can carry a much larger pay load than a helicopter, can spray a wider 
swath, and can cover an area much faster. 
To obtain the maximum efficiency in distribution and coverage, the 
application of insecticides from either type of aircraft should be made 
when the wind velocity is not much more than 5 miles per hour, and 
