INSECT ENEMIES OF WESTERN FORESTS 223 



sions for spraying; (3) emulsifiable concentrates, which are mixed 

 with water to form emulsions for spraying; and (4) oil solutions, 

 which are applied directly as sprays. 



For use on ornamental shrubs and trees in parks, and in other 

 situations where applications can be made from the ground, 

 with hand or power sprayers, dusts containing 3 to 5 percent of 

 DDT and sprays prepared from 50-percent wettable powders at 

 the rate of 2 pounds and 25-percent wettable powders at 4 pounds 

 per 100 gallons of water, and emulsions at 0.8 to 8 pounds of DDT 

 per 100 gallons are suitable. 



For airplane spraying a 12-percent DDT oil solution is most 

 frequently used. This is made by dissolving 1 pound of technical 

 DDT in 1 gallon of a mixture of 15 parts (by volume) of benzene, 

 xylene, or methylated naphthalene and 85 parts of Diesel oil or 

 No. 2 fuel oil. This solution is applied at the rate of y 2 to 1 gallon, 

 or y 2 to 1 pound of DDT, per acre. When applied from the ground 

 by power sprayer, the solvents injure foliage, but in the mist 

 developed by airplane or helicopter sprayers the oil evaporates 

 rapidly and very little foliage burning results from the low 

 dosages applied. 



So many new insecticides and combinations of ingredients are 

 now used for specific purposes that, if special problems arise 

 requiring the use of insecticides, it is best to consult an 

 entomologist. 



POWER SPRAYING 



Power sprayers mounted on motor trucks may be used in the 

 control of park- and shade-tree defoliators, but in forests their 

 use is limited to areas along roads or to camp sites and resorts 

 where it is possible to transport this heavy equipment. Because 

 of the height of forest trees, high-power spraying pumps are a 

 necessity; but even with the largest equipment so far developed 

 it is not possible to reach a height of much over 90 feet, nor is 

 it feasible to reach out with spray hose more than 5,000 feet from 

 roadways (fig. 103). Mist blowers and fog machines have been 

 developed for applying light deposits of DDT and other contact 

 sprays to orchard and shade trees, but thus far their use in 

 forest-tree spraying has been limited. 



AIRPLANE SPRAYING 



Since 1926 (52) the airplane (fig. 104) has come into use for 

 spraying forest areas, and the helicopter is now being developed 

 for special work of this type. 



In the early work of treating forest areas from the air, dry 

 dusts, principally calcium arsenate, were used. Airplanes were 

 equipped with hoppers carrying 1,000 pounds of dust which was 

 applied in 150-foot swaths at the rate of 20 pounds per acre by 

 an airplane flying about 40 feet above the tree tops. Costs ranged 

 from $3 to $6 per acre. It was extremely difficult to get a uniform 

 coverage with dry dust, because it drifted badly and did not 

 adhere well to foliage. Although several large forest areas were 

 treated in this manner, the results were only moderately success- 

 ful (152). 



