INSECTICIDES AND REPELLENTS 



49 



M 



Figure 21. — Helicopter with thermal smoke generator in operation. 



Spray Materials 



Solutions. — A 5-percent solution of DDT in fuel or diesel oil has been 

 employed most commonly in aerial spraying with small planes. The 

 output of the equipment is adjusted to give a dosage of 2 quarts 

 (approximately 0.2 pound of DDT) per acre, and either the quantity 

 or concentration can be varied to give different dosages. Droplet 

 size and evaporation of solvent can be reduced by the addition of 10 

 to 20 percent of motor oil. The addition of 1 percent of a spreading 

 agent, such as Triton B-1956 (phthalic glycerol alkyd resin), is said 

 to be of some advantage in larvicidal work. The 5-percent solution 

 may be prepared by dissolving technical DDT in the oil or by diluting 

 the 20-percent airplane spray with fuel oil. In larger and faster planes 

 the 20-percent spray is used full strength, and the delivery rate and 

 swath width are adjusted to give 1 pint per acre for the standard 

 dosage. The 20-percent solution is sometimes used to advantage in 

 small planes. 



Emulsions. —Emulsions are employed for control of both larvae and 

 adults, preferably in the smaller planes and under conditions that 

 permit low-altitude flying in order to reduce evaporation before the 

 material reaches the ground. A concentrate containing an aromatic 

 hydrocarbon as the solvent and having a minimum flash point of 

 140° F. (see No. 8) is recommended, since the explosion hazard is 

 slight and this type of solvent prevents complete evaporation while 

 drifting in the air. This concentrate may be used full strength or 

 with only slight dilution with oil when the regular 20-percent airplane 

 spray is not available. 



