26 CIRCULAR 97 7. U. S. DEPARTMENT OF AGRICULTURE 



from a high-pressure reservoir or by an air compressor. Another 

 model has a separate air cylinder that is charged as needed from an 

 air pump or other source of compressed air. 



With a fine spray nozzle and with the aid of a breeze sufficient to 

 give a swath width of 50 feet, effective coverage can be obtained with 

 5 or 6 quarts of spray per acre, although larger quantities should be 

 used if needed. Since 0.1 pound or even less of DDT per acre is 

 sufficient, the concentration should be' reduced to 1 percent to give 

 this dosage. Under favorable conditions good control over a swath 

 width of several hundred feet has been obtained with a finely atomized 

 oil spray containing 5 percent of DDT at the rate of 1 to 2 quarts per 

 acre. In difficult places several gallons of spray may be required to 

 obtain distribution, but in order to reduce labor and transportation 

 of materials an effort should always be made to apply minimal 

 amounts. 



A 25-percent DDT emulsifiable concentrate (p. 14) developed at 

 Orlando formed stable emulsions with many kinds of water, including 

 sea water. Later, at the request of the Armed Forces, a 25-percent 

 concentrate having a higher flash point was developed to reduce fire 

 hazards in storage or during shipment. 



After dilution, water emulsions are applied in the same manner as 

 oil solutions. A mixture of 1 part of the 25-percent concentrate and 

 4 parts of water gives a 5-percent spray, and 1 part of concentrate 

 with 24 parts of water gives a 1-percent spray. Such emulsions are 

 very effective against mosquito larvae when dispersed throughout the 

 water, but when sprayed as a fine mist, the material has a tendency 

 to remain on or rise to the water surface. For this reason the dosage 

 is usually based on the amount per acre rather than on parts per 

 million. 



Emulsions dispersed in water are somewhat more toxic to culicine 

 larvae than equivalent dosages of DDT in oil on the water surface, 

 but they are also more toxic to fish. Therefore, oil solutions are 

 advocated for use on waters containing fish, particularly for the 

 control of anopheline larvae. However, the amount of DDT in 

 emulsion required to kill mosquito larvae is well below the amount 

 toxic to most fish. If the quantity applied is carefully controlled, it 

 may be used where for logistic reasons an emulsion is particularly 

 desirable. Dusts may also be used. 



Under some conditions large breeding areas, such as extensive 

 roadside borrow pits, can be treated with power sprayers mounted in 

 motor vehicles. Various types of power equipment are used for this 

 purpose, as well as for the control of adult mosquitoes (see pp. 32HL0). 

 The use of airplanes for mosquito control is discussed on pages 42-55. 



A household hand sprayer is convenient for treating small scattered 

 breeding places. An oil squirt gun or even a dropping bottle or eye 

 dropper can be used for the same purpose. A few drops of 5-percent 

 DDT solution with good spreading qualities is sufficient for treating 

 a pool of water 10 feet square. 



Effective treatment is possible with small amounts of spray if the 

 equipment is adjusted to produce a fine mist and if weather conditions 

 are favorable. If adequately distributed, 5 quarts of a 1-percent 

 DDT spray per acre is usually sufficient, but a lower concentration 

 should be used if more spray is needed for coverage. A dosage of 



