106 



or curl of leaves at the tip of the plant, since otherwise it will kill the 

 corn. By field experiments made with it in August, 1911, from 60 

 to 86 percent of the bugs were killed with a 4-percent. solution on corn 

 about two feet high. It was applied with a portable "automatic" 

 pump which forced the fluid out by air-pressure in a small solid 

 stream and not in a spray. The emulsion was made by dissolving 

 eight ounces of soap, by boiling, in a gallon of water, adding two gal- 

 lons of kerosene to the hot solution and pumping the mixture back 

 into itself in a forcible stream for several minutes, until it made a 

 uniform, cream-like mixture from which the oil would not separate on 

 standing. This gallon of "stock emulsion" was diluted by adding to 

 it fifteen and a half gallons of water to make a mixture containing 

 4 percent of kerosene. 



Easier methods of preparing the kerosene-soap emulsion and sim- 

 pler methods of applying it to the corn were found unsatisfactory, 

 sometimes because comparatively few of the bugs were killed, some- 

 times because the corn was injured, and sometimes for both of these 

 reasons together. 



Tobacco Preparations. — In 1910, experiments made in southern 

 Illinois by Mr. L. M. Smith, in charge of our chinch-bug work in that 

 part of the state that year, showed that a spray of tobacco extract 

 known as "Black Leaf 40" was much more easily prepared than the 

 kerosene emulsion, was more deadly to the chinch-bugs, and was not at 

 all injurious to the plants to which it was applied. Precise tests of 

 this insecticide were made by Mr. Flint at Plainview in August, 1911. 

 In the first of these a half ounce of the tobacco extract was diluted 

 with a gallon of water in which half an ounce of soap had been dis- 

 solved, and the solution was applied in a small straight stream, by 

 means of a portable automatic pump, to infested corn from twenty 

 to forty inches high. Twenty-four hours later twenty hills of this 

 corn taken at random were carefully examined, with the result that 

 on three of the hills 75 percent of the bugs were dead, and on seven- 

 teen hills 90 percent, making an average of 88.5 percent for the whole, 

 while the corn was not injured in the least. In four similar experi- 

 ments the Black Leaf 40 was reduced to a fourth of an ounce to 

 the gallon of water, and the soap was increased to one and a half 

 ounces. In these the percentages of bugs killed ranged from 74 to 

 85.5 and in still another experiment, with half an ounce of Black 

 Leaf 40 and half an ounce of soap, the number of chinch-bugs killed 

 on the different hills was estimated at 75 to 90 percent. 



The cost of the materials necessary for a thoro treatment of in- 

 fested corn varies of course with the size of the plants. In corn six 

 feet high it averaged $5 per acre ; in that six to fourteen inches high 

 it averaged $1.30 per acre. With the small portable spraying appara- 

 tus used in these experiments it would have taken one man eighteen 



