CONTROL OP WHITE GRUBS. 



3 



Experiment II. — Use of Carbon Bisulphide in Killing White Grubs. 



How applied 



Center of stool. 



12.5 cc. eacli side of stool 



25. cc. on each .side of stool. 

 In center of stool 



Depth of i When 

 injection i examined 



5 inches. .' 5 days later 



i> inches.. 



Per cent 



of grub.s 



killed 



60 

 65 

 75 

 78 

 76 

 90 

 66 



As a result of these experiments it was seen that car])on bisul- 

 phide was a good killing agent, and that the best results were ob- 

 tained by putting the charge in the center of the stools of cane at 

 a depth of about three inches. It was also noted, however, that se- 

 vere injury resulted to the cane plants from the carbon bisulpliide 

 when amounts greater than 12.5 cc. were used. 



An experiment was then conducted at Guanica Central, under 

 the direct supervision of Mr. C. T. Murphy, to test out the value 

 of carbon bisulphide on a field scale. Some thirty-three odd acres 

 of land planted to sugar cane were used, arranged in five different 

 sections of 3, 3, 4, 6, and 4 plots, respectively. One check plot was 

 left in each section. 



The carbon bi.sulphide was injected by the use of several "Pal 

 Injectpurs" imported from Germany at a cost of .^^31 .57 each. Tliey 

 were so arranged that any amount of liquid desired could be injected 

 at one time. The only drawback in the use of these instruments 

 Avas the action of the carbon bisulphide on the rubber <'onnections 

 and leather washers. These very quickly disintegrated, and the small 

 pieces of rubber and leather clogged up the holes througli which the 

 liquid was forced. Specially devised rubber connections finally over- 

 came this difficulty, however. 



Carbon bisulphide was found to be a most disagreeable and dan- 

 •lerous li(|ui(l to handle, for although no serious accidents happened, 

 numerous burns about the hands and face were experienced by tlie 

 men who applied it. 



Tn all. eight thousand eight hundred pounds of this material 

 were used in the experiment at a cost of six cents a pound. The 

 •;ost of application was $67.05. The cost of material and labor for 

 the application of fifteen grams per stool of cane amounted to $15.53 

 per acre; for the application of thirty grams per stool. $31.0(5 pei- 

 acre. The following tables give the results of the experiment : 



