56 



PAPEES OX INSECTS AFFECTING VEGETABLES. 



On June 3 the count was again taken, and the row treated with Xo. 

 I had 15 infested plants, a decreased infestation of 32 plants, or 68 + 

 per cent. The row treated with Xo. II had 23 infested plants, a 

 decreased infestation of 63 plants, or 73.2 per cent, while the row 

 treated with Xo. Ill had 13 infested plants, a decreased infestation of 

 75 plants, or 85.2 per cent. 



The following table shows the number of infested plants in the 

 plats before and after spraying: 



Table V. — Results of applications of arsenite of zinc at different strengths against the 



Colorado potato beetle. 



Date. 



Solu- 

 tion 

 Xo. 



Number of 

 infested 

 plants. 



Decrease in 



number of 



infested 



plants. 



Decrease of 

 infesta- 

 tion. 



1911. 

 Mar 31 



I 



II 

 III 



A 



III 

 I 



II 

 III 



47 

 86 

 88 

 33 

 57 

 38 

 15 

 23 

 13 





Per cent. 



Do 







Do 







June 2 



Do 



Do 



June 3 



Do 



Do 



14 

 29 

 50 

 32 

 63 

 75 



29.8 

 33.7 

 56.8 

 68+ 

 73.2 

 K ; 







On June 3 the number of larva? on the plants which were still 

 infested was much smaller than the number present when the spray 

 was first applied. The extent of infestation of some plants amounted 

 to but one or two larvae; these plants, however, were counted in as 

 infested. 



Results. — From the preceding table it will be seen that far better 

 results were obtained where 2 pounds of arsenite of zinc to 50 gallons 

 of water were used. 



The results were obtained more quickly, and a larger percentage of 

 larva? was killed. At this strength arsenite of zinc did not burn or 

 injure the foliage in any way. and without doubt an even greater 

 amount of the arsenical might be used without injury to the plants 

 and with corresponding!}- greater efficiency in killing the beetles. 



ADDITIONAL COPIES of this publication 

 -£i- may be procured from the Superintend- 

 ent of" Documents, Government Printing 

 Office, Washington, D. C , at 5 cents per copy 



