56 
PAPERS ON INSECTS AFFECTING VEGETABLES. 
On June 3 the count was again taken, and the row treated with No. 
I had 15 infested plants, a decreased infestation of 32 plants, or 68 + 
per cent. The row treated with No. II had 23 infested plants, a 
decreased infestation of 63 plants, or 73.2 per cent, while the row 
treated with No. 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 
No. 
Number of 
infested 
plants. 
Decrease in 
number of 
infested 
plants. 
Decrease of 
infesta- 
tion. 
1911. 
May 31 
II 
III 
47 
86 
88 
33 
57 
38 
15 
23 
13 
Per cent. 
Do 
Do 
June 2 
14 
29 
50 
32 
63 
75 
29.8 
Do 
II 
33.7 
Do 
III 
II 
III 
56.8 
June 3 
68+ 
Do 
73.2 
Do 
85.2 
On June 3 the number of larvae 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 
larvae 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 correspondingly greater efficiency in killing the beetles. 
ADDITIONAL COPIES of this publication 
*l\. may be procured from the Superintend- 
ent of Documents, Government Printing 
Office, Washington, D. C , at 5 cents per copy 
