10 



BULLETIN 796, U. S. DEPARTMENT OF AGRICULTURE. 



Table II. — Relative effectiveness of a single fall application of stated doses of 

 p-dichlorohenzene. 1916-1918. 



Observation. 



Application per tree. 



Check un- 



I ounce. 



§ ounce. 



J ounce. 



1 ounce. 



treated. 





10 



4 



6 

 25 

 11 



4.1 



2.5 



70 



88 

 61 

 27 

 90 



9 



3.3 



1 



88 



272 



226 



46 



98 



6 



2.1 



.36 

 95 



298 



256 



42 



85 



6 



2 



.28 

 96 



224 



Number of trees not infested 



22 





202 



Total number of larvae 



1,669 

 44 





Average number of larvse per tree for trees infested . . 



Average number of larvse per tree for total number 



of trees 



8.2 

 7.4 













The time of application varied from the last of August to the last 

 of September, yet in no case was there a very decided departure from 

 the general average of control given in the table. In some cases when 

 application was made about the 25th of August the fumigation was 

 apparently over a little too soon, indicated by a slight infestation of 

 newly hatched larvae. On the other hand, applications made the last 

 of September, while entirely effective, had the disadvantage of in- 

 complete evaporation. The ideal time apparently was in early Sep- 

 tember, approximately the 10th. 



In 1917 about 80 trees were treated at Springfield with a 1-ounce 

 dose each. One plat received one application on July 7; one plat 

 two applications, the first on July 7 and the second on August 24 ; and 

 one plat one application on August 25. The plat receiving one appli- 

 cation July 7 gave a control of 45 per cent when examined on October 

 11. The plat receiving two applications gave a control of 96 per cent, 

 and the plat receiving one application on August 25, 90 per cent. 

 Table III gives the results of this treatment. 



Table III. — Relative effectiveness of one and tico applicatimvs per season of a 

 1-ounce dose of p-dicJiloro'benzene per tree, Springfield, W. Va., 1917. 



Applications. 



Dates of 

 exami- 

 nation. 



Niunber of trees — 



Number of active 

 larvae. 



rercent- 

 ageof 

 control 



Number. 



Date. 



Treated. 



Ex- 

 amined. 



Total. 



Average 

 per tree. 



1 



July 7 

 /..-do... 

 \Aug. 24 



Aug. 25 



Oct. 11 

 }...do... 



Oct. 16 



29 

 38 

 13 



20 

 20 



13 



28 



66 



5 



8 

 169 



3.3 



.25 



.6 

 6 



45 



2 



% 



1 



90 



Check 

















The difference in control between the plat treated twice and that 

 treated once on August 25 is too slight to be of special importance, 

 and certainly not sufficient to warrant the double application in prac- 

 tice. Aside from consideration of economy two applications per 



