t)8 THE KEPOET OF THE Ho. 36 



It is obvious that sumo of the treatments are entirely inadequate to eontrcil 

 llu' maggot. A few show a decided advantage over the check plots, but not 

 sufficient to make them worthy ol further trial, in view of the very much better 

 results obtained by other materials. In this class may be mentioned nicotine 

 sulphate and clay, nicotine and sulphur, para-diihhiroben/.ene alone, and salt 

 solution in the strength tested. Others actually ai)]ieav to have weakened the plants 

 to such an extent that a greater number succumljeil to the attacks of the maggot 

 Than on the check rows. These include dry lime sul])hur, white arsenic, arsenate 

 of soda and combinations of these compounds. jS'o further discussion is necessary 

 regarding these two classes, all the required facts being found in the table. 



A consideration of the other treatments shows that Plot VI T, (the tobacco 

 dust, corrosive sublimate and clay mixture) gave the smallest number of plants 

 actually destroyed, but Plot I (creosote) is a close second with only one more 

 casualty and with the largest tonnage per acre of any plot, lov\a'r cost of treatment 

 and greater profit per acre. Plot lY (anthracene oil) is only slightly behind the 

 foregoing in number of marketable heads produced, but it also falls below Plot 

 XIII (para-dichlorobenzene and soot) in tonnage per acre. This is probably due 

 to another reason than maggot control as will be seen later. The treatment given 

 to No. V (tobacco dust, white arsenic and clay) is apparently next in efficiency, 

 but this plot also falls below Xo. XIII in tonnage per acre, and even No. XII 

 (para-dichlorobenzene and clay) which lost three times as many plants, has pro- 

 duced a greater weight of head. No. XIII actually comes second in tonnage per 

 acre produced, though l)e]iiii(l the plots previously mentioned in the number 

 of plants free from injury. The plants in this plot were noticeably benefited by 

 the treatment, having a deoj^er green colour of leaf and a healthier general appear- 

 ance than the other plots. The results from the foregoing treatments are con- 

 sidered promising and will be tested further in the " Continuation Plots" of 1920. 

 Tested out on earliest planted cabbage, the relative merits of these materials as 

 compared with the test in the "Continuation Plots*" of 1919, should be clearly 

 indicated. 



THE CONTPOL OF THE CABBAGE ROOT MAO (JOT IN BRITISH 



COLUMBIA. 



M. C. Teehernp:, Entomologist in Charge for British Columbia, and 

 M. H. Ruhmann, Assistant Provincial Entomologist. 



At the request of Mr. Arthur Gibson, Chief, Division of Field Crop and 

 Garden Insects of the Dominion Entomological Branch, the virtue of the corrosive 

 sid)limate treatment for the control of the Cabbage Root Maggot, Phorhia 

 hrasdcw, was tested in- British Columbia during 1919, in comparison with the 

 Tar-paper-disc method of coiitrol. At Mr. Gibson's further request the following 

 report is siibmitted on the record of the experiments performed. 



The Plan of Experiment. 



The work was conducted altogether in the large commercial vegetable-growingJ 

 district of Armstrong, B.C.. where the Cabbage Root Maggot has for several! 

 years exacted a heavy toll. The " block " system of experimentation was adoptedl 

 in preference to the '* row " system. Twelve l>locks were employed, with from! 



