1020 EXTOMOLOGICAL .SOCIETY. vl 



FUETHEB DATA ON THE CONTROL OF THE CABBAGE ROOT 

 MAGGOT IN THE OTTAWA DISTRICT. 



AirniUR Gibson, Chief, Division of Field Crop and Garden Insects; 

 Entomolooical Branch, Department of Agriculture, Ottawa. 



Siueo the ])ublifati()ii, in 1912, of our Bulletin on the cabbage root maggot* 

 we have conducted a number of further experiments on the control of this insect, 

 jiarticularly with corrosive sublimate and tobacco dust and lime. The former has 

 leeeiwd ^^pecial study during the past four years, and we consider its value to be 

 undoubted and that it has now passed the experimental stage having been used 

 with remarkable success under field conditions. Early references in the literature 

 point to the fact that corrosive sublimate has been known as a remedy for the 

 cabbag(> root maggot for over 50 years, and it is remarkable that its value has only 

 been appreciated during comparatively recent years. In the years 1916 and 1917 

 we conducted experiments with corrosive sublimate on a small scale. In 1918, 

 we used in one experiment SOO early cabbage plants. These plants were treated 

 Avith corrc^ive sublimate in the strength of one ounce to four gallons of water 

 on four occasions, namely, on ]May 27th, June 6th, 14th and 23rd. The results 

 from this ex}>erLment were very striking, 96 per cent, of the plants treated with 

 the corrosive sublimate being saved. In the same field in which the experiment 

 was conducted the main cabbage plantatioii was destroyed by the root maggot to 

 the extent of fully 60 per cent. In 1919, over 8,000 cabbage plants were placed 

 at our disposal by ^\r. J. I. Farquharson, who resides on the Aylmer Road, near 

 Ottawa. Of this number 2,731 plants of the varieties Jersey Wakefield and 

 Copenhagen Market were used in one experiment. This block of 2.731 cabbage 

 plants was divided into 38 smaller blocks, of which blocks 1 to 18 inclusive, except- 

 ing blocks 2, 5, 8, 11, 14, and 17, which were left as checks, were treated with 

 commercial corrosive sublimate mixture in the strengths of 1 oz. in 4 gallons of 

 water, 1 oz. to 6 gallons of water, 1 oz. to 8 gallons of water, and 1 oz. to 10 gallons 

 of water, some blocks having four treatments others only three. The plants were 

 put out in the field on ^li\y 12th. The first application was made on the fourth 

 day after planting, the second apjilication six days later and one or two further 

 applications ten days apart, about half a cupful of the mixture being poured 

 around the base of the stem of each plant on each occasion. Each block consisted 

 of 100 plant* excepting the checks which varied from 20 to 36 plants each. Blocks 

 19 to 24 inclusive (100 plants each) excepting checks 20 "and 22 (30 plants each) 

 were used for felt-tarred-})aper discs of various shapes. Blocks 25 to 23 inclusive 

 (100 plants each) excepting blocks 26, 29, 32. 35, and 38 (20 plants each) were 

 treated with tobacco dust and lime in the pro})ortion of 1 part tobacco dust to 

 2 parts of lime, 1 part of tobacco dust to 3 parts of lime, and 1 part of tobacco 

 dust to 4 parts of lime, two, three and four applications being made. 



The results of this ex])eriment arc very striking. Briefly, they are as follows: 



Corrosive Subli:\iatf:. There Avas })ractical]y no difference in the plots 

 tr(^ated with the various strengths of corrosive sublimate. The weakest solution, 

 namely, one ounc^ in ten gallons of water, gave as good results as did the strongest 

 mixture of one ounce to four gallons of water. Three applications, too. are appar- 

 ently equal to four applications. The percentage of plants destroyed by the maggot 



*Biill, 12, Bnt. Br., Dept. Agr.. 1916. 



