1921 ENTOMOLOGICAL SOCIETY. 51 



8. When plants are not set out until the flies are known to be present and 

 to be laying eggs, the first application should apparently be made on the third 

 day after the setting out or, in the case of radishes, the third day after the earliest 

 plants have come through the soil. The reason for this is that we must try to de- 

 stroy the eggs and prevent the entrance of the tiny maggots into the root. As eggs 

 sometimes hatch in two days it would be unsafe to postpone treatment later than 

 the third day, unless of course the weather was cool, when an extra day might be 

 allowed. 



9. The best length of time between applications may vary somewhat from 

 year to year because of variations in weather but, judging from our results on 

 radishes this year, a five days interval is better than a week. 



10. The presence of a mixed fertilizer (4-8-4) did not make much difference 

 in results on radishes (It was not tried on cabbage). There was a little higher 

 percentage of infestation on the fertilized part, but not sufficient to justify one in 

 concluding that the fertilizer was the cause. 



11. Much time was devoted to determining how the corrosive sublimate 

 controls the maggot. Strange to say our results this year are almost directly 

 opposite to those in 1919. The difference in results may be partly due to the 

 great difference in the .seasons themselves, and partly to the different methods 

 employed in the two years. In 1919 our results indicated that corrosive sublimate 

 controlled only by repelling the larva?, but this year they indicated that it 

 controlled by killing most of the eggs and also many small larva? and some larger 

 larva? and by repelling larva? from the plants. 



THE CONTROL OF >THE CABBAGE ROOT MAGGOT IN BRITISH 



COLUMBIA. 



R. C. Treherne, Entomologist in Charge for British Columbia, and 

 M. H. Ruhman, Assistant Entomologist. 



During 1919 the experiment conducted for the control of the Cabbage Root 

 Maggot (>Choi-tophila bra^sicae) on both cabbages and cauliflowers proved the 

 superiority of the Mercury Bichloride treatment over other remedial measures, 

 including the tar-paper protector. . The 1920' experiments, therefore, were planned 

 to test the value of Mercury Bichloride on a strictly commercial scale. A field 

 of 25,000 Early Jersey Wakefield cabbages was chosen, and four applications 

 were planned with Mercury Bichloride in solution at the rate of 1 oz. to 10 

 Imperial gallons of water. The first application was to be given three days 

 after transplanting, and this was to be followed by three further applications 

 at ten day intervals. Close watch was kept for the deposition of the first genera- 

 tion eggs and for the first appearance of adults. Transplanting took place in 

 the field on April 25th this year and on the few days following. The materials 

 for application were in readiness for the third-day treatment but, inasmuch as 

 no eggs were yet laid and no flies had been seen, it was decided to withhold 

 any action. The first adults seen in the field were observed on May 5t.:i 

 and the first eggs were laid on May 10th. Hence the first treatment took 

 place on May 11th, or sixteen days after transplanting, or in other words, 

 again, exactly in time for the scheduled second treatment. 



The second treatment should have been made on May 21st, but owing to 

 a recent irrigation which left the soil too wet to walk over, it was delayed 



