64 THE IJEPOirr OF THE No. 36 



The foregoing treatments are so greatly superior to any of the others that the 

 latter may be disposed of in a few words. The tobacco dust, soap powder and 

 soot mixture is worthy of note as coming next in efficiency to the foregoing and 

 giving a heavy average weight of head. The tar paper discs from which the soil 

 was not removed, Avere markedly inferior to those where this was done. The 

 screens, while giving perfect control, are too costly and their application too 

 laborious ever to come into general use, and in addition, they seem to have a bad 

 effect upon the plants. The tobacco dust and lime, while inferior to the foregoing 

 in maggot control gave, nevertheless, greatly superior results to those of last 

 season. This is doubtless due to the fact that the material was put on fresh when 

 the flies first appeared and then renewed ten days later. The previous season 

 the material was applied several days before the appearance of the flies, a heavy 

 rain intervening between that time and their appearance. The tobacco dust is 

 apparently only effective when fresh and its usefulness is destroyed by a heavy 

 rain. In conjunction with sulphur, washing soda or soap powder, is apparently 

 more effective than with lime. 



It is interesting to note that practically all the substances used in our con- 

 tinuation plots were mentioned by Slingerland in his bulletin on this insect 

 (Bui. 78, Cornell Univ. Agr. Expt. Sta., 1894), though he did not consider them 

 in all the combinations used by us. Among the effective methods he lists screens 

 and tar paper discs; among the ineffective, soot, sulphur and tobacco dust. The 

 two former he did not test himself, but he did some experiments with the latter, 

 which did not turn out entirely satisfactorv'. The material was applied twice, 

 the first time immediately after planting, the second ten days later. He does not 

 state whether the flies were out at the time of the first application, but says 

 that they were abundant at the time of the second. As a resiilt of the experiments 

 nearly one-half of the treated plants were salable, while only 90 marketable heads 

 were secured out of 600 of the untreated plants. 



Particularly interesting is his mention of corrosive sublimate in view of tiie 

 success that has lately attended the use of this chemical. On this account we 

 reproduce his remarks in full: 



"An editorial in 1864 {Country Gentleman-, p. 65) states that a contemporary 

 recommends 1 oz. of the substance dissolved in 4 gals, of water. A correspondent 

 of a Canadian Journal {American Cultivator for April 30, 1881) says all of the 

 London market gardeners secretly use a solution of ^ oz. of this substance in 

 4 gals, of water for these maggots. He has used the solution quite extensively, 

 using enough to saturate the ground. But it is not clear from the account whether 

 it is applied as a preventive or whether it kills the maggots. We have little faith 

 in its effectiveness but it should be further tested." 



The foregoing shows that this material was in use many years ago and it seems 

 strange that it never seems to have made headway until recently. The reason for 

 this may have been that the average person takes no notice of the infestation 

 until the plants begin to wilt, when the maggots are well grown and it is too late 

 fo apply control measures. All our experiments indicate that to control the maggot 

 a material must be either a repellent, in which case it should be applied at planting 

 or before the flies appear or, it should be one that will destroy the eggs of very 

 young larvae, a fact that has often been lost sight of in studies of this pest. If the 

 cabbage can be protected for even two weeks after setting out, our experiments 

 indicate that it stands a very good chance of surviving the attacks of the maggot. 



