50 THE KEGPOKT OF THE No. 36 



FURTHER DATA ON PHORBIA BRASSICAE. 



L. CAESAR, O. A. C, GUELPH. 



1. Numerous tests made not only by the writer and his assistants, but also 

 by Gibson, Brittain, and Treherne, have proven beyond question that corrosive 

 sublimate in solution will control the cabbage maggot both on cabbage and cauli- 

 flower. Many growers, largely due to the influence of Mr. A. H. MacLennan, 

 the vegetable specialist, and his predecessor Mr. S. Johnston, have used this sub- 

 stance on their plots for several years with excellent results : so that it is now 

 long past the experimental stage. 



2. Our own experiments in 1919 and 1920 have shown that this substance 

 will also control the radish maggot. Two applications are all that a grower 

 can afford to give to radishes because they are such a low-priced crop that more 

 than two would make the growing of them unprofitable. To treat radishes suc- 

 cessfully they must be grown, in rows, not broadcast 



3. Our experience Avith creosote clay has not been satisfactory. Some of the 

 compound was made by ourselves, using air-slaked lime instead of clay, and some 

 was obtained from Nova Scotia. On radishes it failed to control the maggot, and 

 on half the cabbages treated onoe it so stunted the plants that we dare not repeat 

 the treatment. The other half showed very little difference from those treated 

 with corrosive sublimate. I have not been able to make sure whether the injured 

 plants were treated with our own or Brittain's mixture. Therefore the substance 

 should be retested. 



4. Judging from results On radishes — all of which were pulled, washed 

 and carefully examined — a strength of 1 to 1,000 (1 oz. to 6 J A imperial gallons) 

 was considerably superior to 1 to 1,600 (1 oz. to 10 gallons) but not much superior 

 to 1 to 1,280 (1 oz. to 8 gallons). As radishes would appear to be well suited 

 for testing the most satisfactory strength of corrosive sublimate to use against 

 Phorbia brassicae, I feel like recommending our own growers tot use 1 to 1,280 



(1 o". to 8 gallons). 



5. Some work was done with cabbage seed beds, this indicated that the cor- 

 rosive sublimate was satisfactory for them also; but further tests are necessary 

 to determine the point definitely under different weather conditions. 



6. Our experiments this year on both cabbage and radishes cause us to 

 think that two well-timed applications at a strength of 1 oz. to 8 gallons of watei 

 are probably all that should be required any year. Often one application would 

 suffice, but variations in weather from year to year are so great that it would 

 not be safe to rely on fewer than two. 



7. The proper time to make the first application to early sown radishes, 

 cabbage and cauliflower requires long and close observation to determine, but its 

 determination is a matter of great importance; for it would often mean the saving 

 of one application. The rule: — to apply the solution first foxtr days after setting 

 out the plants and again twice at intervals of a week — is not a scientific rule and 

 is unsatisfactory. Judging by last year's experience, the first treatment should 

 be just about the time that European plums begin to bloom. Flies began to 

 emerge in our cages last year on May 12th, and were first observed in the field 

 on May 13th. Egg laying in cages began May 17th, and eggs in the field 

 were fairly common by May 22nd. European plums began to bloom in the same 

 district between May 17th and 19th. 



