16 



SCIENTIFIC AGRICULTURE 



Janiiaiv. 1921. 



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as stated before, all the readily available data which 

 can be put in tabular form and which are reasonably 

 comparable. 



The dusts used in all the above experiments have as 

 main eon.stituent.s sulphur and arsenate of lead. But 

 most of the experimental work of the writers has been 

 connected with dusts having copper as the main fun- 

 gicidal basis, and these experiments have not been in- 

 eluded in the above tables. There is considerable 

 reason to suppose, and this will be dealt with in a later 

 article, that the copper arsenic dust as used in Nova 

 Scotia has a considerably higher fungicidal value than 

 90-10 sulphur lead arsenate dust, at least in cool clim- 

 ates. In addition it must be remembered that in prac- 

 tically all the above experiments the dust was used at 

 an unfair disadvantage. That is to say the dust was 

 applied at regular stated intervals in the same manner 

 as the spray, and this is decidedly not the best way to 

 use dust to the best advantage. 



Taking all these facts into consideration and regard- 

 ing the matter purely from the standpoint of relative 

 efficiency in (a) fungus control (b) l)iting insect con- 

 trol, it must be admitted that dusting wins. 



Tlhere still remains the control of the sucking in- 

 sect. On this point there are no experimental data, for 

 it is generally conceded that while sucking insects can 

 be controlled with spray, they have not been satis- 

 factorily controlled with dust. But the problem is not 

 incapable of solution. Professor Whetzel gives many 

 instances of successful control with nicotine saturated 

 dust. In Nova Scotia, Professor Brittain who has 



1.- — Dusted arsenicals and sprayed arsenicals ara 

 both efficient if properlj- applied. 



2. — ^Finely ground sulphur dust has a distinct fun- 

 gicidal value, the percentage of control secured depen- 

 ing upon local and seasonal conditions. 



3. — ^Under certain conditions, dusting may give as 

 good control of apple scab as spraying, but under other 

 conditions and especially against a severe natural out- 

 break, it is somewhat inferior.'" 



Speaking of 1919 he says: "The past season was a 

 very bad one for apple scab, nevertheless, a number of 

 growers are known by the speaker to have obtained 

 most excellent results from the use of 90-10 sulphur 

 lead arsenate dust. We have examined orchards in 

 which it would be hardly possible to better the results 

 obtained by the use of any material. We have seen 

 dusted and sprayed trees side by side in which the 

 former were superior, though both were greatly 

 superior to the untreated trees. On the other hand in 

 our own experiments, though we have obtained satis- 

 factory^ commercial control in some cases, in no case 

 have the results been as good as regards control of 

 apple scab, as have been those secured from either lime- 

 sulphur or Bordeaux in approved strengths. In many 

 cases they have been quite unsatisfactory. 



The writers have had, at least with some dusts, sim- 

 ilar experiences to those of Prof. Brittain, but at the 

 same time have had many experiments where dust was 

 superior to spray. 



From Tables 4 and 5 it will be seen that as far as 

 experimental data goes dusting has proved slightly 

 more efficient than spraying, and these tables include, 



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