■!! 



pure powder would indicate that it is not the amount of powder that 

 proves fatal but that it is the fact of a few grains of powder coining in 

 contact with the body of the worm. All of my dilutions above 5 times 

 the weight of powder show that its efficiency is thus very much im- 

 paired, and I am satisfied that while almost infinitesimal doses are suf- 

 ficient to produce death when powder is pure, they will not suffice in 

 the presence of adulterations. lam quite convinced that 5 dilutions 

 is the limit of safe adulteration, and think that I should hesitate to 

 recommend over 3. The age of the worm when treated is of consider- 

 able importance in this connection, as young worms are destroyed with 

 much greater certainty than older ones. Pure powder exposed on the 

 leaves of cabbage plants for periods of thirty minutes, fifteen hours, 

 and twent3' hoars, killed with as much certainty as fresh powder. Old 

 powder, which had stood one year in a candy jar without cover, killed as 

 well as fresh powder. This last was used, diluted 3 times, in field work 

 and did good execution. 



One pound of powder diluted with 3 pounds of flour and carefully 

 used in a TVoodason double-cone bellows was sufficient to dust one 

 acre thoroughly. Four was the only adulteration used. 



EXTRACTS OF PYRETHRUM. 



Water extract — 1 ounce pyrethrum ; 1 pint water. 



AJcholic extract — 1 ounce pyrethrum ; 1 pint alcohol. 



These were thoroughly tested and the tests repeated several times, 

 with very unsatisfactory results. 



The water extract was made by stirring together the ingredients. 

 Only the liquor was used which was kept in a tightly closed jar. 



This extract destroyed rapae at an average rate of 50 per cent, up to 

 4 dilutions, and at 5 dilutions failed entirely. In full strength it was 

 uot nearly so efficacious as dry powder, even on ra/pce, and it did not 

 affect brassicce at all. 



The alcoholic extract was made by repercolation with about 80 per 

 cent, alcohol. This I anticipated w r ould bear a large number of dilu- 

 tions, and it was used in an extensive series of tests in the cages and 

 jars. Up to 5 dilutions it killed fairly well and a few were destroyed 

 above this, but not enough worth mentioning, only a small or weak 

 worm dying. This test was repeated several times and a new extract 

 w r as made, but with little better results. The new extract killed about 

 50 per cent, very slowly at 10 dilutions. Both extracts spoken of 

 above were applied as spray, except that in jars a feather was used and 

 the worms thoroughly wetted. 



On Aphis brassicce. 



Pyrethrum in several forms was used on this insect with unsatisfac- 

 tory results, the action being, when applied pure or in strong mixtures? 



