MAINE .APPLE DISEASES. 389 



All other things being equal, an article testing rather high and 

 relatively free from sediment would be the more economical to 

 buy. Hydrometers do not detect soluble impurities added to 

 lime-sulphur concentrates for the purpose of increasing their 

 densities. The national law against the adulteration of fungi- 

 cides and insecticides will doubtless prevent this difficulty, but 

 if there is any reason to suspect the character of any brand of 

 goods a sample should be submitted to a chemical examination. 



Before buying any of these concentrated sprays the purchaser 

 should make sure that it is a lime-sulphur compound. At least 

 one other concentrated substitute for bordeaux the name of 

 which indicates that it is some sort of a soluble sulphur prepa- 

 ration has been known to produce disastrous results when ap- 

 plied to apple trees with arsenate of lead in even greater dilu- 

 tions than recommended by the manufacturers. 



Dust sprays. In hilly, rocky orchards where heavy spraying 

 machinery can be hauled with difficulty, and in localities where 

 a plentiful, near-by supply of water is not available, spraying 

 with liquid sprays is attended with considerable difficulty. To 

 meet this difficulty various dry sprays, said to contain approxi- 

 mately the same active constituents as liquid bordeaux mixture, 

 have been advocated from time to time. These are in the form 

 of a very fine powder to be blown forcibly on to and within 

 the foliage by means of specially designed machines, the essen- 

 tial parts of which consist of a rapidly rotating fan, a hopper 

 to hold the powder, and a line or lines of hose to conduct the 

 air blast carrying the powder up among the tree tops. 



In some instances favorable results have been reported for 

 the dust sprays, but in the opinion of the writers their use is 

 not advisable. In 1907 one of us (M.) demonstrated the 

 marked inferiority of the dust sprays as compared with standard 

 5-5-50 liquid bordeaux for the control of the late blight of the 

 potato.* At the same time the late Prof. W. M. Munson of 

 this Station was conducting experiments with dust sprays on 

 apple trees for scab. While these results were never published 

 they were in general similar to those secured on potatoes. 

 Crandall has, however, made and published the results of a very 

 thorough study of the relative merits of liquid bordeaux and 



Morse, W. J. Me. Agr. Exp. Sta. Bui. 149, p. 289, 1907. 



