68 The Spraying of Plants. 



Entomology, in which London purple was used in comparison 

 with several other substances. 1 In this test Paris green proved 

 the most satisfactory, then arsenious oxide, while London pur- 

 ple stood third on the list. The principal objection to the last 

 two materials was that they scorched the foliage of the cotton 

 plants to which they were applied. The conclusion was also 

 reached that it is more economical to apply the powders when 

 mixed with water than in the powder form, only about one-half 

 as much poison being required by the former method. 



The value of London purple as an insecticide was recognized 

 with surprising rapidity. The experiments of Comstock and of 

 Riley were widely copied, and although there were some seri- 

 ous objections to the use of this arseuite, its cheapness and the 

 ease with which it could be applied were greatly in its favor. 

 Cook used it successfully in 1879 against the codlin-moth, and 

 with such recommendations it soon won public favor. The 

 principal objection to its use was the danger of scorching the 

 foliage of the plants, and this probably is the main reason why 

 it did not entirely supersede Paris green. It is also less uni- 

 form in its composition, which renders it of uncertain value. 

 Yet it was only about three years after its introduction that 

 the value of London purple was generally considered to be 

 nearly equal to that of Paris green, and it is so considered 

 to-day. 



Spraying for the Curculio. 



No subject connected with the spraying of plants, with per- 

 haps the exception of the best methods of making the kerosene 

 emulsion, has been the subject of such heated controversy as 

 the spraying of stone fruits with arsenites to protect theni 

 from the curculio. The value of the operation seems to have 

 been first noted by G. M. Smith, of Berlin, Wis. In 1870 

 Riley wrote an article on this practice in which he held it 

 up to ridicule, 8 and the subject was again mentioned by the 

 same writer in an article which states that Smith recommended 

 it "to the Saint Joseph (Michigan) Horticultural Society, and 

 from that time on [the poison] has been occasionally suggested 



Ann. Rtpt. T. & Com. tfAffHc. 1879, 809. 



* Third Kept. State Entomoioffist of Jfi**wrt, 18. 



