74 PROCEEDINGS OF NINETEENTH FRUIT GROWERS' CONVENTION. 



PROCEEDINGS OF THE THIRD DAY. 



Thursday, November 7, 1895. 



The convention met in pursuance to adjournment. Vice-President 

 Weinstock in the chair. 



PARIS GREEN AS AN INSECTICIDE. 



Reasons for Its Occasional Failure. 



Essay by Alexander Craw, Quarantine Officer, State Board of Horticulture. 



The use of Paris green for the destruction of the larvae of the codlin 

 moth, and all masticating insects that prey upon foliage or fruit, is 

 practically beyond the experimental stage. But the occasional failure 

 of it, even in the hands of careful and experienced orchardists, would 

 indicate that there is still need for study and investigation. 



The general supposition reached, in cases where spraying has not been 

 effective, is that the Paris green has been adulterated. This is true in 

 too many instances, but the orchardist or sprayer is sometimes to blame, 

 and I will point out some of their shortcomings. 



To guard against fraud in the purchase of Paris green, it is advisable 

 for orchardists to send to a reliable house, even though small amounts 

 are required; or it could be obtained from the manufacturers in large 

 quantities, through the Fruit Exchanges, for the benefit of orchardists. 

 In this way a guarantee could be secured as to its purity. As a business 

 proposition, the manufacturer will see that it is to his interest to furnish 

 it just as produced by chemical action in the tanks, and not afterwards 

 adulterated with arsenic to bring it up to the necessary percentage and 

 add weight. 



In its pure state it is insoluble in cold water, and when used in the 

 proper proportions for certain plants or trees will not injure the foliage; 

 whereas, if arsenic has been added, it is soluble and burns the leaves. 

 In the manufacture of Paris green the precipitate in the tanks is placed 

 on filters and cleansed by washing away all particles soluble in water. 

 It is then dried and pulverized and is ready for use. The finer it has 

 been ground the more satisfactory it will be as an insecticide, the more 

 readily will it be kept in suspension in water, and be the more thoroughly 

 diffused over the surface of the fruit or leaves in spraying. This fine- 

 ness is a very important point, as it is more readily taken up by the 

 very minute worm as soon as it hatches from the egg. An insect that 

 is nearly microscopic in size will not pick up any gritty substance in 

 preference to the delicate fruit upon which the female moth has by in- 

 stinct placed the egg. Unscrupulous dealers sometimes adulterate Paris 

 green with chrome green, which is nearly the same color, but costs two- 

 thirds less, and is useless as an insecticide. 



