24 LEAD ARSENATE. 



bottom, and tube d about halfway down. Some of the finer particles 

 still remain in suspension in tubes c and d, and the distinguishing line 

 between the water and the main body of the precipitate is indistinct. 

 After fifty minutes tube b is scarcely more than halfway down 

 while the others have practically all settled to the bottom. 



III. ACTION OF LEAD ARSENATE ON FOLIAGE. 

 GENERAL DISCUSSION. 



The fact is well known to entomologists, fruit growers, and others 

 that the foliage of the stone fruits is very susceptible to injury by 

 many substances used as insecticides and fungicides, notably arseni- 

 cals and Bordeaux mixture, when applied as a spray in sufficient 

 strength to destroy insects and fungi. This is particularly true in 

 regard to the peach, which seems to be the most delicate and easily 

 injured of them all. For this reason entomologists have been en- 

 deavoring for many years to find an insecticide that would destroy 

 leaf-eating insects and not injure the most delicate foliage. The list 

 of substances which may be used is somewhat limited, because of the 

 fact that whatever the material may be it must be comparatively 

 cheap and in such a physical condition as to be easily and thoroughly 

 applied. There is no effective insecticide of this class known at the 

 present time which can be used on the peach without more or less 

 risk of injury. As a result of this condition, many peach growers 

 have given up the use of arsenicals, and, in fact, in some sections many 

 orchards have been abandoned entirely. This is a serious problem, 

 and if a successful method can be discovered of combating these de- 

 structive insects without injuring the tree or fruit it will mean millions 

 of dollars to the peach industry. When lead arsenate was first used 

 it was thought that it possessed all of the necessary qualifications and 

 would prove to be the ideal insecticide. It is of inestimable value 

 and is extensively used on apple and other more hardy foliage, and 

 even on the peach it is often used without injury, as shown by many 

 reports on the subject and as personally observed by the authors. 

 Some of the statements in regard to this point which have appeared 

 in several experiment station bulletins and other reports on the sub- 

 ject are quoted as follows: Fernald states that "it [arsenate of lead] 

 can be used in large proportions, if necessary, even up to 25 pounds 

 to 150 gallons of water, without injury to the foliage. " a "It does not 

 injure the foliage of the most delicate plants, even when used in as 

 large a proportion as 25 pounds, or even more, to 150 gallons of 

 water." 5 Marlatt: "It may be used at any strength from 3 to 15 



a Massachusetts Hatch Exper. Sta., 1894, Bui. 24, p. 7. 

 & Agriculture of Massachusetts, 1897, p. 355. 



