ACTION OF LEAD AESENATE ON FOLIAGE. 43 



foliage in 1907 from the stronger application and very marked injury 

 in 1908 from both strengths. No injurious effect on the fruit could 

 be detected. 



Three applications of lead acetate at the rate of 2.7 ounces to 50 

 gallons of water produced no injurious effect on fruit or foliage in 

 either 1907 or 1908. Three applications of lead acetate at the rate 

 of 5.4 ounces to 50 gallons produced no injurious effect in 1907 and 

 slight injury to foliage in 1908. The use of the latter strength showed 

 a very marked effect on the fruit in reducing the injury caused by 

 insects. This material would probably prove very effective as an 

 insecticide if applied frequently enough or if the applications were 

 followed by a few days of dry weather. 



No injury was caused to the foliage or fruit of the peach in 1907 or 

 1908 by three applications of sodium acetate and acetic acid, acetic 

 acid alone, or sodium nitrate of the strengths in which they would 

 occur in making 1 J pounds of lead arsenate without removing these 

 products and making up to 50 gallons. 



As far as the protection of the fruit from insect injury is concerned, 

 the lead arsenate was a success. 



GENERAL DISCUSSION OF PROBLEMS INVOLVED IN THE INVES- 

 TIGATION. 



Naturally, the first question asked will be, Why did no injury 

 result to the peach in 1907 from the application of lead arsenate, 

 while in 1908, when the applications were made in the same way 

 and of the same strength, serious injury resulted? Though our 

 present knowledge is not sufficient to give a positive answer to this 

 question, some very interesting results bearing on this point have 

 been obtained. 



LEAD NITRATE VS. LEAD ACETATE. 



Contrary to the opinion held by many, lead arsenate made from 

 sodium arsenate and lead nitrate did not cause any more injury than 

 that made from sodium arsenate and lead acetate. Cases reported 

 in which it has been more injurious may have been due to the pres- 

 ence of lead nitrate in considerable excess, for lead nitrate, as these 

 experiments have shown, is considerably more caustic in its effect 

 on foliage than lead acetate. Lead arsenate prepared from lead 

 nitrate possesses several qualities which make it slightly more 

 desirable for spraying purposes than that prepared from lead acetate. 

 These have been pointed out in Part II. It would be more dangerous 

 to use, however, if not properly made that is, if the lead nitrate were 

 present in any considerable excess over that sufficient to combine 

 with all the arsenic. The injury to the foliage caused by lead acetate 

 appeared to be local in character, as it did not cause the leaves to fall 



