August, '17] GRAY: ARSENATES AND STONE FRUITS 389 



fact, this has been done in the Santa Clara Valley for a number of 

 years with only occasional bad effects. This year, however (1915), 

 has shown that this procedure is not a safe one and some other way 

 must be chosen if the growers do not wish to take the consequences of 

 defoliation and fruit drop due to the effect of unfavorable weather 

 conditions upon acid lead arsenate. 



The weather conditions that are believed to favor the decomposition 

 of acid lead arsenate are a succession of light rains extending over a 

 period of several days, continual foggy or damp "muggy" weather, and 

 more or less warmth. A heavy rain is not as serious as a mist, for 

 if there is a decomposition of the arsenate, a rain sufficient to drip 

 from the leaves may wash off the soluble arsenic before its absorption. 



Weather Record for the Period of Spray Injury 



The following weather record covering the period of spray injury 

 has been kindly furnished by Mr, W. H. Ward of Morgan Hill, Cal., 

 who was one of the orchardists to suffer quite seriously from spray 

 injury. 



The rain records are taken in the morning about 7 a. m. and are as 

 follows : 



April 20 66 inch 



April 26 27 inch 



April 27 14 inch 



April 28 11 inch 



April 29 11 inch 



May 1 11 inch 



May 3 38 inch 



May 4 97 inch 



May 9 20 inch 



May 10 22 inch 



May 11 16 inch 



May 13 18 inch 



May 16 31 inch 



May 23 07 inch 



The spraying was done on the Ward ranch on April 19 and on the 

 afternoon of April 20. The weather was damp when the spraying was 

 done the first day and it rained the night following. The spraying was 

 finished the next afternoon. 



The amount of acid lead arsenate used was from 4 to 4| lbs. to 100 

 gallons of water. This was about the amount used by the other 

 growers. The injury was noticed about two weeks after the applica- 

 tion of the spray. 



Theories Confirmed by the Investigation 



As previously noted, five samples of lead arsenate paste were col- 

 lected during the progress of the investigation. These samples were 



