August, '17] GRAY: ARSENATES AND STONE FRUITS 391 



in every case where stone fruits had been sprayed, with acid lead 

 arsenate, more or less injury was apparent. 



Summary 



According to the observations made of stone fruits to which acid 

 lead arsenate had been applied during the month of April, 1915, they 

 showed injury to a greater or less extent. Pome fruits which were 

 sprayed under the same conditions causing the injury as above noted 

 show^ed no injury. Examination of five samples of lead arsenate 

 collected during the investigation represented three different brands. 

 In no case did the analysis reveal the presence of unusual quantities of 

 water-soluble arsenic. The samples were all good grades of acid lead 

 arsenate. According to weather records and to the testimonies of 

 the growers, a period of damp, misty weather prevailed during and 

 after the application of the lead arsenate causing the spray injury. 

 It seems reasonable to conclude : 



1. The acid type of lead arsenate, often labeled " standard," is unsafe 

 to use on the foliage of stone fruits except under favorable weather 

 conditions. 



2. According to weather reports, it appears that during the spring 

 of this year (1915) (particularly during the month of April) unusually 

 unfavorable weather conditions prevailed in the Santa Clara Valley, 

 Cal. 



3. The foliage injury in the orchards of the Santa Clara Valley 

 this spring was due to the decomposition of acid lead arsenate by the 

 weather. 



4. According to previous experience and in accordance with previ- 

 ous recommendations of the University, the basic type of lead arsenate 

 (usually labeled " tri-plumbic " or ''neutral") is a safer arsenical to 

 use on stone fruits and is not decomposed by unfavorable weather con- 

 ditions. This is a slower acting poison, however, than the acid type 

 and would not be as effective unless applied when the canker worms 

 are very young. 



Recommendations 



In looking up the recommendations of entomologists and taking into 

 consideration the experiences previously noted, it appears that there 

 is a choice of three procedures for the control of canker worms : 



1. Banding of trees has been found to give satisfactory results. 

 Essigi may be cited as authority for recommending "tree tanglefoot" 

 for the control of both spring and fall canker worms. 



2. The acid type of lead arsenate may be successfully used on stone 



^Essig, E. O., Injurious and Beneficial Insects of California, pp. 417 and 415. 



