JOURNAL 



OF 



ECONOMIC ENTOMOLOGY 



OFFICIAL ORGAN AMERICAN ASSOCIATION OF ECONOMIC ENTOMOLOGISTS 



Vol. 10 AUGUST, 1917 No. 4 



LEAD ARSENATES, STONE FRUITS, AND THE WEATHERi 



By Geo. P. Gray 



The appearance of an unusual number of canker worms in the prune 

 and apricot orchards of the Santa Clara Valley (Cal.) in the spring of 

 1915 caused a great many of the orchardists of that section to make 

 one or two sprayings of lead arsenate in order to prevent defoliation 

 of the trees. The worms were well controlled within a short time, 

 but some two or three weeks after the application of the poison, it was 

 noticed that the trees began shedding their foliage. The injured 

 leaves were specked with brown spots, each speck being dead leaf 

 tissue. (See pi. 16.) Some of the fruit was also injured in the 

 same way. The defoliation in some of the orchards amounted to 

 perhaps 50 per cent, while in others the injury was not as serious. 

 Defoliation and fruit dropping was quite general, however, wherever 

 lead arsenate had been applied for the canker worms. 



It so happened that practically all of the lead arsenate used on 

 prunes and apricots in the vicinity was purchased from a single firm. 

 Some of the orchardists had never before been obliged to use an 

 arsenical and so the use of arsenicals in general was condemned. 

 Others thought that they had been supplied with a poor grade of 

 arsenical, and threatened law-suits. The office of the County Horti- 

 cultural Commissioner was besieged with inquiries as to the cause of 

 the trouble. The situation was so unusual that the Commissioner 

 (Mr. E. L. Morris) called upon the Insecticide and Fungicide Labora- 

 tory of the Agricultural Experiment Station for assistance in the 



1 Presented before the State Fruit Growers' Convention, Stanford Universitj^, 

 July 26-31, 1915. 



