December, '10] woodworth: codling moth 471 



done only when their methods become the regular practice of the 

 growers. 



The difficulties met with in the Pajaro Valley in spraying for 

 codling moth have never been discussed except locally, and may be 

 of interest to Eastern entomologists. 



Before the investigation was taken up at Watsonville many com- 

 plaints came to the Department of the burning produced by Paris 

 green and gave occasion for the study of the greens on the market 

 in the state, reported in Bulletin 126, in which it was shown that much 

 of that material contained water soluble arsenic. The outcome of 

 this study was a law defining^ the amount of free arsenic permissible 

 in Paris green which was also adopted in other states and which has 

 resulted in improving the foliage safety of Paris green all over the 

 United States. 



It was soon found that the climate about Watsonville and not the 

 free arsenic in Paris green was the determining factor in the problem 

 in that region. 



The Pajaro Valley opens out on Monterey Bay and lies opposite 

 the Pecheco Pass. The cold winds from the ocean blow across this 

 valley to replace the heated air of the great San Joaquin Valley, just 

 as the winds sweep through the Golden Gate at San Francisco towards 

 the Sacramento Valley. In consequence there are almost daily fogs 

 from the ocean every evening during all the summer. The continual 

 drenching of the trees by these fogs hydrolizes almost all arsenicals, 

 setting free the acid, and after two years of experiment involving 

 losses of thousands of d(>llars in some orchards on account of arsenic 

 injurj^ to foliage, Paris green had to be discarded entirely.' 



During the third year of the investigation it was also clearly seen 

 that none of the commercial brands of arsenate of lead could be safely 

 used in the Valley and that and the following years hundreds of arseni- 

 cals were made up and tested and the solution of the problem finally 

 came from the discovery that certain samples of lead arsenate, both 

 as obtained on the market and made up in the laboratory did 

 not injure foliage, and that these samples were distinguishable 

 bj' the fact that they contained no arsenic acid soluble in ammonia, 

 that is, they consisted of a saturated lead salt. Nearly always by 

 the ordinary methods of manufacture an arsenate of lead consists 

 of an acid salt or a mixture of an acid and a basic arsenate of lead. 



Two of my assistants undertook to work out, as a private venture, 

 a method of manufacture by which a uniform product of this charac- 

 ter could be obtained. They were entirely successful and organized 

 the Cahforhia Spray Chemical Company, largely financed b}- local 

 orchardists, the product of which has contributed in no small 

 degree to the final success of the effort to control this insect. 



