1909.] PUBLIC DOCUMENT — No. 31. 197 



Ions of water for spraying. Mr. A. II. Kirkland has told me 

 that frequently, for the destruction of gypsy moths, mixtures 

 of 20 to 25 pounds of arsenate of lead to 100 gallons of water 

 are used, and that it is applied either as a si)ray or a stream 

 from the machines, depending largely upon the height of the 

 trees that are being s])rayed. Where the moths arc numerous, 

 and are found upon the foliage of shrubs in wood lands, these 

 as well as the trees are sprayed. The amount of drip from 

 sprayed trees dej^ends very largely upon how the arsenate mix- 

 ture is applied. If applied in the form of a spray, with care, 

 less escapes from the foliage to the ground or grass beneath 

 the sprayed trees than when applied in a stream. During the 

 past summer the writer visited several sections in the gypsy moth 

 district, and observed that the foliage of shrubs under trees 

 that had been sprayed some weeks before still had a sufficient 

 amount of arsenate of lead adhering to be easily seen by the 

 naked eye, and was informed by one engaged in the moth work 

 that it adhered to the foliage so tenaciously that sufficient re- 

 mained after several heavy rains to kill the caterpillars. 



It is at once apparent that the amount of the poison used in 

 spraying that will accumulate upon the grass under sprayed 

 trees will vary very greatly according to the method of applica- 

 tion, the velocity of the wind and other circumstances, and could 

 hardly be expected to be the same in two cases of treatment. 



As stated in Bulletin No. 131 of the Colorado Experiment 

 Station, " Arsenical Poisoning of Fruit Trees," by Dr. Wm. P. 

 Headden, all of the arsenate applied to the foliage must even- 

 tually reach the ground, either by being washed by rains from 

 the leaves or carried with them when they fall from the tree. 

 Three sprayings in a season, using 10 gallons of a mixture of 6 

 pounds of the arsenate to 100 gallons of water for a tree, mean 

 that eventually there will find its way to the soil 1.8 pounds of 

 pasty lead arsenate, equivalent to .9 of a pound of dry arsenate. 



A mixture of 10 pounds of arsenate of lead to 100 gallons of 

 water contains 45.3 grams of the arsenate to the gallon. In the 

 case of cow N"©. 1, 29 grams, administered at the rate of a gram 

 per day, produced violent symptoms of poisoning. With animal 

 Ko. 2, 1G.5 gi'ams, given in daily doses of one-half gram per day, 

 caused violent purging, loss of appetite and paresis. No. 3 took 



