123 



attenuation of the oil, namely, in giving the mixture a consistency which 

 extends its actions, and in addition, witii the soa[) emulsion, the insecti- 

 cide value of the soap. A further objection to the water and oil mixture 

 is that wherever the spray collects in drops, as it inevitably will, free 

 oil will separate in sufficient amount to injure foliage. An application 

 also which depends for its success on the perfect workingof a complicated 

 apparatus, liable at any moment to get out of order, is hardly a safe one 

 to put into the hands of an indifferent laborer. 



Ar seriate of lead, — This arsenate, which originated with Mr. F. 0. 

 Moulton, of the Gypsy Moth Commission, and is reported to have such 

 excellent insecticide qualities, both by the commission and by Mr. 

 Fernald, who has experimented with it, is the most promising of the 

 new mixtures which have come out during the past year. Our experi- 

 ments at Washington show that this mixture has good grounds for the 

 claims made for it. Its advantages over the other arsenicals, it will be 

 remembered, are its qualities of adhering to the foliage and seeming to 

 lack entirely any caustic properties. We have used it on the tender 

 foliage of the peach and Osage orange at a strength of 1 i)ound to 2 

 gallons of water, with glucose enough added to almost make a syrup, 

 without the slightest inj ury to the plants treated. The mixture adhered 

 to the foliage through several heavy rains, and gives evidence of lasting 

 through the summer. Its insecticide value was tested in experiments 

 with the elm leaf-beetle, which, the j)resent season, appeared in great 

 numbers in the large elm grove on the Department grounds. The 

 experiments were unsatisfactory in one respect, on account of the fre- 

 quent occurrence during the spraying season of rains, which interfered 

 with the results and rendered a number of repetitions of mixtures 

 necessary. 



On May 21 the elm trees were sprayed with the following strengths: 

 1 pound of arsenate of lead and 2 quarts of glucose to 120 gallons of 

 water, to 75 gallons, and to 50 gallons, applying it in each case to eight 

 or ten trees. The check exj)eriment consisted in the application of 

 Paris green, 1 pound to 150 gallons water, to neighboring trees. These 

 applications all seemed satisfactory, with the exception of the weakest 

 mixture of arsenate of lead, which seemed to have had very little effect 

 on the larvjie. The two stronger applications of the arsenate of lead 

 and the Paris green killed at least 95 per cent of the larvne by the 26th 

 of May. The rain seeming to have interfered with the action of the 

 poison, and it being very desirable to exterminate the larvte, a second 

 application was made between the 20th and 29th of May. Arsenate of 

 lead mixed as above and diluted at the rate of 1 pound of poison to (50 

 gallons of water was used, one tree being treated with Paris green at 

 the strength employed in the first instance. Light rains immediately 

 followed the application, and on the 31st of May the larva? were 

 dying, but not rapidly, the Paris green being more prompt in its action. 

 The trees were therefore sprayed again on the 4th of June with a 



