60 



The tollowino- papers were then prosented: 



HYDROCYANIC-ACID GAS AS AN INSECTICIDE ON LOW-GROWING 



PLANTS. 



By E. DwiGHT Sanderson and L\ L. Penny, Newark, Del. 



The desirabilit}' of using a gas as an insecticide upon low-growing 

 plants, more especially for plant lice, Ijut also for some leaf folders 

 and other insects which can not be reached by means of a spray, has 

 long been apparent to entomologists. 



So far as known the only work previously done upon this problem 

 is that of Prof. H. Garman, Avho seems to have been the first to sug- 

 gest such use of a gas. with carbon bisulphide upon the melon louse, 

 mentioned at the meeting of this society in 1893, and his subsequent 

 experiments with hydrocyanic-acid gas in 1894 (Bui. 53, Ky. Agr. 

 Exp. Sta.), and the further experiments of Dr. J. B. Smith with car- 

 bon bisulphide upon the same insect in 1895 (Bui. 109. N. J. Agr. 

 Exp. Sta.). It is believed that neither of these gentlemen, however, 

 have perfected practical apparatus, nor outlined a method for its 

 extensive use in the field. 



Two years ago, under the direction of Prof. W. G, Johnson, we did 

 considerable work with hydrocyanic-acid gas in tents and box frames 

 over trees, and in boxes for nursery stock, in combating the San Jose 

 scale. In one instance several hundred young trees were fumigated 

 with flour barrels. Young apple trees were also fumigated for plant 

 lice with marked success. Having read the experiments by Professors 

 Garman and Smith, this experience with the gas led me to attempt the 

 problem of applying it to use upon low-growing plants during the 

 past spring. 



Carbon bisulphide has not been tried, as the trials already made, 

 including also some recently recorded by Professor Webster, showed 

 that it was very much slower in its action, a serious obstacle to its 

 extensive use. This point might indeed be overcome b}^ using a larger 

 number of coverings, but a large investment in apparatus would pre- 

 clude its use in many instances. Where carbon bisulphide requires an 

 hour to kill plant lice, hydrocyanic-acid gas takes but ten minutes. 

 Thvis in use upon melons, with a cover for each plant, with 100 covers 

 hardly more than 1,000 plants could be fumigated in a day with caribou 

 bisulphide, while five or six times as many could be treated with hydro- 

 cyanic-acid gas. As regards cost of chemicals there is not much differ- 

 ence, though, if anything, carbon bisulphide is slightly more expensive. 

 Both gases are dangerous poisons, but, all things considered, I believe 

 that hydrocyanic-acid gas is possibly preferable to carbon bisulphide 

 in this respect. There is but little danger with h3^drocyanic-acid gas in 

 such small quantities in the open air. the greatest danger being in 



