400 JOURNAL OP ECONOMIC ENTOMOLOGY [Vol. 2 



often used against aphides by allowing the gas to remain in the house 

 over night, during which time it usually leaks out. In each case 

 several tubes, each containing several specimens of all stages of the 

 insect were used. Though one or two moths and occasionally a larva 

 were killed after three hours exposure, many were alive the next 

 morning, the gas having been generated about 6 p. m. The strength 

 was then doubled to one ounce cyanide to 600 cubic feet, then doubled 

 again, and finally doubled again to one ounce to 150 cubic feet with- 

 out killing the majority of the larva or moths in an hour's exposure, 

 but seriously injuring the plants at the latter strength. Mr. H. F. 

 Hall, formerly horticulturist of this station, who has had extensive 

 experience in greenhouse fumigation, tried similar experiments in a 

 small greenhouse in Massachusetts with the same results. All further 

 experiment with fumigation was therefore dropped. 



Arsenate of Lead. Arsenate of lead was then applied to all the 

 plants in the affected houses at the rate of three pounds to the barrel. 

 Many of the worst infested plants were first cut back. This was 

 applied in a novel, but exceedingly effective and practical manner. 

 The tank in which manure water is mixed and the pipes leading from 

 it to all parts of the houses, were flushed out. The arsenate of lead 

 was then mixed up in the tank, hose was attached at each outlet in 

 the houses and when all was ready a score of men commenced spray- 

 ing, and in an hour and one half the three acres of plants had been 

 thoroughly sprayed without the use of a pump. The application was 

 repeated about a week later. Inasmuch as the eggs are laid on the 

 old foliage and the young larvfe feed upon it, there can be no doubt 

 of the efficacy of arsenate of lead, but its effect was obscured in this 

 case by the almost total parasitism of the eggs. Nevertheless, it prob- 

 ably aided greatly in killing off larvjB and those w^hich hatched from 

 the few unparasitized eggs, for on November 17 larvae could still be 

 found in some numbers on individual plants here and there. It is 

 questionable whether spraying with arsenate of lead would be desir- 

 able on roses except in cases of serious infestation, owing to the 

 spotting of the foliage, but this might be avoided by dusting with dry 

 arsenate of lead. Paris green, dry and sprayed, with and without 

 lime, has been tried by growers in the past, but there is always danger 

 from burning the foliage. 



Handpicking. There seems to be no reason w'hy the pest cannot be 

 entirely controlled in rose houses by reasonable diligence in hand- 

 picking. This has been practiced for years in some houses where the 

 insect occurs but has never become numerous enough to cause trouble. 

 From our observations we feel that there can be no doubt that hand- 



