﻿STEAWBERBY EOOTWOEM ON GREENHOUSE ROSES 



33 



The powdered sugar was added in the hope that it might prove 

 attractive as a bait, and the arsenical content was increased on the 

 theory that it would be more effective than the 10 per cent mixture. 

 The dust was applied in accordance with the florists' program, i. e., 

 after each syringing, or about two or three times weekly, so that from 

 midsummer until November about 1,500 pounds of this material were 

 used in keeping the foliage covered. During 1922 the insects failed 

 to appear in appreciable numbers, and this infestation was found to 

 be so very materially diminished that it became practically negligible. 

 As a precautionary meas- 

 ure, however, a dust coat- 

 ing was maintained on the 

 foliage from February 15 

 until the plants were cut 

 back or torn out in the 

 summer. As was the case 

 in the first two establish- 

 ments, other control meas- 

 ures were employed also, 

 and reliance was not placed 

 on dusting alone in com- 

 bating the beetles. 



It was unfortunate that 

 the effectiveness of dusts 

 alone, uncomplicated by 

 other simultaneous meth- 

 ods of control, could not 

 have been tested in a com- 

 mercial range ; but the fact 

 that dusting with arsen- 

 icals was the principal con- 

 trol measure common to 

 all three establishments, 

 with the possible exception 

 of a limited amount of 

 hand picking, indicated 

 that this treatment was an 

 important factor in reduc- 

 ing these infestations. The 

 florists who used this dust 

 felt well satisfied with the 

 results obtained from an 

 insecticidal view-point, and because of the fungicidal value of the 

 sulphur in the mixture. 



FUMIGATION 



The use of one of the standard fumigants, such as hydrocyanic- 

 acid gas and volatile nicotine, which are frequently employed in 

 greenhouse fumigation (fig. 15), was given consideration early in 

 this investigation. According to several florists the use of volatile 

 nicotine painted on pipes was entirely ineffective against the beetles 

 {25y p. 70). and subsequent experiments verified this conclusion. In 

 the case of hydrocyanic-acid gas it was necessary to determine the 



Fig. 14. 



Growth made by plant four weeks after 

 being cut back. (See fig. 11) 



