STRAWBERRY ROOTWORM ON GREENHOUSE ROSES 35 
| neath the plants. Because of the fact that the adults showed a 
| marked tendency to feign death, 317 were collected and held in 
_ cages several days for further observations. Less than 3 per cent 
| of these revived, and a total mortality of 97 per cent was therefore 
_ obtained from this fumigation. It 1s advisable to emphasize the 
fact that although fumigation at this strength and duration is con- 
_ trary to the general recommendations for fumigating greenhouses, 
it is an effective though very drastic means of checking the ravages 
_ of the beetles in severe infestations. Moreover, by destroying the 
_ females at this time further egg laying is precluded and subsequent 
_ infestation thereby reduced. 
__ As had been anticipated, some of the young and tender growth 
_ was burned, thus depriving the few remaining adults of their favorite 
feeding places. This injury, however, was only temporary, for three 
weeks later the plants had produced an abundance of newly forced 
_ growth, attributed to the stimulating effect which usually follows 
_ fumigation with hydrocyanic-acid gas, and were in excellent condi- 
tion. During the subsequent months these plants produced a bounti- 
ful crop of cut flowers in comparison with the very inferior produc- 
tion prior to the fumigation. | 
In one establishment during the summer of 1921 approximately 
32,000 plants, including 1,000 newly set young plants in the resting 
or drying-off period, were fumigated at a dosage of 2 ounces of 
sodium cyanide per 1,000 cubic feet of space, with an exposure last- 
ing one and one-half to two hours, at temperatures ranging from 66 
to 88° F., and not one plant was lost or even retarded in general 
growth (31, p. 230). The anticipated burning on the tender growth 
proved to be a negligible factor, since it was removed by the severe 
pruning when the plants were cut back. The results of the experi- 
ments, together with similar ones carried on at Alexandria, Va., and 
_ Baltimore, Md., are given in detail in Table 14. As will be observed, 
several houses received three or four successive fumigations. More- 
over, these tests demonstrated on a practical scale that muslin cur- 
tains (fig. 16) could be used successfully to confine the gas in any 
section of an open-range house. | 
‘During the last three seasons 21 commercial houses, involving 
many thousands of plants, have been fumigated with consistent re- | 
sults, demonstrating the successful use of this gas on a practical and 
commercial scale for controlling the adult beetles. | 
Since a series of three or more successive fumigations with hydro- 
eyanic-acid gas at night, at the rate of 114 or 2 ounces of sodium 
cyanide per 1,000 cubic feet of sp&ce, with an exposure lasting two 
hours, at intervals of three or four days during the drying-off period, 
and with the final fumigation the night before the plants are cut 
back, kills all adults above the ground without permanent injury to 
the plants, fits in with the cultural practice in the summer when the 
beetles are most numerous, and may be applied in individual sec- 
tions of open-range houses by separating them with muslin curtains, 
canvas, or oiled paper to confine the gas, it is without doubt one of 
the most effective and satisfactory means of destroying the beetles. 
