﻿44 BULLETIN 1351, U. S. BEPABTMENT OF AGRICXJLTUEE 



The foregoing figures were based on only one treatment, whereas 

 the maximum insecticidal effect could be obtained only by continu- 

 ous leaching of these materials over an extended period, which 

 would necessitate several successive applications. 



In an establishment containing 40,000 rose plants two carloads of 

 each of these materials were used during the spring of 1922, The 

 mixture was applied on the soil several times at intervals of about 

 two weeks. Occasional soil examinations during the season dis- 

 closed very few larvae and pupse. The balls of soil around the roots 

 of 293 plants were examined and the larval and pupal stages infest- 

 ing 19 of them were counted. Nine larvae, ten pupae, and one newly 

 emerged adult were found, and all were alive. Several other con- 

 trol measures were also being practiced, however, and it is therefore 

 a matter of conjecture whether the lightness of this infestation can 

 be credited entirely to the use of the wood ashes and tobacco dust 

 treatment. 



Other experiments were performed to determine the effect on 

 newly hatched larvae of tobacco dust containing not less than one- 

 half of 1 per cent of nicotine. A layer of this dust one-fourth inch 

 deep was spread over the entire surface of the soil in flowerpots 

 every two weeks. In some cases this treatment was followed by 

 watering. All larvae which were removed from egg cages immedi- 

 ately after hatching and placed on the treated surfaces died in a 

 short time, whereas larvae placed in a vial on untreated soil imme- 

 diately showed greater activity by boring down below the surface 

 in a lively manner. 



These experiments indicate that a layer of tobacco dust on the soil 

 from March to September, and the subsequent leaching of this mate- 

 rial when larvae are hatching and dropping to the ground, aids in 

 the control, of an infestation. 



Since the rose plant can not tolerate heavy applications of wood 

 ashes, it was found sufficient to use a handful per plant every two 

 or three weeks. 



PREVENTIVE MEASURES 



Several preventive measures may be practiced to keep rose houses 

 free from infestation with the strawberry rootworm. The fact has 

 been established that some houses have become infested with the 

 larvae and pupae of this insect by filling the beds with soil in which, 

 strawberry plants have been growing. In order to destroy these 

 stages the soil should either be composted for several months or be 

 sterilized before it is used. It is desirable to avoid using soil in 

 which strawberry plants have recently been grown. Propagate 

 young plants in separate houses free from the insects, and tinder no 

 conditions expose them to contamination by proximity to infested 

 beds or houses. In purchasing plants be certain that they are free 

 from all stages of this pest, and that all precautions have been taken 

 by the propagator to protect them. Keep the greenhouse free from 

 rubbish and burn all dead leaves and debris removed from the beds. 

 as well as the tops of the bushes which are removed when cut back. 

 The importance of such precautionary measures is too frequently 

 underestimated, and due consideration must be accorded them for 

 preventing insects from gaining a foothold in greenhotises. 



