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i 44 BULLETIN 1357, U. S. DEPARTMENT OF AGRICULTURE a] 
i > = ef 
; 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 — 
i would necessitate several successive applications. 
f 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 larve and pupex. ‘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 larve, ten pup, 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 larve 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 larve which were removed from egg cages immedi- 
ately after hatching and placed on the treated surfaces died in a 
short time, whereas larve 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 larve are hatching and dropping to the ground, aids in 
the control of an infestation. ; 
1 Since the rose plant can not tolerate heavy applications of wood 
ii ashes, it was found sufficient to use a handful per plant every two 
or three weeks. 
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1 
I PREVENTIVE MEASURES 
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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 
larve and pupe 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 under 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 débris 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 greenhouses, 
~ 
rowers 
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