30 CIRCULAR 639, U. S. DEPARTMENT OF AGRICULTURE 
33). The dust cloud in this case will not rise sufficiently to cause 
discomfort to the operator. When the plants are larger it is impos- 
sible to cover all the foliage by a direct application. Under these con- 
ditions the dust-gun nozzle is held in the center of the space between 
the tobacco rows and the dust allowed to drift onto the leaves. In 
high tobacco the operator should avoid the dust as much as possible 
by directing the nozzle to the rear. When large acreages are being 
treated in this manner the operators of several dusters may walk 
abreast to avoid the dust cloud (fig. 34). 
The frequency and the number of applications necessary to pro- 
tect a tobacco crop will depend mainly on the abundance of beetles 
present during the growing season. Flea beetle infestations vary 
greatly from year to year and from one field to another. From the 
FIGURE 33.—Applying ater to shade-grown tobacco that is less than knee high, the 
nozzle of the dust gun being directed toward the foliage and in front of the 
operator, 
information available at the present time it appears that under the 
usual conditions about one application a week will give sufficient 
protection to a crop. Rotenone-bearing dusts are not effective in 
the shade-tobacco area for a very long period. Under the most 
favorable conditions it appears that the “effectiveness of an applica- 
tion will be limited to about 3 days. Observations indicate, in 
general, that frequent, light applications made throughout the grow- 
ing season exert much more satisfactory control than a small number 
of “relatively heavy applications. 
Applications of barium fluosilicate may be made to control flea 
beetles on newly set tobacco. This poison is effective against both 
flea beetles and grasshoppers, and may be used to control joimt out- 
breaks of these two species on young shade-grown tobacco. To 
obtain an even distribution of the poison it must be mixed with a 
