6 FARMERS’ BULLETIN 595. 
contain 33.15 per cent of arsenic oxid. Experiments have shown 
that the triplumbic form is too slow in its insecticidal action to 
justify its use against tobacco hornworms. The diplumbic form is 
the one that should be used. Jn order to be sure of receiving the 
diplumbic form, demand that the manufacturer and dealer guarantee 
that the arsenate of lead you buy contains at least 30 per cent of arsenic 
oxid (As,0;) in which not more than 1 per cent is free or water-sol- 
uble. This grade was the one used in all the experiments men- 
tioned in this bulletin. It is necessary to have a low percentage of 
free, or water-soluble, arsenic in order to insure against burning the 
tobacco. 
WHEN TO APPLY ARSENATE OF LEAD. 
The first application of arsenate of lead should be made when 
tobacco worms become too numerous to be kept off tobacco by the 
hand-picking that is usually done while hoeing, suckering, or topping 
tobacco. In some years a second and even a third application may 
be necessary. The time for making these applications will be indi- 
cated by the numbers of eggs and young worms appearing on the 
tobacco. For further discussion of this heading see figure 2. 
DOSAGE OF ARSENATE OF LEAD REQUIRED. 
When tobacco is small and has not begun to lap in the row an 
application of 34 pounds of arsenate of lead per acre will be efficient 
if carefully made. Full-grown tobacco should receive not less than 
5 pounds per acre. Of course the weight of the ashes or other carrier 
used is in addition to the weight of the arsenate of lead. In water 
spray use not less than 3 to 4 pounds per 100 gallons of water. 
COST OF ARSENATE OF LEAD. 
The special grade of powdered arsenate of lead recommended for 
use on tobacco will cost about 22 cents per pound at the factory in 
100-pound kegs. The freight will be about 1 cent per pound, mak- 
ing the total cost 23 cents per pound to the grower. Therefore a 34- 
pound dosage will cost about 80 cents, while a 5-pound dosage will 
cost $1.15. In 1913 powdered arsenate of lead retailed at Clarks- 
ville, Tenn., for 25 cents per pound. A 2-pound dosage of Paris 
green costs from 50 to 55 cents, while a dosage of 14 pounds, which is 
the smallest which should be applied, will cost about 31 to 35 cents. 
If the comparative cost of Paris green and arsenate of lead were the 
only question to be considered, it would be useless to recommend 
arsenate of lead. The cost, however, for the careful grower should 
be a matter of strictly secondary consideration. The certainty of 
not burning the tobacco should more than compensate for the extra 
cost of this insecticide. 
