8 BULLETIN 875, U. S. DEPARTMENT OF AGRICULTURE. 
In case of leaf injury the cause of which is doubtful, it is ad- 
visable to pick several affected leaves, pack them in a moist wrapper, 
and send them either to the Delta Laboratory or to the plant 
pathologist of the nearest State experiment station. 
HOW TO APPLY POISON. 
AMOUNT REQUIRED PER ACRE FOR EACH APPLICATION. 
The quantity of calcium arsenate required for each application 
varies somewhat with the machinery utilized and with other condi- 
tions, such as the size of the plants, etc., but generally it has been 
tound that at least 5 pounds per acre are necessary to make a satis- 
factory application. Where the machines are operated by experi- 
enced men, and especially by Government experts who have con- 
ducted this work for a number of years, it has been found that thor- 
cughly satisfactory results can be secured by an average appiication 
of about 4 pounds per acre. But where the work is conducted upon 
« practical farm basis, the dosage used has averaged not less than 5 
pounds per acre. Anyone attempting the operation for the first 
time is more likely to average in the neighborhood of 7 pounds per 
acre for each application. As calcium arsenate at present prices aver- 
ages $0.25 per pound, any reduction in the amount required for each 
application is quite an important item, but to be on the safe side it is 
advised that until farmers are more thoroughly familar with the 
operation the application should be excessive rather than too light. 
Properly conducted, the operation has a very large margin of profit 
and it is poor economy to risk this profit by attempting to save a 
pound or two of poison per acre. 
The greatest factor for further saving in the amount of poison re- 
quired lies in the improvement of dusting machinery. The figures | 
which have been quoted above apply only to the machines which are 
now in use in this work, and it is hoped that by further 1mprove- 
ment of this machinery it will be possible to reduce the amount. In 
fact, considerable progress has been made in this respect. When 
the first experiments were started with power dusting machines it 
was found impossible to control the weevils on an acre of cotton with 
less than from 12 to 15 pounds of poison dust. If the dust could be 
broken up into its finest particles and efficiently distributed, there 
would be enough material in about every 2 pounds of pcison to dust 
an acre satisfactorily, but the present machinery is not equal to the 
task of delivering the dust in this form. This matter is being studied 
very carefully with the hope that further improved machinery can 
be devised. 
