8 BULLETIN 875, U. S. DEPARTMENT OE 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 

 found 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- 

 oughly satisfactory results can be secured by an average application 

 of about 4 pounds per acre. But where the work is conducted upon 

 a 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 familiar 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 improve- 

 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 poison 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. 



