46 BULLETIN 1243, U. S. DEPARTMENT OF AGRICULTURE. 



a home-mixed material. Where dusting sulphur is available, it 

 is recommended that the grower obtain the ingredients and mix 

 them himself. 



Used as a spray, calcium arsenate is unsafe without an excess of 

 lime. At the rate of H pounds per acre, with 3 pounds of rock 

 lime freshly slaked, or hydrated lime, it is comparatively safe. In 

 two experiments no plant injury occurred, and excellent control was 

 obtained. In experiment 1(a) (Table 11) 30 per cent of foliage 

 injury occurred, however, and it should not be used when magnesium 

 arsenate is available. In experiment 7 results identical with those 

 following the use of zinc arsenite were obtained. 



The calcium arsenate used in all these experiments was of the very 

 highest grade. The water-soluble arsenic content of this material 

 did not in any case exceed 0.13 per cent, expressed as metallic arsenic. 

 iDferior grades of this compound should be very cautiously applied. 

 The bean plant is more susceptible to arsenical injury than the 

 cotton plant, and grades suitable for cotton dusting may not be 

 suitable for use on beans. 



LEAD ARSENATE. 



For two seasons lead arsenate proved too injurious to bean foliage 

 to warrant its use in the Southeastern States. Under conditions of 

 severe infestation, the protection afforded the foliage is sufficient 

 to make it appear that good results are obtained, but the arsenical 

 injury is serious enough to reduce greatly the normal yield. 



Injury to foliage from lead arsenate used as a dust ranged from 

 60 per cent with the material undiluted to 15 per cent when diluted 

 with 9 parts of hydrated lime. The reduction in yield ranged from 

 59 to 15 per cent below untreated checks which were injured by 

 the bean beetle from 25 to 70 per cent. Slight increases in yield 

 resulted from treatment under conditions of medium and heavy 

 infestation when injury by the bean beetle to untreated checks was 

 35 to 70 per cent. The previous season this material was even more 

 injurious, and experiments were therefore reduced during the second 

 season. 



Injury to foliage from lead arsenate as a spray at 2 pounds per 

 acre ranged from 25 to 40 per cent when rain water was used, and 

 from 15 to 65 per cent when water from a stream was used. A 

 reduction of 3 1 per cent in yield occurred under conditions of medium 

 infestation when the untreated check plat was injured 40 per cent 

 by the bean beetle. It is quite possible that lead arsenate can be 

 used more successfully in the North when the beetle reaches that 

 section, but in the Southeast it is unsafe. Rain water should be 

 used in sections where the water contains soluble salts which de- 

 compose lead arsenate and cause an increase in soluble arsenic. 



Lead arsenate corrected with zinc carbonate, according to sug- 

 gestions from Dr. William Moore, may probably be used success- 

 fully on beans. Additional work on this point is necessary. 



This arsenical is more repellent to the adult bean beetle than 

 magnesium arsenate, zinc arsenite, or calcium arsenate. 



The lead arsenate referred to is a good grade of the commercial 

 lead arsenate, or di-lead arsenate, which is termed ''dilead ortho- 

 arsenate, PbHAsO 4 " by McDonnell and Smith. 10 



m Jour. Amer. Chem. Sob., vol. 38, No. 10, October, 1916, p. 2030. * 



