MEXICAN BEAN BEETLE IN THE SOUTHEAST. 45 



ZINC ARSENITE. 



The two commercial grades of zinc arsenite experimented with 

 the past two seasons are unsafe for use on bean foliage. Zinc arsenite 

 does not appear to be as injurious to bean foliage as lead arsenate. 

 The injury to the bean plant is different from that caused by other 

 arsenicals, as burning of the foliage does not always result, but the 

 plant is visibly stunted, the color of the foliage turns darker green, 

 and the leaves show a tendency to curl. 



Used as a spray at 1 1 pounds to the acre, reductions in yield below 

 those of check plats were obtained. Under conditions of severe 

 infestation, excellent insect control is apparently obtained, but 

 treated fields do not yield well. On account of the particular type 

 of injury to the crop from use of this arsenical, the injury is likely 

 to be overlooked and the arsenical rated too high unless accurate 

 records of yields are obtained. 



Only one experiment was performed with this material as a dust 

 during 1922. Diluted with hydrated lime, plant injury can be 

 reduced, but this material is inferior to calcium arsenate and magne- 

 sium arsenate on account of toxicity to foliage. It is also physically 

 inferior to calcium arsenate for dusting. 



CALCIUM ARSENATE. 



Calcium arsenate or arsenate of lime is extremely toxic to bean 

 foliage. Injury to foliage when used as a dust ranged from 60 per 

 cent to no injury, depending to a great extent on the degree of 

 dilution with hydrated lime. Reductions in yield occurred in much 

 the same order. It is certain that calcium arsenate can not be used 

 as a dust stronger than 1 to 5 parts of hydrated lime, and that 

 appreciable injury may result in some cases with this dilution. 



This insecticide is the most desirable for dusting, from the stand- 

 point of physical properties. 



Sulphur as a diluent appears to have a slight beneficial effect in 

 reducing plant injury, but not enough to make calcium arsenate 

 safe at stronger than the 1-1-4 dilution shown in the next paragraph, 

 and foliage injury occurred in two experiments to the extent of 10 

 and 20 per cent, respectively. The beneficial action of sulphur is 

 even less noticeable when calcium arsenate is used in greater propor- 

 tions. 



Excellent results have been obtained with a mixture devised by 

 Dr. F. L. Thomas, of the Alabama Agricultural Experiment Station, 

 comprising 1 part of calcium arsenate, 1 part of superfine dusting 

 sulphur, and 4 parts of hydrated lime. Slight injury, however, has 

 occurred under certain conditions with this mixture. Where this 

 occurs, it is suggested that the hydrated lime content be increased. 



Diluted with 9 parts of hydrated lime, the high-grade calcium 

 arsenate used has for two seasons been found safe on bean foliage. 

 Only one instance of injury to foliage occurred, and that only 10 

 per cent. Further comparisons between this cheap mixture of 

 materials, available to most growers, and the more expensive sulphur 

 mixture are necessary. The slight advantage of this mixture over a 

 1 to 9 hydrated lime mixture does not warrant the extra expense, 

 where growers have to purchase this mixture already prepared, 

 since the price is from 2 to 4 times as high per unit of arsenical as 



