INSECTICIDES AND FUNGICIDES. 



Any arsenite of known composition may be applied in quantity to 

 furnish metallic arsenic equal to that in an application of Paris green; 

 whereas any arsenate of known composition may be applied to furnish 

 metallic arsenic equivalent in amount to that used in arsenate of lead. 



For most farm and orchard crops it is unwise to use any arsenical 

 without protecting the plant against foliage damage. The addition of 

 milk of lime affords protection against this arsenical injuiy. Four pounds 

 of high-grade quicklime (95 per cent CaO) are generally sufficient for 50 

 gallons (1 barrel) of spray. The lime should be slaked carefull}^, sieved, 

 diluted to nearly 50 gallons, and the arsenical added slowly with thorougli 

 agitation vmnediatclij before application. 



Arsenical Injury. 



It is evident from what has been stated repeatedlj^ that the carbonic 

 acid and ammonia of tlie atmosphere in conjunction ^vdth dews, fogs or 

 light rains and high temperatures will materially increase the amount of 

 soluble arsenic, ^^^len the arsenic is in solution in the spray liquid, or 

 drops of rain or dew on the foliage, some of it is absorbed bj^ the tissues of 

 the leaf. A very minute amount of absorbed arsenic maj^ have no injurious 

 effect on the cell; but if, on account of a high soluble arsenic content of 

 the spray material, or too long standing of the liquid before drjdng, a 

 sufficient amount has been absorbed, the tissue is killed. Two tj^pes of 

 injury are distinguished (16), — acute poisoning and chronic poisoning. 



In cases of acute poisoning the leaf, or large areas of it, turns black within 

 twenty-four hours after the application; or sometimes, when the insecticide 

 has dried rapidly after application, the blackening may appear after the 

 first period when water has stood on the foliage for some time. In chronic 

 poisoning there are no definite lesions on the leaves, but after two or three 

 weeks they prematurely turn yellow and drop off. Apparently in this 

 type of poisoning not enough arsenic is absorbed to kill the cells outright, 

 but yet enough to interfere with and finally stop the functioning of the 

 cells. 



Certain deductions seem warranted. Conditions favoring a rapid 

 drying of the arsenical and its continuance in a diy state are propitious. 



