INSECTICIDES AND FUNGICIDES. 



Ally arsenite of known composition maj^ 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 injury. Four pounds 

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

 gallons (1 barrel) of spray. The Imie should be slaked carefully, sieved, 

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

 agitation immcdialdn before application. 



Arsenical Injury. 



It is e\'ident from what has been stated repeatedly that the carbonic 

 acid and ammonia of the atmosphere in conjunction with dews, fogs or 

 light rains and high temperatures will materially increase the amount of 

 soluble arsenic. "Wlien the arsenic is in solution in the spray liquid, or 

 drops of rain or dew on the fohage, some of it is absorbed by the tissues of 

 the leaf. A verj'' minute amount of absorbed arsenic may 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 drjang, a 

 sufficient amount has been absorbed, the tissue is killed. Two types 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 

 weelcs 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 ^\•ith 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 dry state are propitious. 



