No. 6. DEPARTMENT OF AGRICULTURfi;. 517 



The chief argument urged against the use of home-made poisons is 

 the trouble and labor of preparing them, the advantage of Paris 

 green being that it i» ready to use just as it comes from the store. 

 But the addition of lime when using the latter alone has come to be 

 generally recommended. This really destroys the ready-to-use argu- 

 ment in favor of Paris green. It is only a step further to prepare the 

 home-made poison. Why not take this step? Thus preparing a 

 mixture of known composition and avoiding all the uncertainties of 

 the commercially prepared article. 



Several commercial substitutes for Paris green have been intro- 

 duced, most of them as arsenoids, or arsenates of different deriva- 

 tives. In general, it may be said of these that they are all open to 

 the same objectionable uncertainties that Paris green is, and Lhey 

 may thus be put in the same catagory. The freshly prepared home- 

 made mixtures are very much better as far as remaining in suspen- 

 sion is concerned; for after the precipitate is dried it cannot be re- 

 duced to a state of division equal to the floccules produced in the 

 liquid. For this reason alone, then, the home-made preparations 

 are preferable. . - - 



A number of preparations have been introduced under different 

 patented trade names. Experience and examination have shown 

 few, if any, of these possessed of exceptional virtues over the 

 '•'straight" goods. As a rule, therefore, it is safest for the fruit- 

 grower to give these special preparations a wide berth, unless their 

 advertised recommendations are supported by the strongest evi- 

 dences of chemical examination, or the strictest practical trial that 

 can possibly be given. 



Bordeaux Mixture. 



This compound, discovered accidentally in France about twenty 

 years ago, has become perhaps the most widely used spray mixture 

 of any kind. It is by far the most effective fungicide known, as many 

 trials in all parts of the world have demonstrated. It consists essen- 

 tially of copper hydroxid precipitated from a solution of copper sul- 

 phate b}^ caustic lime (calcium hydroxid). The copper is the active 

 jirinciple of the fungicide; that is, the effectiveness of the mixture in 

 destroying a fungous disease, or preventing its development, is due 

 wholly to the presence of the copper. Lime has been shown to pos- 

 sess, at best, only very weak fungicidal properties. The lime used 

 in the preparation of Bordeaux mixture may, therefore, be considered 

 as merely an agent to convert the copper sulphate into a less injuri- 

 ous copper compound. In the form of the sulphate, it is perhaps a 

 more effective fungicide, but it is then so injurious to the foliage of 

 growing trees and plants, unless used too dilute to be effective, that 

 its conversion into an insoluble and therefore less injurious form, is 

 necessary. It is for this purpose that the lime milk is used. 



