INSECTICIDES AND FUNGICIDES. 25 



The percentage of copper varies in different brands from 1 .5 per cent to 

 as much as 25 per cent, being, of course, higher in the powdered copper 

 fungicides than in those which contain various percentages of water. 



In case an insecticide which contains copper, e.g., Paris green, is included, 

 the guaranty states the amount of copper present as copper of Bordeaux, 

 and in addition may also state the total amount of metallic copper in both 

 the fungicide and the insecticide. In this case the copper of Bordeaux 

 should be used as the basis for calculating the value of the substance as a 

 fungicide. To the purchaser who has been accustomed to thiiilcing in terms 

 of 4-4-50 Bordeaux mixture, this statement of ingredients may mean but 

 little. For this reason, Table II on page 33 is presented, interpreting the 

 guaranties in terms of the standard 4-4-50 Bordeaux. 



Now, while copper is the onlj^ active fungicidal principle in many of 

 these materials, the value of a fungicide does not vary directly as the per- 

 centage of metallic copper. The physical character after it is diluted 

 determines its power to cover and adhere to the foliage of the plant to be 

 protected. A fungicide which is washed from the foliage with the first 

 rain is worthless. It is just as important that the commercial substitute 

 shall on dilution produce a ' voluminous gelatinous precipitate which 

 "stands up" well as it is for the home-made Bordeaux. Commercial 

 fungicides which lack this physical character are deficient in adhesive 

 ciuality, and are therefore inferior to home-made Bordeaux, although 

 they may contain as much copper. 



The final test of the efficiency of a fungicide, however, is its proved ability 

 in the field or experimental plot to check the disease for which it is used. 

 It has been demonstrated in the field that many of these commercial copper 

 preparations have value, but we know of no case in which carefully con- 

 firmed and repeated experiments by unbiased experimenters have shown 

 them to be equal in efficiency to freshly prepared Bordeaux mixture. 

 They are being rapidly improved, however, and we do not despair of seeing 

 on the market within a few years an entirely satisfactory commercial 

 Bordeaux preparation. 



(3) Pickermg Sprays. 

 These fungicides, variously called Woburn Bordeaux, lime-water Bor- 

 deaux, or Pickering sprays, were devised and investigated by Bedford and 

 Pickering (34) of the Woburn Experimental Fruit Farm in England. They 

 are made by mixing clear saturated limewater with dilute solutions of 

 copper sulfate. It is claimed that they are more economical than Bordeaux, 

 in that they contain no excess lime, and the copper is more efficient. They 

 are said to deteriorate less rapidly than Bordeaux and are more easily 

 applied. They have been but Httle investigated or used in America. 

 Cook (35), however, after three years' tests, finds them just as effective 

 as Bordeaux 4-4-50 for control of diseases of potatoes and cranberries in 

 Maine and New Jersey. They did not injure the foliage, possessed good 

 covering and adhesive properties, and apparently possessed the same 

 stimulative properties. These sprays have not been used in Massachusetts. 



