DISEASES OF CULTIVATED PLANTS 657 



ator should know what disease or diseases he is expecting to prevent 

 by the application of the spray, and should thoroughly post himself 

 beforehand as to the correct times and intervals for spraying for that 

 particular disease. The spray must be applied ahead of the infection 

 periods of the fungi. (2) The spraying should be thoroughly done. 

 In dormant spraying a coarser spray can be used than in summer 

 spraying, because the object is merely to form a complete coating of 

 me spray over the wood. In summer spraying, however, an exceed- 

 ingly fine, mist-like spray reaching every portion of the plant and 

 covering with minute dots, preferably no larger than a flyspeck, 

 every square inch of the fruit and foliage is necessary. It is not nec- 

 essary that the minute specks of the spray should entirely coalesce 

 into a coating, although where a second or third treatment is made 

 this often results. But there should be no spaces the size of one's 

 thumb nail not thoroughly peppered with the spray. (F. B. 243.) 



COPPER COMPOUNDS. 



Formulas for Bordeaux Mixture. The most valuable fungicide 

 for use in combating plant diseases is Bordeaux mixture, consisting 

 of a mixture of copper sulphate (bluestone) and stone lime slaked 

 in water. The formula varies somewhat according to the use which 

 is to be made of the spray. Following are the ones most used : 



Standard Bordeaux Mixture. The following formula, known 

 as the 6-4-50 formula, the ingredients being mentioned always in 

 the same order, is used in the preparation of the standard Bordeaux 

 mixture : 



Copper sulphate (bluestone) 6 pounds 



Lime 4 pounds 



Water to make 50 gallons 



This mixture can be used successfully on many plants, but on 

 others, like the peach and Japanese plum, it injures the foliage. It 

 also sometimes russets the fruits of apples and pears. It can be in- 

 creased in strength for certain purposes by reducing the proportion 

 of water, but the formula given above has been regarded as the stand- 

 ard with which all others should be compared, at least in experi- 

 mental work. 



The 5-5-50 Formula. Standard Bordeaux mixture is frequently 

 slightly modified, a very common modification being made according 

 to the formula which follows : 



Copper sulphate 5 pounds 



Lime 5 pounds 



Water to make 50 gallons 



The use of this formula is desirable where the purity of tho 

 lime is in doubt, as it makes certain, with lime of any reasonable 

 quality, that all of the copper is properly neutralized. The danger 

 of scorching or russeting the fruit is therefore less. Withholding 1 

 pound of copper sulphate also cheapens the mixture by a few cents. 

 For these reasons the 5-5-50 formula has come to be quite generally 

 used in orchard spraying. In fact, it has almost replaced (ho old 

 standard Bordeaux mixture in spraying for the apple scab. l>iUor- 

 rot, pear and cherry leaf-blight, and similar diseases. In the central 



