88 PHYSIOLOGICAL RELATIONS 



the following year applied with equal care the same mixture will 

 cause great injury or defoliation. Moreover, since the various para- 

 sitic fungi are differently affected by the strength as well as the 

 composition of the fungicide, it is important to know the specific 

 relations of each important parasitic organism. In the use of fun- 

 gicides there is a very large field of investigation possible because 

 of the fact that an intimate knowledge of the life histories of the 

 organisms concerned alone affords a proper index of the best time 

 for the application of the mixture, climatic conditions, and innu- 

 merable other factors, serving also to modify the requirements in 

 special cases. It has been possible to control very satisfactorily the 

 blight fungi of potato, most of the commoner grape parasites, the 

 bitter rot and scab of the apple, as well as numerous other diseases 

 by proper use of Bordeaux mixture. Nevertheless, Bordeaux mix- 

 ture should not be relied upon to the exclusion of other fungicides, 

 nor is the indiscriminate use of any fungicide to be generally 

 recommended. 



II. PREPARATION OF FUNGICIDES 



The more commonly employed of the many fungicides, which 

 have been used by practical growers and plant pathologists, are 

 as follows : Bordeaux mixture, ammoniacal copper carbonate, lime- 

 sulfur wash, potassium sulfide, flowers of sulfur, copper sulfate, 

 corrosive sublimate, and formalin. Of these preparations the 

 first five may be employed upon the foliage during the growing 

 condition of the plants. The remaining substances are generally 

 used for disinfection of seeds and plants in dormant or winter 

 condition. 



Bordeaux mixture. Bordeaux mixture is the most important 

 and the most commonly employed of fungicides. As a rule it 

 is true that Bordeaux mixture will protect a plant from fungous 

 attack where it is possible to protect it by means of any spray 

 mixture. Its injurious effects upon some plants preclude its 

 use. In other cases the discoloration of fruits immediately before 

 marketing would render them less desirable for market purposes, 

 and again the discoloration of the foliage makes it objectionable 

 in the case of ornamental plants. Bordeaux mixture may be used 

 also for plants in dormant condition. Under such circumstances 



