276 DISEASES OF TROPICAL PLANTS CH . 



history of the disease -organism, and the local climatic 

 conditions. Therefore, much depends upon the intel- 

 ligence and experience of the agriculturist. 



Only the most general rules for the use of fungicides 

 can be given in a work of this character. In warm, 

 moist climates and seasons, the applications should 

 usually be more frequent than where the humidity is 

 less. If there is any uncertainty as to the effect of the 

 fungicide on the plants, it should be tried on a very few 

 and the plants observe'd for 24 or 48 hours, before it is 

 used on the other plants. Some trees (peach) cannot 

 be sprayed with the ordinary fungicides while in foliage. 



FUNGICIDAL MIXTURES 



Bordeaux Mixture. This is one of the oldest and 

 best remedies, and is used more extensively than any 

 other. It derives its name from Bordeaux, France, 

 from whence it originated. The discovery of its im- 

 portance as a fungicide was due to an accident. It was 

 first used on grape vines in order to make petty thieves 

 think that the fruit had been poisoned, but it was soon 

 discovered that the vines on which it was used were 

 much healthier than those w^hich were not so treated. 

 It is a mixture of copper sulphate, lime, and water, in 

 which the copper sulphate is the real fungicide, the lime 

 being used to change the copper sulphate into a form 

 which will not be injurious to the host plant, and to 

 prevent the injurious effects of free copper sulphate ; 

 and the water is used as the solvent and carrier. The 

 proportions generally used are : 



Copper sulphate . . . 4 or 5 Ibs. 

 Unslaked lime ... 6 Ibs. 

 Water ..... 50 gallons. 



Put twenty-five gallons water in a barrel or other 

 suitable container, tie the copper sulphate in a bag, and 

 suspend just beneath the surface of the water and allow 

 to dissolve. Always use a wooden or brass vessel for 

 this purpose ; the copper sulphate will attack iron. 



