436 MANUAL OF FRUIT DISEASES 



same way, except that the amounts of copper-sulfate and lime 

 are varied according to the requirements. 



Copper-sulfate. 



This salt alone may be used only in very dilute solutions on 

 foliage and fruit, and as a summer spray has but few uses. 

 As a disinfectant for dormant peach trees it may be used as 

 strong as necessary and is very effective against peach leaf-curl. 



Copper-sulfate, 1 Ib. ; water, 15-25 gal. Dissolve the copper- 

 sulfate in the water. It is then ready for use. One pound 

 in twenty gallons of water has been found effective against 

 the above named disease. 



Lime-sulfur solution. 



The fungicidal value of lime-sulfur was discovered in America 

 about 1880 when California peach-growers using it on dormant 

 trees for the San Jose scale found that it controlled the leaf- 

 curl. As a matter of interest it may be noted that several 

 years earlier a boiled solution of lime and sulfur much diluted 

 was in use by European gardeners as a fungicide on growing 

 plants. Its use was, however, not general and its possibilities 

 were disregarded or overlooked in the general belief that the 

 newly discovered bordeaux mixture was of universal applica- 

 tion. The re-discovery of lime-sulfur as a summer spray about 

 1906 by Cordley of Oregon marks the beginning of a new epoch 

 in the history of fungicides. 



The fungicidal properties of lime-sulfur reside in the sulfur 

 or, more accurately perhaps, in the sulfuric acid which is even- 

 tually formed by the oxidation of the sulfur in the presence of 

 water. The special virtue of the lime-sulfur solution (poly- 

 sulfides of calcium) lies in the fact that after evaporation of the 

 water they are gradually oxidized, leaving pure sulfur in exceed- 

 ingly finely divided particles on the sprayed surface. Injury 

 by lime-sulfur usually occurs as the solution dries, and especially 

 where the trees have been drenched. Large quantities of the 

 solution are left along the curved edges of the leaves, where as 



