116 MANUAL OF FRUIT DISEASES 



and soon the parasite has extended itself to other twigs and 

 leaves in a manner conducive to certain perpetuation. 



Control. 



The application of certain fungicides -supplemented by the 

 eradication of heavily mildewed twigs are satisfactory remedial 

 measures. But the disease is not easy to control. In those 

 cases where copper sprays are still in use, little benefit may be 

 expected so far as the control of apple powdery-mildew is con- 

 cerned. The chief difficulties lie in the fact that copper com- 

 pounds produce leaf and fruit injury, and that the mildew fungus 

 is not as susceptible to bordeaux mixture and similar copper 

 sprays as it is to the sulfur sprays. The sulfur compounds are 

 effective under certain conditions of preparation. Sulfur in 

 some very finely divided state is the most efficient fungicide 

 available for use against this disease. Such fungicides as ground 

 sulfur, sulfur flour and flowers of sulfur are all said to be too 

 coarse to yield satisfactory results. On the other hand, pre- 

 cipitated sulfur is particularly effective against apple powdery- 

 mildew. This may be obtained by the use of lime-sulfur solu- 

 tion, diluted one gallon of the concentrated solution to fifty 

 gallons of water to which is added three pounds of iron-sulfate. 

 By stirring the two together a black, muddy precipitate is 

 formed ; this contains sulfur in a finely divided condition, iron- 

 sulfid and calcium-sulfate. It has been demonstrated that this 

 spray is effective against apple-mildew both in New York State 

 and in the Pajaro Valley, California. In the nursery the first 

 application should be made soon after the seedlings have 

 developed the first new shoots. Three or four sprayings should 

 follow at intervals of about two weeks. According to experi- 

 ence in the Pajaro Valley, orchard trees should be sprayed as 

 follows : (1) apply the above fungicide in conjunction with the 

 first spraying for codlin-moth ; (2) in con j unction with the second 

 application for codlin-moth ; (3) three weeks after the second ; 

 (4) three weeks after the third. These recommendations, while 



