DISEASES OF ECONOMIC PLANTS 



fungi have been isolated 

 from these spots/ some 

 of them may sustain a 

 causal relation to the 

 disease. 



Whatever the actual 

 causal fungus may be, 

 these spots are all, or 

 nearly all, of fungous ori- 

 gin and are amenable to 

 preventive spraying with 

 Bordeaux mixture. The 

 first of three or four 

 appUcations should be 

 given with the opening 

 of the leaf buds. 



Illosporiose, leaf spot 

 (Illosporium malijolio- 

 rum Shel.). — This is 

 said by Sheldon- to be 

 the cause of much of the 

 defoliation of apple or- 

 chards in West Virginia 

 and adjacent states. 

 The spots are circular, 

 5-15 mm. in diameter, brown or mottled and gray, con- 

 centrically marked. 

 For treatment see page 100. 



' Notably by Hartly, Minnesota, and by Lewis, I. M., New Hampshire 

 Agr. Exp. Sta. Rpt. 1&-20, November, 1908. 

 " Sheldon, J. L., Torreya, S, 141, June, 1908. 



Fig. 33. — .\pple leaf spot in late stage of 

 development, showing concentric rings. 

 Original. 



