78 



Diseases of Economic Plants 



vents either the growth of the seeching or successful budding 

 or grafting. 



On old leaves, though often abundant, the fungus does not 

 cause great damage, but when the attack is made on young 

 growing tips, or on young leaves, these delicate structures 

 suffer greatly from loss of nourishment. The disease is com- 

 mon from the Atlantic to the Pacific. 



Unlike most fungi the mildew grows best during fair, 

 diy weather. A light rain, which spreads the spores and 

 furnishes sufficient moisture for germi- 

 nation, followed by a dry spell, best 

 favors the development of powdery- 

 mildew. 



The use of Bordeaux mixture, sulfur 

 dust, or lime-sulfur has proved satisfac- 

 tory. Apply about every ten days dur- 

 ing the early growing season; more 

 frequently, if necessary to replace the 

 poison washed off by rain. 



' Wood-rot ^ (Schizophyllum alneurn 

 (L.) Schr.). — Small white specks, the 

 sporophores, appear upon the limbs 

 and trunk in early summer. In the 

 autumn they are well developed and 

 abundant ; white and very hairy, 1-3 cm. 

 in diameter, usually attached on one 

 side with the margins incurved. The 

 gills are white, woolly, branched, deeply 

 split along the edge, and revolute. 

 The affected wood is brittle and pene- 

 trated by black lines. Apparently this disease starts in roots 

 injured by tools during cultivation or in wounds upon limbs. 



Fig. 39. — Schizo- 

 phyllum alneum, 

 frequently the 

 causal fungus of 

 wood-rot of cherry 

 and other trees. 

 After Atkinson. 



Minor diseases 



Die-back ^^ {Vaha leucostoma, Cystospora). — The discus- 

 sion of (lie-back on p. 86 is applicable in this connection. 

 The disease is conniion on the cherry in the United States 



