288 DISEASES OF ECONOMIC PLANTS 



employ preventive sprays when the plants are young. 

 Spraying the edible leaves as the plants approach maturity 

 injures the sale and is not permissible. 



Heterosporiose ^ (Heterosporium variahile Cke.). — This 

 disease was especially injurious to spinach in eastern Vir- 

 ginia during the winter of 1908-1909, and has also been 

 noted in Connecticut. It appears early in January and 

 continues to increase until the spinach season is over. 

 Numerous leaf spots are produced, at first brown, later 

 sooty, as the conidiophores and conidia of the fungus de- 

 velop. The older leaves usually show more injurj^ than 

 the younger, but at times all leaves are seriously affected. 

 The presence of the fungus renders the leaves unsalable, and 

 much additional labor is required at harvest time to trim off 

 the injured leaves. 



The disease does not seem capable of attacking healthy, 

 vigorous plants, but usually follows injuries produced by 

 some other agencies. In Virginia it has been found to fol- 

 low the injuries produced by peronospora. Injuries pro- 

 duced by cold weather, prolonged rains, insects, etc., un- 

 doubtedly afford weak points where infection may begin. 



The best preventive measures, so far as known at present, 

 are to follow general hygienic precautions, rake up and de- 

 stroy all dead and diseased leaves, keep the injuries from 

 insects and other fungi at a minimum, and rotate crops as 

 much as possible. 



Downy mildew {Peronospora effusa (Grev.) Rbh.). — 

 Gray to slightly violet, downy spots upon the lower sur- 

 faces of leaves, accompanied by pale yellow spots upon the 



^ This description was prepared at the request of the authors by H. S. 

 Reed. 



