288 DINEASKS OF ECONOMIC PLANTS 



employ prcventi\'c spra3'S wlien the plants arc young. 

 Spraying tlic edible leaves as the plants approach maturity 

 injures the sale and is not permissible. 



Heterosporiose ' {Hclcrosporiuni variahile Cke.).- — This 

 disease was cspeciallj' injurious to spinach in eastern Vir- 

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

 noted in Connecticut. It apjiears early in January and 

 continues to increase until the spinach season is over. 

 Numerous leaf sjiots arc jiroduced, at first brown, later 

 sootj', as the conidiophores and conidia of the fungus de- 

 veloj). The older leaves usually show more injury than 

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

 The presence of tiic fungus lenders tlic leaves unsalable, and 

 much additional labor is required at harvest time to trim off 

 the injured leaves. 



The di.sea.se docs not seem (capable of attacking healthy, 

 vigorous plants, but usually follows injuries jiroduccd by 

 some other agencies. In Virginia it lias btMMi found to fol- 

 low the injuries ])ro(luced by perouospora. Injuries pro- 

 duced by cold weather, prolonged rains, in.sects, etc., un- 

 doubtedlj' afford weak points where infection may begin. 



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

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

 stroy all dead and diseased leaves, keeji the injuries from 

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

 much as pos.sible. 



Downy mildew (Perouospora cffusa (Grev.) llbh.). — 

 Gray to slightly violet, downy s|)ots upon the lower sur- 

 faces of leaves, accomjianicd by jiale yellow spots upon the 



' This description was prcprircd at tlic rcriuest of the authors by H. S. 

 Heed. 



