194 Diseases of Truck Crops 



Downy Mildew 

 Caused by Peronospora parasitica (Pers.) De By. 



Downy mildew, while a common field disease, 

 causes considerable damage to young seed l ings. 

 It is characterized by whitish downy patches on the 

 tmder side of the leaf. Seen from above, the af- 

 fected areas are angular, pale yellow, and somewhat 

 shrunken. The spots seem to be limited by the 

 veins of the leaf. The disease is common in damp 

 weather. Besides the cabbage, caiiliflower, radish, 

 turnips, and numerous other cruciferous hosts are 

 known to be susceptible to downy mildew. 



The sporophores of the fungus are stout and 

 numerously branched, each branch repeatedly forked. 

 The tips of the smaller branches are slender and 

 curved. The conidia are broadly elliptical, and the 

 resting spores are globose and smooth, becoming 

 wrinkled with age. 



In the seed bed or in the field, spraying with 

 4-4-50 Bordeaux will control the disease. The first 

 application should be given as soon as the disease 

 makes its appearance. Later the application will 

 be governed by weather conditions. 



Drop 



Caused by Sderotinia libertiana Fckl. 



Drop is a disease fairly common on cabbage. The 

 trouble may be recognized by a drooping and wilting 



