Vegetable and Field Crops 



171 



and radish it may be recognized by the cotton-like myceHum 

 and the black sclerotia which appear in advanced stages of 

 disease. It is particularly troublesome in the Southern 

 states. 



A form of this rot is described by Hedgcock as closely 

 resembhng black-rot, except that it is more watery. Often, 

 too, the petioles rot away 

 at the base and the leaves 

 droop. The general prac- 

 tices recommended under 

 lettuce drop will apply. 



Downy-mildew (Pe)-- 

 onospora 'parasitica (Pers.) 

 De Bary). — Downy-mil- 

 dew produces the char- 

 acteristic downy patches 

 of sporophores upon the 

 lower surface of the leaves, 

 much as is the case of the 

 grape. Seen from above 

 the diseased spots are an- 

 gular, limited by the veins, 

 pale yellow, and the tissue 

 is somewhat shrunken. 



The disease is common 

 to cabbage, collard, cauli- 

 flower, turnip, radish, and 

 many other members of 

 the cress family. It has 

 been reported in several 

 states, notably Ohio, New Jerse}^ New York, Delaware, 

 Maryland, South Carolina, North Carolina, West Virginia, 

 and in Europe and Australia. Though it is seldom of impor- 

 tance in the field, it occasionally does damage in the seed bed. 



Spraying the plants in the seed bed with Bordeaux mix- 

 ture will hold the disease in check. Diseased plants should 

 be destroyed by fire as soon as the bed has been used. 



Fig. 93. — ■ Seedling cabl)age plant 

 spotted with downy-mildew. 

 Original. 



