Vegetable and Field Crops 257 



one root or more may be diseased; in later stages all 

 succumb. 



In a series of rotation tests, planned and inaugurated by 

 the author, ^^^ it was found that growing corn, wheat, cow- 

 peas, clover, and mixed grasses, either singly or in rotation for 

 a period of five years on badly diseased soil, reduced the loss 

 from wilt to an almost negligible quantity. 



The means by which this disease spreads from field to 

 field, and methods to prevent such spreading, are adequately 

 discussed under soil diseases, p. 26. 



A similar wilt, but due to a Fusarium, has been reported 

 from Maryland. 



Wildfire ^""^^ ""'' {Pseudomonas tabacum (W. & F.)). — 

 A bacterial leaf-spot, first noticed in 1917, is widespread 

 in North Carolina, Virginia, and occurs also in Wiscon- 

 sin. Loss of $100 per acre for entire crops is commonly 

 reported. The spot is 2-3 cm. in diameter, often concen- 

 trically marked, and has a translucent border surrounded bj' a 

 chlorotic halo. Another bacterial leaf-spot known as An- 

 gular leaf-spot (Ps. angulatum (F. & M.)) was also described 

 in 1917 as destructive in Virginia. The spots are angular and 

 are not surrounded by the halo common in "wildfire." 



Leaf-spot ''*°^ {Cercospora nicotiance E. & E.). — This dis- 

 ease, most abundant upon the lower leaves, appears as brown, 

 circular spots from the size of a pinhead to a centimeter or 

 more in diameter. Older spots bear white centers bordered by 

 a darker, raised line, and the centers often fall away, leaving ir- 

 regular holes. The whole leaf yellows and ripens prematurely. 



The disease was first described by Sturgis from specimens 

 sent from South Carolina, where it was destructive, prac- 

 tically ruining the crop. A damage of SIOOO to one crop 

 alone was noted. The use of Bordeaux mixture early in the 

 season is permissible and advantageous. 



Bed-rot iCorticium vagum) . — Damping-off and rot of 

 seedlings occur in the seed bed. The causal fungus may often 

 be seen as spots of web-like white mold upon the ground 

 around the affected plants. The general characters and 



