Family Cruciferae 209 



radishes are useless for the market. The disease 

 seldom attacks the red or the black-skimied varieties. 

 For further consideration of black rot see p. 190. 



Scab 



Caused by Actinomyces chromogenus Gasp. 



Scab is not a common field disease of radishes. It 

 is, however, found to be troublesome on the crop 

 grown in greenhouses. The French Breakfast is 

 commonly susceptible to the disease. The trouble 

 may be expected if the crop is planted in a soil which 

 previously produced a potato crop that was badly 

 scabbed or where infected manure was used, or too 

 much lime applied. For further description of scab, 

 see p. 317. 



Damping Off 



Caused by Rheosporangium aphanidermatum Ed. 



This disease, which was studied and described by 

 Edson,^ is very troublesome, attacking radish and 

 beet seedlings alike. 



Symptoms. The disease is confined to the root 

 system, seldom appearing above ground. Diseased 

 plants have a flabby appearance, and the normal green 

 of the foliage is displaced by a slightly yellowish tinge. 



« Edson, H. A., U. S. Dept. of Agr., Jour. Agr. Research, 4: 279- 



292. 1915- 

 14 



