Plant Diseases 



431 



is the cutting and immediate burning of all infected branches. 

 These branches should be cut well below the darkened portions, 

 because the bacteria usually extend some distance down the water- 

 conducting tissues. Care must also be exercised in keeping the 

 knife or saw from coming in contact with the diseased portion of 

 the branches. Cankers on the older branches should be cut out 

 during the fall or winter to prevent infection the following season. 

 Damping off of seedlings. Gardeners and nurserymen are 

 much troubled by the damping off of seedlings in seedbeds. 

 The fungi concerned in this process occur in the soil, and some 

 are related to the common bread mold. The seedlings when 

 first attacked become transparent, fall to the ground, die, and 

 are finally consumed by the fungus. These fungi reproduce by 

 spores, some of which are thick-walled and carry the plant over 

 winter in the soil. Damping off may be controlled by sterilizing 

 the soil of seedbeds. This may be accomplished by treating the 

 soil with a 10 per cent solution of formalin and covering the bed 

 with a piece of oilcloth for 24 hours. 



A. B. Stout 



Fig. 268. Damping off of seedling lettuce. This disease is due to molds and other fungi 

 that attack the stems at the surface of the soil and cause the seedlings to rot. 



