6 



The Bulletin. 



that of a cowpea. These bodies are called sclerotia, and are the most 

 distinctive indication of this disease. A less serious root rot of clovers, 

 caused by the fungus Rhizoctonia, may show similar general symptoms, 

 but the sclerotia are lacking. 



Cause. — The cause of this disease is a fungus, Sclerotinia, that 

 may live over in the soil on decaying vegetable material from one 

 season to the next. The sclerotia are particularly adapted for with- 

 standing extremes of temperature and moisture and on the return of 

 favorable conditions may start the disease. The disease has only 

 recently begun to be serious in the United States. It is closely similar 

 to the wilt or drop of lettuce. 



Fig. 1. Stem Rot of Clover. Slightly affected plant on the left, badly affected one on the right. 

 Note sclerotia on stem in the middle; one is just above the head of the arrow and another 

 smaller, round one is in line with the arrow art the center. 



Dissemination. — The smallest of the sclerotia are about the size of 

 clover seeds and are not removed in the usual processes of cleaning. A 

 few of these may start the disease in a field. It will spread gradually 

 from these centers by growth of the fungous threads to neighboring 

 plants, causing a slow but progressive enlargement of affected areas. 

 Preparation of the soil for later crops will distribute the infective 

 material up and down the rows, and there is danger of a large increase 

 the second and third years, if susceptible crops are grown on the land. 

 Any transfer of infected soil would serve to spread this disease, either 

 through washing by water or through the agency of farm implements 

 or stock. In using soil for inoculation of leguminous crops with tuber- 



