1 68 Diseases of Truck Crops 



sparingly from this growth when in contact with the 

 decayed tissue, but very abundantly on that part of 

 the mycelium which has spread over the healthy sur- 

 face or into the glass or filter paper of the moist cham- 

 ber. Trichoderma lignorum is common and widely 

 distributed on decaying wood and various other sub- 

 stances. Trichoderma Koningi was originally iso- 

 lated from the soil by Oudemans and is still looked 

 upon as a soil organism. The spores are elliptical and 

 are borne on characteristic conidiophores (fig. 28 p). 



Soil Stain or Scurf 



Caused by Monilochaetes infuscans E. and E. 



Soil stain is not a disease to be feared in the sense 

 that it may produce a direct rot in the mature roots. 

 Nevertheless, it is economically important. Growers 

 whose lands are badly infected assert that stained 

 roots keep better in storage. Others find consolation 

 in saying, "There is no such thing as stain, the dark 

 color of the skin being merely a varietal character- 

 istic." The fact remains, however, that many 

 Eastern markets discriminate against stained roots. 

 In years of over-production the New York market 

 refuses stained roots altogether. The Western buy- 

 ers, on the contrary, are lax on this point; other- 

 wise, many growers in the United States would be 

 forced to cease producing sweet potatoes for want 

 of a market, since soil stain is prevalent on practi- 

 cally all sweet-potato land. 



Symptoms. Soil stain is characterized at first by 

 small, circular, deep clay-colored spots on the surface 



