SWEET PEA DISEASES AND THEIR CONTROL 133 



in the house. In places where this disease has made its appearance 

 the growing of greenhouse sweet peas had to be abandoned within 

 less than two years. The disease produces a sudden flagging of the 

 leaves which is accompanied by a wilting and collapse of the 

 seedlings. Usually, upon sowing the seed, a fair percentage germi- 

 nate and reach the height of about eight to ten inches, when they 

 are attacked by the fungus. If the collapsed seedlings are allowed 

 to remain on the ground, the dead stems will soon be covered with 

 the sickle-shaped spores of the Fusarium fungus. Eventually the 

 dead tissue rots, attracting small fruit flies which now begin to dis- 

 tribute the spores to different places in the same house. The 

 trouble usually manifests itself in widely separated spots on the 

 bench. These spots, however, quickly spread, involving the entire 

 bed, which may suddenly assume a wilted appearance. Here and 

 there, however, and in the same bench, a few plants remain alive 

 and keep on growing in spite of the disease. 



Stem or Collar rot, Sclerotinia libertiana Fckl. 



This is usually a seedling disease, although it may attack plants 

 of all ages. Like the Rhizoctonia rot it attacks many different 

 kinds of seedlings. The trouble is most severe in houses poorly 

 ventilated and in beds over-watered or lacking proper drainage; 

 and in damp places out-of-doors. The disease spreads very quickly 

 and is soon fatal. iVffected plants first show a wilting of the tip 

 and flagging of the leaves, and then the seedlings fall over and col- 

 lapse. The cause of this disease is a fungus (Sclerotinia libertiana 

 Fckl.), which also causes a drop disease of lettuce and of other 

 plants. The fungus does not seem to attack the roots, but pene- 

 trates the collar of the stem and completely invades the vessels, 

 thus clogging the upward flow of the water from the roots to the 

 stem. Freshl}^ collapsed plants usually have a water-soaked 

 appearance, and are later overrun by a white weft, which is merely 

 the mycelium of the fungus; this is followed by sclerotia (resting 

 bodies), which are found scattered here and there on or within the 

 affected stems. The fungus is a soil organism which occasionally 

 causes trouble in clover fields. It is introduced with animal 



