322 Minnesota Plant Diseases, 



celium, which feeds in a saprophytic manner upon vegetable 

 debris in the soil. After the mycelium has been strengthened 

 by this saprophytic life it is able to infect living plants. The 

 cucumber seems to suffer considerably but a large assembly of 

 other plants are also subject to the attack of either this or closely 

 allied species of fungi. The mycelium attacks the stem just 

 above the ground and the stem at this point is covered with a 

 fine white mold. The fungus proceeds rapidly up the stem and 

 the latter soon falls and dies. The mycelium now continues to 

 live in the dead tissues and builds up storage organs known as 

 sclerotia. These are small, dark, compact masses of fungus 

 threads in which a great amount of storage material such as 

 fungus starch is deposited. This sclerotium lives through the 

 winter in the dead stem and, in the spring time, produces a 

 cluster of cup-fungus fruiting bodies with long stalks. The in- 

 ner surface of the cup is lined with a palisade of sacs, each con- 

 taining eight spores. 



The fungus may also attack stored roots and bulbs such as 

 dahlias, turnips and beets and has been known to cause consid- 

 erable damage. Growing lettuce is also subject to attack and 

 the resulting disease is commonly known as drop from the rapid 

 collapse of the host plant. In this common disease the sum- 

 mer spores of the fungus are produced. All diseased plant 

 parts should be collected and burned. It has been recommend- 

 ed that lime be sprinkled on the soil to kill off the saprophytic 

 mycelium from which the infection takes place. The use of 

 fresh manure should be avoided where the disease has once 

 been found. Sterilizing of the soil has also proven successful in 

 controlling the sclerotium disease of lettuce. 



Drop of \ettuce (Sclerotinia libertiana FckL). See Diseases of 

 Greenhouse and Ornamental Plants. 



Red knot of currants [Nectria cinuabarina (Tode.) Fr.]. This 

 is not an uncommon disease in Minnesota. It attacks chiefly 

 the currant and often causes the death of the canes. The fruit- 

 ing bodies appear on the dead canes as small red buttons or 

 cushions which break through the bark of the cane. In an at- 

 tacked plant the foliage wilts and the fruit colors prematurely. 

 The fruit clusters of the currant are smaller than normal and 

 the berries fall off early. Sometimes only the central canes of 



