Minnesota Plant Diseases. 339 



thrives best in a moist atmosphere and damp situations, hence 

 is often luxuriant in greenhouses. Infected plants are stunted 

 and turn pale yellowish in color. 



"This disease is kept in check by subirrigation or care in 

 watering and ventilating to keep plants and atmosphere as free 

 from moisture as is consistent with good growth." (Conn. Ex. 

 Sta. Bull. 142 — 1903.) It has been recommended that infected 

 frames and houses be abandoned for lettuce culture at least for a 

 time. 



The downy mildew of beets (Peronospora schachtii Fckl.). 

 This disease may prove a serious pest in the raising of beets. 

 The fungus attacks chiefly the inner leaves and in seedling 

 plants may cause the death of the plant. The spore patches 

 are on the under sides of the inner leaves and are greyish, mold- 

 like patches. The fungus threads are said to be able to live 

 through the winter in the roots. 



The infected plants should be burned. Rotation of crops 

 has been recommended in order to give the mycelium in the 

 roots a chance to die out. 



The downy mildew of spinach [Peronospora eifusa (Grev.) 

 Rabh.]. Spinach and the other plants of the goosefoot family 

 are frequently attacked by a downy mildew which may cause 

 serious damage. It is also found on wild plants of the same 

 family. The mold patches of summer spores are found on the 

 lower surface of the leaf and are greyish lilac in color. The 

 winter spores are similar to those of downy mildew of clover. 



The diseased plant should be burned to prevent the spread 

 of the disease and its recurrence in the following year. 



Downy mildew of clovers. See Diseases of Field and Forage 



Crops. 



Downy mildew of violet (Peronospora violae DeBy.). See 

 Diseases of Greenhouse and Ornamental Plants. 



Damping-off of seedlings {Pythium debaryanum Hesse.). 

 See Diseases of Greenhouse and Ornamental Plants. 



The seedling disease of cabbages [Olpidium brassicae (Wor.) 

 Daug.]. This disease is probably not serious in Minnesota. It 

 attacks seedling cabbages and causes a dropping of the plant 

 by the death of the stem. The fungus belongs to a very low or- 

 der of algal fungi and consists of a single cell which invades the 



