328 



Minnesota Plant Diseases. 



The leaf blight of celery (Ccrcospora apii Fr.). The fungus 



causing this disease is a loose 



spored, imperfect fungus. It 



causes the formation of red- 

 dish to brownish spots on the 



leaves, which may spread and 



increase in size until the leaf is 



seriously injured. The fungus 



thrives well on plants in dry 



situations and is particularly 



effective against young plants. 



When badly affected the leaf 



turns yellow and finally brown. 



Spots may also appear on the 



stem. The spores arise from 



upright fungus-threads in the 



center of the spot and are ar- 

 ranged in a fine, loose, mold- 

 like growth. Shade and moist 



situations have been recom- 

 mended, but are only partially 



successful. Spraying will also 



keep the fungus in check. 

 The spraying should com- 

 mence early and bordeaux may be used at first but the ammo- 

 niacal copper carbonate is used in the later sprayings. 



The leaf spot of beets (Ccrcospora bcticola Sacc.). This is a 

 common spot disease on the leaves of the beet. The cause of 

 the disease is a loose-spored imperfect fungus. It forms small 

 circular spots on the leaves, often in great abundance. The 

 spots have a purple border and whitish centers, where the 

 loosely arranged threads bearing the spores are found. 



Spraying with bordeaux mixture has been recommended. 

 Frequent applications should be made throughout the growing 

 season. 



Black rot of tomato (Macrosporium tomato Cooke). Tlrs 

 fungus attacks chiefly the fruits but is also found on the leaves 

 and stems. It is probably identical with the fungus of early 

 potato blight. It forms on the fruit circular spots, under which 



FIG. 165. Aiithracnose of bean. After Hal- 

 sted. 



