great loss from the late blight. Bordeaux mixture has proved to 

 be the best fungicide for potatoes, as it will not only effectively 

 control blights, but seems to have a stimulating effect upon the 

 vines. 



Early Blight. — This disease is caused by a fungus {Macro- 

 sporium solani) which attacks the leaves, producing dead round 

 spots marked with distinct concentric rings (Fig. 1). It appears in 

 July, usually before the late blight. In severe cases the leaves may 

 be largely killed. 



Late Blight. — This is perhaps the most destructive disease of 

 the potato in the northern part of the United States. It is caused 



by a fungus {Phytophthora infest- 

 ans) which attacks leaves, stems 

 and tubers. It is first noticeable 

 on the leaves as dark, watery 

 areas which later become brown 

 and dry. In cool, wet weather the 

 disease may spread with almost 

 phenomenal rapidity, killing the 

 vines, on which the dead leaves 

 hang shriveled and dry (Fig. 2). 

 Later the vines become prostrate. 

 From the diseased vines the 

 spores of the fungus fall upon 

 tlie soil and are washed in by the 

 rain, infecting the tubers. On 

 the tubers the disease takes the 

 form of a dry rot. On the outside 

 the affected areas are discolored 

 and become somewhat sunken 

 with age; beneath these areas the 

 flesh becomes reddish brown and 

 decays to a depth of not over a quarter of an inch (Fig. 3). In 

 storage this rot spreads among the tubers and may cause much 

 loss. 



In wet weather or on damp soil a watery rot is often associated 

 with this disease. This is due to })acteria which gain entrance from 

 the soil through the diseased spots. 



Fig. 2.— Late blight. (After New York 

 (General) Experiment Station Bulletin 

 No. 241.) 



