Rural School Leaflet 



919 



brought about the Irish famine of 1846. Much was written about the 

 disease at that time and its cause was correctly determined. Other 

 epidemics have occurred at intervals since. The loss from this disease 

 in New York State alone during the three years from 1903 to 1905 is 

 estimated at $40,000,000. The disease is now to be found in all humid 



climates where potatoes ^ 



are grown, but the j 



fungus that causes the -■ • 



disease does not thrive 

 well except in temperate 

 ^regions. 



Symptoms. — O n the 

 leaves the first signs of 

 disease are leaf spots 

 having a water-soaked 

 appearance. This is par- 

 ticularly noticeable when 

 the affected leaf is held 

 to the light. Later this 

 spot blackens and dries, 

 but often a water-soaked 

 area at the margin 

 indicates the continued 

 activity of the fungus. 

 These spots have an 

 indefinite margin and 

 are one half inch or more 

 in diameter, sometimes 

 involving the entire leaf 

 and leaf stem. On the 

 underside of the spot 

 may be noticed a moldy 

 or mildewy growth. 

 This may serve to 

 distinguish the downy 

 leaf. 



On the stems, watery spots develop which later turn browfi or black 

 and become dry. The foliage beyond the affected area then dies from 

 lack of moistiire. 



On the tubers, the lesions when first noticeable are small discolored 

 spots not so large as the end of one's finger. If the skin of the tuber is 

 scraped away at this point, a reddish brown color, characteristic of the 



Potato vine killed, by the downy mildew 

 (After Geneva Bui. 241, Plate X) 



mildew from other spot diseases of the 



