DOES WINTER KILL POTATO BLIGHT IN THE SOIL?* 



F. H. HALL. 



Rotation of crops is necessary to prevent trans- 

 Some plant mission of several plant diseases. Cabbage should 

 diseases not be planted the second year where the first 

 infect soils, season's crop has shown much clubroot, and pota- 

 toes should not follow potatoes where scab has 

 prevailed, nor where Fusarium wilt and its accompanying tuber 

 rot have been destructive. 



The most destructive potato disease in New York State, how- 

 ever, is late blight, with the common rot that follows it; and questions 

 relating to transmission and control of these troubles are exceedingly 

 important. Does this fungus survive the winter in the soil and 

 make a blighted field of one ye?r unsafe to use the next? 



Most authorities hold that the fungus causing 



Winter prob- these two troubles, Phytophthora infestans, does not 



ably destroys over-winter in the soil; and that there is no more 



Phytophthora. liability to blighting and rotting on a field thus 



affected the year before than on one free from the 



disease. Recently two authorities, one in England and one in 



America, have advanced the opposite view and advise against 



planting potatoes on soil where blight has been prevalent. 



To test the liability to such transmission, the 

 Station Station Botanist has carried on careful tests in two 

 tests. seasons; and finds no evidence that the fungus can 



survive the winter in the field, in central New York, 

 at least. In each of the tests, soil from a field of diseased potato 

 plants was thoroughly mixed, in boxes, with broken, rotten tubers 

 and pieces of blighted stems; and the boxes were exposed to the 

 weather during early winter. Later the boxes were brought into 

 the forcing house, a sound potato tuber was planted in each and 

 conditions made as favorable as possible for growth of plants and 

 development of the disease. In spite of warmth, abundant moisture, 

 both in the soil and in the air, and luxuriant, succulent growth of 

 the plants, not a sign of blighting appeared, even when the plants 

 were grown in a special glass chamber and thoroughly wet daily 

 with water drained from some of the soil mixed with diseased 

 material, or were painted with a thin mud made from such soil. 



The results, being negative, do not prove that the late-blight 

 fungus cannot remain alive over winter in the soil, but they make 

 such persistence appear highly improbable. 



It would seem unnecessary, then, to change the 



Depend on location of the potato crop to avoid this disease; 



spraying. especially as we know that thorough spraying will 



control both blight and rot and will increase the 



crop enough, taking one year with another, to make this a highly 



profitable regular practice in potato growing. 



The spraying of late potatoes should never be neglected. 



"Reprint of Popular Edition of Bulletin No. 367; see p. 180 for Bulletin. 



L7701 



