1718 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



Kil)1i<ii;rsii>li.v 



1906. Vermont Agricultural Experi- 

 ment Station Bulletin 119. 



1908. Wisconsin Agricultural E.xperi- 

 ment Station Bulletin 168. 



1911. New York Agricultural Experi- 

 ment Station Bulletin 338. 



1912. New York (Geneva) Agricul- 

 tural Experiment Station Bulletin 349. 



1912. New York (Geneva) Agricul- 

 tural Experiment Station Bulletin 352. 



1912. Vermont Agricultural Experi- 

 ment Station Bulletin 162. 



1912. U. S. Department of Agriculture, 

 Bureau of Plant Industry Bulletin 245. 



Dors AVintcr Kill Potato Blifrht in tlie 

 SoiU 



♦Rotation of crops is necessary to pre- 

 vent transmission of several plant dis- 

 eases. Cabbage should not be planted the 

 second year where the first season's crop 

 has shown much clubroot, and potatoes 

 should not follow potatoes where scab has 

 prevailed, nor where Fusarium wilt and 

 its accompanying tuber rot have been de- 

 structive. 



The most destructive potato disease, 

 however, 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 year un- 

 safe to use the next? 

 Winter Probahly Destroys Phytoplitliora 



Most authorities hold that the fungus 

 causing these two troubles, Phytuphtora 

 infestans, does not over-winter in the 

 soil: and that there is no more liability 

 to blighting and rotting on a field thus 

 affected the year before than on one free 

 from the disease. Recently two authori- 

 ties, one in England and one in America, 

 have advanced the oi)posite view and ad- 

 vise against planting potatoes on soil 

 where blight has been prevalent. 



To test the liability to such transmis- 

 sion, the station botanist at Geneva, N. 

 y., has carried on careful tests in two 

 seasons; and finds no evidence that the 

 fungus can survive the winter in the 



•Geneva (N. Y.) Bulletin .367. 



field in Central New York at least. In 

 each of the tests, soil from a field of dis- 

 eased 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 pos- 

 sible for growth of plants and develop- 

 ment 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 blight- 

 ing 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. 



Depend on Spraying 



It would seem unnecessary, then, to 

 change the location of the potato crop to 

 avoid this disease; 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 prac- 

 tice in potato growing. 



The spraying of late potatoes shoirid 

 never be neglected. 



Leaf Blotch 



Cercospora concors 



Appears in some of the New England 

 states, but does not appear to be serious. 



Leaf Curl. See Leaf Blotch, this sec- 

 tion. 



Leaf Roll 



As indicated by the name, leaf roll is 

 marked by an upward rolling of the 

 leaves on their midrib. There is usually 

 a pronounced change in the color of the 

 foliage to a yellow, unhealthy shade, of- 

 ten tinged reddish or pur])lish. 



The disease may start early in summer 

 and be far advanced by the end of July. 



