POTATO DISEASES 



JL 4 JLw 



1904. Report Connecticut Experiment 

 Station, 1903. 



1907. Wasliington Experiment Station 

 Bulletin 87. 



1909. U. S. Department of Agriculture, 

 Bureau of Plant Industry, Circular 23. 



1910, Ohio Experiment Station Bulle- 

 tin 214. 



**1911. Ohio Experiment Station Bul- 

 letin 299. 



**1912. Wisconsin Experiment Station 

 Circular 36. 



1912. Journal Washington Academy of 

 Science, Vol. II, No. 6. 



**1913. Nebraska Research Bulletin 1. 



**1913. Nebraska Bulletin 134. 



**Phytopathology, Vol. Ill, No. 1. 



Internal Brown Rot 



Internal brown rot is the name given 

 to a disease which has recently appeared 

 in a few potato-growing sections of this 

 country. It is first noticed by the dark- 

 ening more or less of the starchy portion 

 of the tubers, without any manifestation 

 of its presence on the outside; later on 

 the potato rots. The life history of this 

 disease is not known, nor are any 

 remedies known for it. Ordinary pru- 

 dence, however, would indicate that seed 

 potatoes in the least affected with this 

 trouble should not be planted. 



Early Blight 



AUernaria solani (B. & M.) Jones & Grant 

 Early blight of potato is a premature 

 spotting and dying of the potato leaves, 

 due to the work of a parasitic fungus. 

 The occurrence of the early blight is li- 

 able to be influenced by the general vigor 

 and other conditions of the plant; yet 

 there is no just basis for denying, in the 

 light of our present knowledge, the 

 parasitic nature of this disease. Jones 

 has made cultures of the fungus and pro- 

 duced the disease by inoculation (Ver- 

 mont Experiment Station Bulletins 24 and 

 28; Report 1892) and has secured most 

 admirable results by the use of fungicides. 

 This successful spraying in itself is in 

 the nature of proof of parasitic character. 



Control 



Spray thoroughly with Bordeaux mix- 

 ture, adding arsenites for the insects, as 

 required. 



There is real danger of the confusion 

 of early blight with the Fusarium blight 

 described elsewhere in this section. 



Late Blight of Potatoes 



Phytophthora infestans 

 P. D. Bailey 



The disease of potatoes commonly 

 known as late blight or downy mildew is 

 almost universal in extent and has caused 

 more loss than all the other pests of this 

 crop combined. In New York state it 

 has caused a loss of $10,000,000 in one 

 year and an estimate for the United 

 States places an annual loss at $36,000,000. 



The outbreak of blight in Ireland in 

 1845 is often spoken of as the starting 

 point, but, as a matter of fact, records 

 show that it originated in Chili, the home 

 of the potato, and was introduced into the 

 United States, near Boston, as early as 

 1840. In Australia and Tasmania the in- 

 vasion has been more recent, probably in 

 the present century. 



In the Northwest we have no record to 

 show when the disease first appeared. 

 It is certain that it has appeared occa- 

 sionally in the coast region for years. 

 The season of 1912 was unusually favor- 

 able to it and the fungus rapidly spread 

 and damaged late potatoes throughout 

 the lower Columbia and Coast region. 

 The large acreage planted made the loss 

 in some cases quite serious. 



Symptoms 



The leaves are the first point of attack 

 when the disease is spreading in the field. 

 Spots appear on any part, more often 

 near the tip or margin; these affected 

 areas spread rapidly until the entire leaf 

 is blackened and dead. As the spot 

 spreads, the margin is changed to a light 

 green and is watery in appearance, often 

 a fine white down can be seen, generally 

 on the lower surface. Drought or unfav- 

 orable temperature will check the growth 

 of the fungus, but if the mean daily 

 temperature ranges between 70 degrees 



