POWDERY SCAB OF POTATOES. 9 



might make it a serious enemy of the potato in the United States, at 

 least as bad as the common scab caused by Oospora scabies, and prob- 

 ably worse. 



The effect of the milder form of Spongospora upon the tuber resem- 

 bles that of the common scab in that it disfigures the potato and 

 thereby reduces the market price, even though the food value may 

 not be materially impaired. It differs from Oospora scab in that the 

 advanced or cankerous stage ruins the tuber for both table and seed 

 purposes. 



In this connection it should be remembered that any kind of scab 

 or other injury that mars or defaces the potato tuber is a more serious 

 handicap in the American markets than in those of some European 

 countries, due to the fact that consumers abroad offer fewer objec- 

 tions to scabby potatoes than consumers in the United States. There 

 is even a belief prevalent abroad that scabbiness is an indication of 

 superior quality. In the United States, when potatoes are put on 

 the market, scabby potatoes must be sorted out, and therefore are 

 of no use except for stock feed or the manufacture of starch. In 

 Maine the price of scabby potatoes in the autumn of 1913 was 50 

 cents per barrel, while clean stock brought $1.50 per barrel. In the 

 country as a whole, hundreds of thousands of bushels of potatoes are 

 left in the fields because they are too scabby to market. There are 

 frequent instances in the New York markets, according to potato 

 dealers, where carload consignments are rejected because of the 

 presence of numerous scabby potatoes. When the soil becomes in- 

 fested with scab its value as potato land materially depreciates. This 

 is especially true in sections where potatoes constitute the chief crop. 



The character and relationship of the parasite should also be 

 taken into consideration in judging the danger which powdery scab 

 presents. This is a ^ase of dealing with a slinie mold, a relative of 

 the serious disease of cabbage, turnips, and related plants, known as 

 clubroot. 



If powdery scab should prove no more troublesome in the United 

 States than it has been up to the present in Europe, it would be rated 

 as a disease of secondary importance as compared with late-blight or 

 with Fusarium wilt. But there are reasons for fearing that it may 

 become more prevalent here. It seems to be a fact that common scab 

 is less troublesome in Europe than in America, and the same condition 

 might be the case with powdery scab. It quite often occurs that 

 introduced parasites are more destructive in a new habitat than in 

 their native environment. Likewise, it is not impossible that Spon- 

 gospora may find the American varieties of potatoes more sus- 

 ceptible than the European sorts. There is also no means of pre- 

 dicting the behavior of Spongospora under the varied climatic and 

 soil conditions of the several States. The parasite has only recently 



