POTATO WILT, LEAF-EOLL, AND RELATED DISEASES. 11 



greatly reducing our yields, has beeu entirely overlooked. The seed potatoes through- 

 out Ohio are infected to a much greater extent than would have been supposed. This 

 indicates that much of our potato land is already carrying the fungus to a greater or 

 less amount, and as a result our yields are probably being reduced considerably. 

 (Manns, 1911.) 



The writer has found many Michigan fields infected with wilt. 

 The original material studied by Dr. Erwin F. Smith also came from 

 this State. In Illinois and southern Wisconsin and in Minnesota 

 wilt appears to be present in the older communities, where potatoes 

 have long been grown, but in the newer districts of Wisconsin and 

 Minnesota the growers still have an opportunity to protect themselves 

 against this danger. 



There are important potato districts in western Nebraska where 

 Fusarium wilt occins, although the leaf-roll and the powdery dry-rot 

 (Fusarium trichothecioides) are also factors there. (Orton, 1913.) 

 All the older irrigated districts of the West are infected, and the newer 

 ones are rapidly becoming so, with the possible exception of the higher 

 and cooler valleys, concerning which definite information is lacking at 

 present. The wilt has been long present in Colorado and caused much 

 injury, especially when attempts were made to grow two or three 

 successive crops of potatoes. In Utah it is much the same, and the 

 newly opened districts in Idaho are rapidly introducing the fungus 

 in seed potatoes brought from older localities. Nor is the wilt con- 

 fined to the irrigated parts of the West. It also occurs on the "dry 

 farms," and is not the least of the problems which the settlers in these 

 areas have to solve. The potatoes at the- field station of the Bureau 

 of Plant Industry at Akron, Colo., have been attacked by wilt for 

 several years and the jdeld much diminished. 



It is, however, in potato growing under irrigation that wilt plays 

 the largest r6le. These lands are all high priced, from $200 an acre 

 up. The farmer has to carry fixed charges in the way of interest, 

 water rents, irrigation bonds, and the like that make it necessary 

 for him to grow a crop more remunerative than grain or alfalfa. 

 Sugar beets and potatoes are, in most cases, the only crops that 

 answer this requirement in these districts. The farmers naturally 

 desire to grow potatoes as frequently as possible, but are prevented 

 from doing so by the wilt, which forces a rotation. 



In California wilt is the principal factor limiting the production of 

 potatoes in the famous delta district of the San Joaquin Valley 

 (Orton, 1909). Here the reclaimed moor, or tul.e, soils are won- 

 derfully productive when first planted, but the yield of potatoes falls 

 off with each succeeding crop until very small yields are secured 

 unless rotations with barley or other crops are practiced. The 

 potatoes from these diseased fields show almost universal infection 

 with Fusarium oxysporum, which is there the principal, if not the 



