12 BULLETIN 64, U. S. DEPAETMENT OF AGEICULTURE. 



sole, cause of the early maturity and diminished harvests. This tule 

 land for potatoes commands a cash rental of $20 to $25, while for 

 barle}' growing only $8 to $12 is paid, but after the second crop of 

 potatoes the less profitable crop must intervene (Irish, 1913). 



One of the leading potato districts north of California is the Willa- 

 mette Valley, in Oregon. Here wilt is present to a serious extent. 

 During visits in 1909 and 1910 the writer saw fields liberally dotted 

 with yellow and dying plants. This valley furnishes most of the 

 seed i^otatoes brought into California, and inspection of such potatoes 

 has revealed much stem-ejid browning. 



It is certain that the Fusarium wilt is a nation-wide problem and 

 one that will have a marked influence upon American agriculture. 

 At present it causes losses which probably run into millions of dollars ; 

 but, if in the end the growers are forced to adopt better rotation 

 systems, who shall say that the final influence of this disease factor 

 may not be beneficial ? 



Estimates of the money losses from Fusarium wilt must be largely 

 speculative, as so little exact information is available. At the Ohio 

 experiment station in 1909 the result of the disease was that ''the 

 station plats averaged 69 bushels per acre and the county averaged 

 186 bushels. The preceding 4-year average for the station was 180 

 bushels, while that for the county was 101 -bushels." The county 

 was also infected with wilt, as the same writer shows; but, disregard- 

 ing this and the fact that the station yield should have been nearly 

 double the county yield, and estimating that only 5 per cent of Ohio 

 fields were as badly affected, the loss totals over 870,000 bushels for 

 Ohio alone. 



CONTROL OF FUSARIUM WILT. 



The problem of control has not yet been worked out for Fusarium 

 wilt. The most promising lines of attack are three: (a) A healthy 

 seed supply, (h) rotation of crops, (c) the development of resistant 

 varieties. 



The use of Fusarium-infected seed should be avoided even where 

 the disease is already in the land. It not only increases the severity 

 of the wilt trouble, but gives defective germination. Failures due to 

 decay of the seed potatoes after planting are especially frequent in 

 the West, as, for example, in Colorado in 1908 and in California in 

 1912. These are attributed to Fusarium, but the recent studies of 

 Wollenwebcr show that Fusarium oxysporum does little more than 

 lower the vitality and afford an entrance for other organisms 

 which destroy the seed potatoes after planting. F. trichothecioides 

 in the West and F. coeruleum in the East are the best known of these 

 tuber-decay producers. To what extent other organisms are involved 

 remains to be determined. 



