Mar. 17, 1919 Fusarium-Blight of Potatoes under Irrigation 301 



health. Lengthened rotation periods employing other crops followed by 

 alfalfa improve the nutritive and mechanical properties of the soil, while 

 a judicious irrigation practice adapted to the particular field and season 

 involved combined with suitable cultivation should constantly main- 

 tain a steady and adequate, but never excessive, supply of moisture and 

 insure suitable aeration. This is the method available to the farmer, so 

 far as he knows what constitutes the best conditions for his land through- 

 out a given season. Third, by the use of whole seed, free from wound 

 or injury, thus preventing seed-piece infection, or at least maintaining 

 the plant free from infection for the maximum length of time. The com- 

 bination of the two last-named measures probably constitutes the most 

 effective measures for control of Fusarium-blight. 



It is believed that more than one species of Fusarium is able to bring 

 about each phase of the bhght. F. oxysporum in pure culture under 

 suitably controlled and natural conditions has been found to do this. 



Three general stages of the Fusarium-blight are recognized. First, 

 the stage in which decay and death of the seed piece and new plant 

 occurs before the new shoot emerges from the ground. Germination 

 may or may not have occurred. Second, the later stage, in which the 

 young plant shows many and diverse symptoms of infection by Fusa- 

 rium spp., often resulting in death. Some of these manifestations are 

 not fatal, and recovery is possible. Third, the mature stage, resulting 

 in death, usually at an advanced state of growth, often with infection 

 and decay of the new tubers. 



Different varieties of potatoes show marked variation in their behavior 

 under the same general conditions. There is an inherent weakness in 

 different strains of the Rural variety toward Fusarium-blight, accen- 

 tuated by the conditions under w^hich the seed was grown. The Pearl 

 variety shows these weaknesses, but to a minor degree, unless brought 

 to a poor condition by previous subjection to disease. 



Vascular infection of the seed is not the starting point of disease, but 

 is one of the conditions assisting in bringing about decreased resistance 

 to new infection from the soil. 



LITERATURE CITED 

 (i) Appel, Otto, and Woi.i,Enweber, H. W. 



I910. GRUNDLAGEN EINER MONOGRAPHIE DER GATTUNG FUSARIUM (LiNK). 



^ In Arb. K. Biol. Anst. Land u. Forstw., Bd. 8, Heft i, 207 p., 10 fig., 



3 pL Verzeichnis der wichtigsten benutzen Schriften, p. 196-198. 



(2) Carpenter, C. W. 



1915. some potato tuber-rots caused by species of fusarium. in jouf. 

 Agr. Research, v. 5, no. 5, p. 183-210, pL A-B, 14-19- Literature, 

 cited, p. 208-209. 



(3) Cromwell, R. O. 



i917. fusarium-blight, or wilt disease, op the soybean. in jout. agf. 

 Research, v. 8, no. 11, p. 421-440, i fig., pL 95. Literature cited, p. 



438-439- 



