POTATO DISEASES 



1713 



Cause 



Numerous inoculation experiments 

 have shown that this dry rot is caused 

 by a parasitic fungus, for which we have 

 proposed the name Fiisarium tuherivo- 

 rum. At the same time it has also been 

 demonstrated that this dry-rot fungus 

 does not cause the injury to the leaver 

 and stems often referred to as "blight" 

 or "wilt." In other words, the present 

 dry rot of the tuber is not connected in 

 any manner with diseased conditions of 

 other parts of the plant. 



Methods of Control 



Experiments at the Nebraska station 

 in 1912 demonstrated that the disease 

 could be held in check by the use of 

 lime-sulphur wash, boiled in the usual 

 manner in proportions of 5 pounds of 

 lime to 5 pounds of sulphur in 15 gal- 

 lons of water, formalin dip and formalin 

 vapor. The dip and vapor treatments 

 follow: 



Formic aldehyde solution. The tubers 

 were placed in sacks and dipped for two 

 hours in a solution of one pint of 40 

 per cent formic aldehyde solution (often 

 called "formalin") in a barrel of water. 

 The tubers were then dried before being 

 placed in storage. 



Formic aldehyde vapor. The tubers 

 were exposed to the vapors generated by 

 23 ounces of potassium permanganate 

 placed in 3 pints of a 40-per cent solu- 

 tion of formic aldehyde (formalin) to 

 each 1,000 cubic feet of space. 



E. M. Wilcox and G. K. K. Link, 



Nebraska Experiment Station Bulletin 134. 



Dry Rot or Wilt 



Fusarium oxysporum 

 F. D. Bailey 



This fungous disease is both a field and 

 a storage trouble of wide distribution and 

 often causes considerable loss. The 

 trouble has long been known both in this 

 country and in Europe, but little was 

 known until recently concerning the exact 

 cause. In the United States the "dry 

 rot" has long been recognized as a seri- 

 ous trouble; just what the actual loss 

 amounts to it would be impossible to de- 

 termine. The damage in the field is even 



harder to estimate, for many times the 

 grower is not aware of any disease or 

 abnormal appearance. 



Distribution 



In the Northwest the disease is ap- 

 parently wide spread. Investigations 

 throughout the Willamette valley and 

 lower Columbia basin during the sea- 

 son of 1911 showed very few fields entire- 

 ly free from the disease. The season of 

 1912 being exceptionally wet, this trouble 

 seems not to have shown up as extensive- 

 ly. 



Symptoms 



The wilt disease makes its attack on all 

 parts of the plant below ground. It gen- 

 erally enters through a root and spreads 

 to all other parts beneath the surface. 



The first indication of the disease is a 

 different appearance of the foliage. It 

 gradually takes on a lighter color, loses 

 its glistening appearance, and the leaves 

 roll in during the heat of the day. (Fig. 

 1.) If the plant is attacked while growth 



Fiff. 1. Wilt of Potato Vine Caused bv the 

 Soil Fungus, Fusarium. Dry stem-end rot 

 of tubers is caused by the same org^anism. 



is still taking place, it is quite certain to 

 be dwarfed. The death of the plant comes 

 on slowly and to the casual observer 

 would seem to be little different from the 

 normal maturing. It is premature, how- 

 ever, and the yield is much cut down. 

 It has been shown that the growth in 



3 — 2.-5 



