40 BULLETIN 64, V. S. DEPAKTMENT OF AGRICULTURE. 



This is a problem in varietal decline that should receive earnest con- 

 sideration. The prevalence of such weak plants should be ascer- 

 tained in any stock intended for propagation, and measures undertaken 

 to provide disease-free seed potatoes in sufficient quantity to meet 

 all demands. 



There are all grades of the condition above described, from pro- 

 nounced types of curly-dwarf to those approaching non.ial vigor. It 

 will fm'thermore be apparent that this is a difference inherent in the 

 varieties or strains under observation. Schander has described a 

 related condition as the ^'Barbarossa disease," so named because 

 it is characteristic of the German variety Barbarossa, In every 

 potato field are found some weaklings, or plants which are merely 

 small, without any curled leaves or dwarfed stems, and without the 

 fungous lesions described under " Rosette." The extent to which these 

 small plants represent a permanent deterioration in the vigor of the 

 stock, and thus a condition related to the curly-dwarf, is a problem 

 not yet settled. Certainly such weaklings should be eliminated when 

 improved seed is desired. 



CONTROL OF CURLY-DWARF. 



Since potatoes from diseased hills can not be restored to vigor, aU 

 such should be rejected for planting. The occurrence of any consider- 

 able number in a field may be taken as evidence of a general decline, 

 requiring that the entire stock be given up and new seed substituted. 



It has already been demonstrated by Prof. Stuart that we have in 

 the method of tuber selection outlined by Webber (1908) a means 

 by which all diseased potatoes may be eliminated from a stock, 

 since when all tubers are cut into four pieces and these planted in 

 adjacent hills all those which show inherited weakness may be 

 eliminated and only the strongest and most productive selected. 



ROSETTE. 



Phases of leaf-roll and curly-dwarf marked by dwarfed growth 

 and the formation of aerial tubers have been described. These symp- 

 toms may, however, result from another cause — the stem lesions 

 due to Rhizoctonia, and no attempt to differentiate potato troubles 

 can be successful which does not take into consideration the varied 

 effects of this fungus. It must be recognized that Rhizoctonia appears 

 to be a more active parasite in America than in Europe and to play a 

 greater r61e in the Western States than in the Eastern. 



Since this article is written primarily to effect a diagnosis of 

 potato troubles, it will not be necessary to review the facts already 

 well known to pathologists relative to the occurrence of Rhizoctonia 

 on its various hosts or to discuss the relationship and parasitism of 

 the several known strains. This subject is being fully reinvestigated 



