18 Robert S. Kirby 



where the affected plants were stunted not to exceed one-half the height 

 of take-all-free plants, the reduction in yield was 20.9 per cent; and for 

 the 27.06 per cent of all plants in class 4, where the affected plants were 

 less than one-half as high as normal plants, the reduction was 26.90 per 

 cent. Thus this disease caused an average reduction in yield in the ten 

 varieties of winter wheat tested, of approximately 71.2 per cent. Since 

 plants were not observed to die before the culms started to shoot up, the 

 higher yield of plants recorded as disease-free seemingly was not due to 

 the presence of fewer plants in a given area. In fact, there was evidence 

 to show that the disease-free plants growing in the inoculated rows 

 yielded less per plant than did the plants growing in check rows, where 

 all the plants were free of disease. Thus it seems that the recorded loss 

 due to this disease is probably too low rather than too high. 



The 1922 survey in New York showed that 60 per cent of the infected 

 plants in all fields examined were in class 2, 35 per cent in class 3, and 5 

 per cent in class 4. In applying the same rates of reduction in yield, the 

 average loss in the infected plants would be 66.8 per cent. Since 1.1 per 

 cent of the plants in infested fields were diseased, the loss in these fields 

 was approximately 0.71 per cent. 



SYMPTOMATOLOGY 



The take-all disease affects the roots, the culms, the loaves, and the 

 heads of its hosts, producing definite and characteristic symptoms. 

 Signs 4 of the disease appear on the roots and on the lowest two or throe 

 internodes of the culms. 



Symptoms 



On roots. — Brown necrotic lesions appearing on the roots are the first 

 symptoms of this disease. Such lesions were noticeable on the roots of 

 winter wheat collected from a field on March 21, 1923, and the causal 

 fungus was isolated from several of them. These lesions may completely 

 or only partly surround the root. With the advent of warm spring weather 

 the lesions increase in number, so that by the time the plant enters the 

 jointing stage and sends up tillers (usually May 10 to 20 at Ithaca, New 

 York) the greater number of the roots of badly infected plants are brown 

 and dead and nearly all of the living roots have one or more lesions. 



The killing of the roots progresses from the older to the new r er ones, 

 and to offset this loss the older roots continue to send out an abnormal 

 number of branches which give them a woolly appearance (Plate II, A). 

 New roots are often sent out from a point on the crown immediately 

 above that of the emergence of the old ones. The killing of the roots 

 weakens them to such an extent that a slight pull will break the plant off 

 at or near the crown (Plate 1, B). Because of the fasciculation of the 



« Glossary. /" Laboratory outlines in plant pathology, by H. H. Whetzel, L. R. Hesler, C. T. Gregory, 

 and W. H. Rankin. 1916. 



