4 BULLETIN 1120, U. S. DEPARTMENT OF AGRICULTURE. 



Numerous inoculations with fungi and bacteria from these isolations 

 always failed to produce symptoms identical with those of the type 

 of flax canker under consideration. Hence, this prehminary work 

 indicated more and more clearly that this type of flax-canker injury 

 was due to causes of a nonparasitic nature. 



FIELD OBSERVATIONS. 



A number of observations had tended to indicate that excessive 

 heat at the soil line during the seedling stage possibly was the cause 

 of the trouble. For a number of years it had been noticed at Mandan, 

 N. Dak., that flax cankered more in the nursery plats than in the rota- 

 tion plats. In the former the rows were spaced rather widely, flax 

 was sown rather thinly, and the plats were kept free from weeds. In 

 the rotation plats the rows were closer together, the flax was sown 

 more thickly, and weeds were allowed to grow. As a result of these 

 two sets of conditions, the soil was much more exposed to the intense 

 sunlight in the nursery plats than in the rotation plats. Indications 

 pointed, therefore, to intense sunlight as being the most important 

 factor in causing canker. Furthermore, for a considerable time it had 

 been noted that flax canker had been most severe in flax on breaking 

 (freshly turned sod) , where weeds are practically absent and a thin 

 stand usually occurs. By contrast, flax fields on old land usually are 

 weedy. This canker, therefore, developed both in the nursery and in 

 fields under similar conditions; that is, the most canker occurred 

 where conditions made it possible for the intense sunlight to strike 

 the bases of the young flax plants with the least interference from weeds 

 and other flax plants. Likewise, in a series of experimental plats at 

 Fargo, N. Dak., in 1917, in which the stand varied greatly because of 

 variation in germination of seed, it was noted that the most flax 

 canker resulted where the stand was thinnest. The results of these 

 three sets of observations are summarized in Table 1 . 



Table 1. — Summary of field observations of heat canker of fiax on plats and under field 



conditions in 1917. 



Location and field condition. 



Canker under different conditions . 



Thin stand; no weeds. 



Thick stand; weedy. 



Mandan, N. Dak.: 



Nursery plats 



Canker abundant 





Rotation plats ^ 



Canker slight or absent. 



Farms: 



Breaking (thin stand; few weeds) 



Canker abundant 





Old land (thick stand; many weeds) 



Do. 



Fargo plats: 



Thin stand 



Canker abundant 





Thick stand 



Do. 









These observations show that flax canker occurred most abun- 

 dantly where the bases of the young flax plants and the adjoining 

 soil were exposed to intense sunlight, on account of the thin stand 

 and the absence of weeds. 



