1 I15ER CROPS 391 



inches deep, turning it over flat. After it has rotted one season 

 it is cross-plowed about four inches deep, thus covering the 

 rotted sod with about two inches of fresh soil. This is known as 

 "back setting." On soil thus prepared wheat is usually sown. 



It has been the custom in the states farther south to plant 

 maize upon the freshly turned sod, producing a crop with little 

 or no cultivation, while in Minnesota, the Dakotas and western 

 Canada it has been the custom to sow flax; thus a crop is se- 

 cured while waiting for the sod to rot. Flax seed is there- 

 fore a sort of by-product in the development of a new country, 

 and this source of supply has been sufficient to meet the market 

 demands. Further, soils soon become "flax sick" on account of 

 the wilt disease, which causes the abandonment of flax culture 

 in older regions. 



495. DISEASES. Flax is attacked by several fungous diseases. Soil on 

 which such attacks have occurred is known as flax sick soil. These diseases 

 are the most serious hindrance to the successful cultivation of flax, either for 

 seed or for fiber, but in no way do they affect the growth of other field 

 crops. The most common one is the flax wilt disease (Fusarium lini Bolley), 

 so called because the plants, attacked at all ages, die as if for want of water. 

 This fungus starts from the infested soil or seed, and develops spores on the 

 surface of the stems, and also within the stems and the seed. The remedy 

 consists in a rotation of crops, in which flax occurs only once in eight years, 

 and the sowing of pure, well-matured, clean seed. The North Dakota Station, 1 

 which discovered this disease, states that all samples of seeds examined con- 

 tain spores. Internal spores of diseased stems and seeds cannot be killed by 

 treatment. Hence all bits of stems and diseased seeds must be removed, after 

 which the pure, undiseased seeds may be treated with formalin, as for seed 

 wheat , and oats. (C. A. 149) The itinerant threshing machine tends to 

 spread the infection. Manure from animals fed on flax straw must not be 

 used where flax is to be grown. 



Another species of the genus Fusarium, a species of Collet otrichum and of 

 Alternaria, are destructive to flax. Flax rust (Melanospora lini (D. C.) Tul.), 

 recognized by the yellow or orange spots on the older parts of the nearly 

 mature stems, is not considered seriously injurious to flax grown for seed. 



496. Cultural Methods. The culture of flax for seed is 

 similar to that of spring wheat. For the best results on old 

 land rather deeper and more thorough preparation of the soil is 



i North Dakota Sta. Bui. No. 50 (1901); No. 55 (1903). 



