406 DISEASES OF ECONOMIC PLANTS 



Attacks of the mite cause a similar appearance. 



Shedding {Physiological). — This occurs chiefly following 

 extremes of either dry or wet weather or following a change 

 from one extreme to the other. 



FLAX 



Wilt, fusariose (Fusarium lini Bolley). — A condition 

 of soil known as "flax sick" has prevailed in many sec- 

 tions of the country to such an extent as to cause the 

 abandonment of flax as a crop. This is notably true of 

 Iowa, Minnesota, North and South Dakota. On such 

 soils flax plants are attacked at any age, and die early or 

 late according to the time and intensity of the attack.^ 

 Many of the plants in an aggravated attack are killed 

 before they appear above the surface of the ground. Such 

 field spots become centers of disease ; they enlarge through- 

 out the summer, and new plants sicken, wilt, and die around 

 their margins, finally giving the entire field a spotted ap- 

 pearance. Young plants wilt suddenly and dry up, or 

 decay if the weather is moist. Older woody plants become 

 sickly and weak, turn yellow, wilt at the top, and die 

 slowly. Such plants are easily pulled up, owing to their 

 decayed root system. 



Most of the roots of diseased plants are dead and have 

 a characteristic ashen-gray color. If the plant is attacked 

 late in the season, this gray color may be limited to one side 

 only of the taproot. In such cases the leaves and branches 

 on the affected side are blighted. If the disease is sowed 

 with the seed upon healthy soil, only a few plants may be 

 attacked during the first year, and such plants may be very 



» Bolley, H. L., N.Dak. Agr. Exp. Sta. Bui. 50, December, 1901. 



