FIBER PLANTS 405 



Sore shin, rhizoctoniose {Rhizodonia sp.). — Primarily 

 this is an ulcerous wound upon the stem near the 

 ground, accompanied by reddening or browning of the 

 leaves. If the ulcer enters deep into the stem, so as to 

 interfere with the ascending sap, it may cause death, 

 though this is usually prevented by heihng of the wound 

 before the disease has progressed too far. The disease is 

 often caused by the attack of rhizoctonia, especially in 

 tissues predisposed to such attack by weakness. 



Harrowing, to aid in drying the surface soil, to some ex- 

 tent prevents the attack and development of this fungus. 



A similar disease may also result from purely mechanical 

 injuries caused by tools. 



Mosaic, yellow leaf blight, black rust {Physiological). — 

 The first signs of this disease are yello\vish spots which 

 give the leaf a checkered appearance. The discoloration 

 occurs first in small areas, which are roughly rectangular 

 owing to limitation by the veins, and which are situated 

 at points most remote from the main feeding veins. In 

 later stages these weakened areas may be overgrown by 

 various saprophytic fungi. Usually the centers of these 

 spots soon turn brown, and the brown part enlarges and 

 shows a series of concentric markings. If very dark-colored 

 fungi grow upon these spots, they soon become black-coated 

 and take the popular name " black rust." 



Kainit, used as fertilizer, often reduces the damage from 

 mosaic. 



Red leaf blight (Physiological). — This reddening, re- 

 sembling autumnal coloration, occurs most frequently 

 toward the season's end and is most common upon poor 

 soil. It is due chiefly to lack of nourishment. 



