412 



SOUTHERN FIELD CROPS 



appearance, and may drop their leaves and die, or they may 

 continue to Hve in an unthrifty condition. 



Cotton wilt is caused by a fungus growth, which enters 

 the plant from the soil through the roots. This fungus, 

 or parasitic plant, consists largely of threads, which stop 

 up the water-bearing ducts in the roots and stems. The 

 wilting of the leaves is due to the cutting 

 off of their water supply by the plugging 

 up of these ducts with the threads of the 

 fungus. 



Cotton wilt may readily be detected by 

 cutting through the main root or stem; 

 the layer just under the bark is blackened, 

 and throughout the stem the cut ends 

 of the stopped-up water-carrying ducts 

 appear as small dark dots (Fig. 181). 



381. Spread and persistence of wilt. — 

 Cotton wilt occurs chiefly in the sandy 

 soils of the southern half of the cotton- 

 belt. This disease first appears in small 

 spots in the field. It is extremely im- 

 stem attacked by portant for the farmer to recognize cotton 

 ^''*- wilt when it first appears and while it 



is confined to these small spots, for these diseased areas 

 enlarge rapidly every year when cotton is planted on the 

 field. In time the entire field becomes infected, and the 

 majority of cotton plants of the ordinary varieties die. 

 Thus the field soon becomes useless for the cultivation of 

 the common varieties of cotton. 



The germs of the disease live in the soil for four or more 

 years, even when no cotton is grown. 



Fig. 181. — Section 

 THROUGH Wilted 

 AND Healthy 

 Cotton Stalks. 

 On right, healthy 



plant ; on left, a 



