412 



SOUTHERN FIELD CROPS 



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

 continue to live 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-hearing ducts in the roots and stems. The 

 wilting of the leaves is due to the cutting 

 off of their water supplj' by the plugging 

 up of these ducts with the threads of the 

 fungus. 



Cotton wilt may readily be detected l)}^ 

 cutting through the main root or stem ; 

 the layer just under the liark is l)lackene(.l, 

 and throughout the stem the cut ends 

 of the sto]iped-up water-carrying ducts 

 appear as small dark dots (Fig. 181). 



381. Spread and persistence of wilt. — 

 Cotton wilt occurs chiefly in the sandy 

 AND Healthy soils of the 'Southern half of the cotton- 

 CoTTON Stalks. |,p]^ ^his disease f^rst appears in small 



r^:t"1:^in «P«*« i^ *^ fi^l'l- It - extremely im- 

 Rtfm attacked by portant for the farmer to recognize cotton 

 ^' *■ wilt when it first ap]:)cars and while it 



is confined to these small spots, for these diseased areas 

 enlarge rapidly every year when cotton is jilanted 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 Wve in the soil for four or more 

 years, even when no cotton is grown. 



Fig, 181. — Section 

 THROUGH Wilted 



