FUNGOID DISEASES 35 



The only remedy for wilt is the production of a 

 variety capable of resisting the disease. Such re- 

 sistant forms have been developed by selection in the 

 United States, and it is considered that by this means 

 the Sea Island cotton industry has been saved from 

 extinction. 



Root rot is produced by a fungus (Ozonium sp.) 

 which attacks not only cotton, but many other plants, 

 including apple trees, the paper-mulberry, and lucerne. 

 The fungus attacks the root and feeds on the material 

 contained in its tissues. The roots gradually wither 

 and decay and are therefore unable to absorb material 

 from the soil and supply the plant with the necessary 

 food and water. The roots of a plant which has 

 succumbed to this disease bear numerous small white 

 excrescences on the surface. The only method of 

 keeping the fungus under control is by means of a 

 system of rotation of crops. Cereal crops are suitable 

 to grow in such a rotation as they are not attacked 

 by the pest. Cotton should not be planted more than 

 once in three or four years in areas which have been 

 infested with root rot. 



Cotton leaf blight is a common malady of the cotton 

 plant, but does not often cause much injury. The 

 fungus (Sphcerella gossypind) usually attacks the older 

 leaves of the plants as well as those which have 

 received some injury affecting their powers of nutri- 

 tion and assimilation . The disease is not uncommonly 

 found affecting the leaves of plants which have been 

 attacked by other diseases, such as mosaic disease. 

 Leaf blight is characterised by small spots which are 

 white or pale brown at the centre and reddish at the 

 edge. The prevention of this disease may be secured 

 by adopting methods of cultivation calculated to 

 render the environment more suitable for the cotton 

 plant. 



Cotton mildew arises on the surface of the leaves in 

 small areas bounded by the veinlets. This fungus 

 (Ramularia areola) seems to cause but little damage 

 to the crop, although it is sometimes produced fairly 

 abundantly. 



Cotton boll rot, black arm, and bacterial disease are 



