COTTON 115 



Black Boll. This disease has been reported from 

 Montserrat and Antigua, but the cause is not definitely 

 known. The inner part of the boll decays near the 

 base, the seeds swell up and the lint is destroyed. 

 The bolls drop without opening. 



Texas Root Rot. This disease is not known except 

 in the south-western part of the United States, but 

 may be carried to other places at any time. It starts 

 by causing a few of the plants to wilt and die very 

 suddenly, usually near blossoming, but occasionally 

 when small. The disease spreads to neighbouring plants, 

 and is most severe in hot, wet weather. The disease is 

 due to a iunoms known as Ozonium omnivorum, Shear, 



O 



which attacks the roots and which is always found on the 

 top roots of the diseased plants. The roots are shrunken 

 and have depressed spots with reddish borders. The 

 fungus is white, becoming brown or yellow and finally 

 producing sclerotia. The lint of the diseased plants is also 

 modified, being larger and with fewer spirals than the lint 

 from normal plants. The fungus persists in the soil 

 which precludes direct treatment. It can be controlled 

 by rotating the crops and by selecting seeds from 

 immune plants. 



Root Knots. These peculiar growths are due to the 

 attacks of the nematodes (page 71). When few and 

 scattered they do not cause much damage, but when 

 abundant they reduce the vitality of the plants and 

 frequently cause death. Fortunately the cotton is not 

 so seriously affected as many other crops. However, 

 they cause injuries which are points for infection by 

 many fungi, especially Neocosmospora vasinfecta, and 

 thereby are the indirect cause of very great losses. 



Unfortunately many of our soil-improving plants, 

 such as cow-peas, are also subject to the attacks of these 

 pests, and so cannot be used as rotation crops where the 

 soil has become infected. The grasses and small grain 

 are known not to harbour this pest and, therefore, can 

 be used as rotation crops. However, both the cotton 

 and the grasses and small grain are hard on the land 



