DISEASES 33 



Mosaic disease is characterised by yellow spots, 

 which arise on the leaves and occur in a more or less 

 regular order, thus producing a kind of mosaic pattern. 

 As the disease extends, the leaves frequently curl up 

 and fall to the ground. This affection is very often 

 aggravated by the attack of certain fungoid organisms. 

 The most effective remedy is thorough cultivation 

 with a view to improving the physical conditions of 

 the soil. It has been found that the application of 

 kainit to the soil is very beneficial probably owing to 

 its power of binding the particles of soil more closely 

 together and thus enabling it to retain moisture. 

 The same effect can be produced by rolling the land. 



The occurrence of red leaf blight is manifested by 

 the leaves turning red. The growth of the plant 

 gradually ceases and the leaves fall. This disease is 

 due to the poverty of the soil, and indicates a lack of 

 potash, nitrogen, and probably also of phosphoric acid. 

 The obvious remedy is to supply the necessary food 

 constituents by suitable manuring. 



The shedding of bolls not uncommonly causes 

 considerable damage in cotton plantations, and is 

 evidently provoked by unfavourable climatic condi- 

 tions, since it occurs most frequently in times of 

 drought or excessive rainfall. 



Angular leaf spot is so called on account of dark 

 angular spots which appear on the leaves. These 

 spots at first present a watery appearance, but later 

 become black and then brown. It is always the less 

 vigorous plants which are attacked by this disease, 

 and it is therefore evident that the method of pre- 

 vention is to sow good, sound seed and to cultivate 

 carefully so as to give the plant the means of develop- 

 ing satisfactorily. 



Fungoid Diseases. The principal diseases of this 

 nature are anthracnose, wilt or frenching, root rot, 

 cotton leaf blight, mildew, and cotton boll rot. 



Anthracnose is due to the fungus known as Colleto- 

 trichum gossypii. The malady may make its appear- 

 ance on the bolls, stems, or leaves. When it occurs 

 on the bolls, it first becomes visible as small, dull 

 reddish spots, depressed in the centre. As the spots 



