DISEASES OF COTTON 235 



(3) Eotating crops, by which means the insect is deprived of its 

 food, since it eats no other widely grown plant but cotton. 



(4) Fumigating the seed in order to prevent the introduction of 

 the pest at planting. 



The Boll-worm (Heliothis obsoleta). The boll-worm is more 

 widely distributed than the boll-weevil, although it is less destructive. 

 It is a small, blue-green worm, with spots and black stripes on its 

 back. It is hatched from the eggs of a moth. Like the boll-weevil, 

 the boll-worm attacks chiefly the squares and tender young bolls. 



Preventive Measures. A trap-crop is the most widely used means 

 of checking the attacks of the boll-worm upon cotton. Such a crop 

 is one upon which the moths prefer to deposit their eggs. Their 

 favorite depository is the fresh silks of corn, and hence corn, planted 

 in strips at intervals among the rows of cotton, is the crop generally 

 used as a trap. The corn should be planted late in order that it 

 may be in silk at about the time the cotton plant sets its fruit. 



The worms may be killed when young by spraying or dusting the 

 plants with arsenical poisons. This is an effective killing method, 

 but its use on an extensive scale is not practicable. 



Diseases of Cotton. The most serious diseases of cotton are 

 boll-rot (anthracncse) , cotton wilt, or black rot, and cotton rust, 

 or black rust. Others are root-rot, root-knot, angular leaf-spot, leaf- 

 blight, sore shin, and mildew. 



Boll-rot. This disease appears as grayish or pinkish spots on the 

 immature bolls. Eventually the entire contents of the bolls may be 

 rotted out. 



Boll-rot is most virulent during wet seasons and at such times it 

 may seriously damage the crop. It makes little progress in dry 

 weather, and therefore an unfavorable condition for its development 

 is created by spacing the plants widely, so that the maximum amount 

 of sunshine will be admitted to the bolls. Certain varieties of cotton 

 are partially resistant to boll-rot and such may be used to advantage 

 in sections where the disease is widely prevalent. The selection of 

 the seed of un infected plants is also recommended as a means of 

 checking the spread of this disease. 



Cotton Wilt. Cotton wilt comes from the soil. It is a thread- 



