DISEASES OF COTTON 235 



(3) Rotating 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. 



(5) Poisoning by use of calcium arsenate, applied with a dust- 

 gun, when the air is calm and the plants are moist, usually at night. 

 (Details of this method can be secured from the United States 

 Department of Agriculture). 



The Pink Boll-worm (Pectinophora gossypiella). This dan- 

 gerous insect is a native of India, but apparently does little damage 

 to native cotton. It was apparently introduced into Egypt about 

 1906 and into Brazil and Mexico about 1911. An infection was 

 discovered in Texas in 1917, but so far has been kept under control. 

 The pink boll-worm is very destructive in Mexico and is considered 

 a very dangerous insect. 



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

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

 structive. 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 (anthracnose) , 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 



