1 66 SEMITROPICAL FRUITS 



it has wings. It can easily be told from the other pests found 

 on citrus trees, because it is snow-white when full grown. 



When the wings are at rest, the insect is 



about the size of the letter o used in this 



paragraph. 

 The remedy is a severe one, for the pest is 



hard to get rid of. The tree must be stripped 

 FIG 95. white Fly f ^s leaves and thoroughly fumigated before 

 with wings closed. the insect is growDj or no thing can be done to 



save the tree. 



Diseases of Citrus Trees 



Gum Disease. This disease, which usually affects the 

 trunk of the tree near the ground, sometimes comes as a 

 result of letting irrigation water come in contact with the 

 stem of the tree. By keeping this water from touching the 

 tree, one cause of the disease will be removed. 



Other causes, still unknown, however, are likely to produce 

 the disease. From whatever source the trouble comes, the 

 portion of the bark which is diseased must be cut away, also 

 the diseased wood beneath, and the wound covered with 

 something, such as rubber paint, which will keep the sap 

 from running out. Removing the soil from the lower part 

 of the trunk is also helpful. 



Chlorosis. This disease causes the leaves of the tree to 

 turn yellow. In the case of the orange and lemon it is com- 

 monly brought about by the lack in the subsoil (page 30) of 

 some food element that the tree needs, or else by there being 

 too much of some one element. Orange and lemon trees re- 

 quire lime, but many California soils have in them more lime 



