DISEASES OF THE CITRUS FRUIT 309 



The leaf gumming is very common, especially on the 

 orange. It is more prevalent when the weather is very 

 warm. The gum appears as little drops, usually on the 

 undersides of the leaves. It is reddish brown in color. This 

 trouble is not very serious and should cause no uneasiness. 



The brown rot gumming is caused by the brown-rot fungus. 

 It is most common on lemon trees. The greatest exudation 

 of the gum usually occurs on the trunk of the tree close 

 to the bud union. This disease can be largely prevented 

 by avoiding soil conditions which are the most favorable 

 for the growth of the fungus. Do not allow water to stand 

 around the tree or to come in contact with the trunk. 



Twig gumming is sometimes found on nursery stock. It 

 is thought to be caused when the trees are copiously watered 

 after they have dried out considerably. The gum is found 

 on the twigs and causes the bark to split. The leaves usually 

 drop and the twigs die. 



Rots. Besides the gum diseases there are several rots 

 which are injurious. The foot rot and the toadstool rot are 

 the most important. In Florida the foot rot is well dis- 

 tributed, but it is comparatively rare in the citrus belt of 

 California. The root rot is the result of a fungus which 

 causes the roots to rot. The affected roots soon become 

 soft and slimy and the disease gradually spreads downward. 

 The sour orange is the least susceptible to the attack of the 

 fungus, and the disease is largely controlled by grafting on 

 the sour orange stock. 



Toadstool Rot. The toadstool rot is the result of a fungus 

 growth. This fungus is native to the root of the oaks, but 

 it has been able to flourish on the citrus trees, and it is caus- 

 ing much damage. The disease usually kills the tree in 

 three or four years, the affected tree dying gradually. 

 During a long, rainy season this fungus produces several 

 clusters of brownish colored toadstools from the roots. 

 It is from these toadstools produced as the fruiting bodies 

 that the fungus take the name. At present there is no satis- 

 factory remedy for this disease. 



Brown Rot. The brown rot of the fruit causes great losses 

 annually. The spores of this disease enter the fruit through 



