SEMI-TROPICAL FRUITS 199 



fruit which comes up to this standard is satisfactory from the 

 point of sweetness to the average consumer. 



290. Insect pests. Orange and lemon trees are subject 

 to the depredations of many insect enemies, but especially of 

 that group known as the scale insects. Wherever the orange 

 tree grows, scale insects of some sort are almost certain to be 

 found in abundant quantity. The type causing most injury 

 varies in the different localities, depending on climatic con- 

 ditions and other factors. In Florida the chief pests are the 

 white-fly, rust-mites, and scale insects. In California the red, 

 black, brown, and citricola scales, and the mealy bug give 

 most trouble. 



291 . Control of insects. There are two methods of insect 

 control; spraying and fumigation. Spraying is practiced 

 most commonly in Florida, fumigation in California. The 

 former is cheaper but needs to be repeated much oftener, and 

 constant care has to be exercised not to injure the evergreen 

 foliage of the tree. 



The fumigation method, also, must be performed with 

 great care. If the temperature is too low or too high, or if 

 the atmosphere contains too much water-vapor, the foliage 

 and fruit may be seriously injured. For this reason, the work 

 is always done at night, and care is exercised at each step of 

 the process to avoid possible injury to the tree. 



292. Citrus canker. In recent years there appeared in 

 Florida a citrus disease of such serious nature that the aid of 

 the United States Government was invoked to bring about 

 its control. This was the so-called citrus canker. It is an 

 exceedingly virulent disease, attacking not only leaves and 

 twigs, but fruit and stems as well. In its efforts to control 

 citrus canker, the United States Department of Agriculture 

 maintained a rigid quarantine wherever the disease was 

 known to exist, in order to prevent its spread to new locali- 

 ties; and all diseased trees were burned as soon as they were 

 discovered. A large appropriation for carrying out these 



