328 CITRUS FRUITS AND THEIR CULTURE. 



the trees during the dry season to check the ravages of red 

 spider. This insect cannot withstand the presence of a 

 considerable amount of moisture on the trees. 



It must be conceded, however, that the cheapest way 

 to distribute water in a grove of orange trees is to allow 

 it to run in furrows over the surface of the ground and, 

 other conditions being equal, this method should be given 

 preference. Less power is required to provide the supply 

 and the equipment is, on the whole, less expensive. On 

 clay soils or soils with a clay subsoil close to the surface, 

 and with sufficient fall, it is the best plan to follow. 



IRRIGATION IN CALIFORNIA AND ARIZONA. 



In California and Arizona, it is not possible to main- 

 tain a grove of citrus trees without resorting to irriga- 

 tion. The water supplied by rainfall is insufficient for 

 their needs, and a considerable amount of the cost of 

 fruit production must be charged to the irrigation ac- 

 count. Prof. Newell says, "The annual charge for the 

 irrigation of citrus lands in southern California varies 

 from $5 to $30 per acre, and will probably not average 

 far from $10 per acre irrigated, the supply being usually 

 12 inches in depth of irrigation water." 



The amount required in different localities and even 

 on adjacent ranches varies greatly. The following table 

 copied from Bulletin No. 108, U. S. Department of Agri- 

 culture, Office of Experiment Stations, by Prof. E. J. 

 Wickson, shows the season of year during which irriga- 

 tion is practiced, the amount of rainfall and the amount 

 of irrigation water supplied in several of the citrus dis- 

 tricts : 



