2 BULLETIN 959, U. S. DEPAKTMENT OF AGRICULTTJEB. 



THE GRAND VALLEY OF COLORADO. 



The Grand Valley is one of the most important fruit-growing 

 regions of Colorado, having approximately 15,000 acres devoted to 

 such fruits as apples, pears, peaches, plums, cherries, and bush fruits. 

 About 10,000 of these acres are planted to apples and 2,500 to pears, 

 both of which (and particularly the apple) are heavily attacked by 

 the codling moth. 



LOCATION AND TOPOGRAPHY. 



The Grand Valley is in the western part of Mesa County and ex- 

 tends from Palisades to Fruita, about 32 miles. The valley follows 

 the course of the Grand River and is generally level, except for the 

 sections known as the Fruit Ridges, which are somewhat elevated 

 and rolling. The district of Orchard Mesa, although higher than the 

 rest of the valley, is typical level, or mesa, land. The lower part of 

 the valley is approximately 4,500 feet above sea level and the upper 

 district at Palisades is about 4,800 feet in elevation. 



CLIMATE. 



The climate is comparatively dry, and the crops are irrigated 

 principally by means of water taken from the Grand River. The 

 annual precipitation is but 8 to 9 inches, and during the five months 

 from May to September, in which season the apple and codling moth 

 are developing, the rainfall amounts to only from 3 to 4 inches. The 

 mean normal temperature during the same period is about 70.6° F. 



COMPARISON . OF THE CLIMATIC CONDITIONS OF GRAND JUNCTION, COLO., AND 



ROCHESTER, N. Y.3 



Since the development and severity of the codling moth are largely 

 influenced by climatic factors, it may be of interest to compare the 

 weather conditions of the Grand Valley with those of the western 

 New York apple belt. Under the semiarid conditions that exist in 

 the Grand Valley, the codling moth causes great injury to the fruit 

 crop and is very difficult to control, whereas under the relatively 

 cooler and more humid conditions of western New York the codling 

 moth is much less troublesome. 



In Table 1 will be found data giving a comparison of the mean 

 normal temperature and precipitation of Grand Junction, Colo., and 

 Rochester, N. Y.* It will be noted therein that the total normal 

 precipitation in the Grand Valley during the growing season, or from 

 May to September, inclusive, is only about one-fourth as much as in 

 western New York and that the mean temperature is about 6° F. 

 higher than that of Rochester, N. Y. 



3 Grand Jiinction, Colo., is the approximate center of the Grand Valley, and Rochester, N . Y., is in the 

 midst of the western New York apple belt. 

 < Climatological data, U. S. Weather Bureau. 



