APPLE POWDERY MILDEW AND ITS CONTROL. 3 



progress in Europe and elsewhere. In 1907, when the work in the 

 Pajaro Valley was started, it was naturally assumed that some of the 

 spray mixtures recommended, either in this country or abroad, would 

 prove successful in controlling the disease in that district. Such was 

 not the case, however, and several seasons have been spent in develop- 

 ing a method that can be used satisfactorily. 1 One source of delay in 

 arriving at a practical solution of the problem has been the peculiar 

 climatic conditions of the Pajaro Valley, which distinguish it from 

 any other large apple district in the United States. It will not be 

 out of place to call attention to some of these peculiarities. 



CLIMATIC CONDITIONS OF THE PAJARO VALLEY. 



The Pajaro Valley lies along the northern shore of Monterey Bay 

 and is situated about 75 miles south of San Francisco Bay. As is 

 common to California in general, the year is divided into two seasons, 

 the rainy and the dry. The rainy season extends from the latter 

 part of October to the month of April, and during that time there 

 is an average precipitation of about 25 inches. Throughout the 

 remainder of the year showers are rare and of practically no im- 

 portance. The winter weather is mild and comparatively little frost 

 occurs. 



In the summer and early fall the valley is subject to winds from 

 the ocean. These winds are of low velocity and produce no apprecia- 

 able wind damage. They commence about noon and continue to 

 blow until evening. As a result the evenings and nights are cool 

 or even chilly. Very frequently the winds bring in fogs, which begin 

 to cover the valley about 4 o'clock in the afternoon and remain until 

 9 or 10 o'clock the following morning. These fogs, of course, ob- 

 scure the sun. They are of two types, high and low. The main 

 body of the high fogs is at an elevation of perhaps a thousand feet, 

 and in consequence the foliage of the trees is not much dampened. 

 On the other hand, the land fogs lie close to the ground and envelop 

 the trees, drenching the foliage so that the leaves often drip profusely 

 during the night and early morning. This foggy weather is not 

 continuous, but is interspersed with clear periods of 2 to 10 clays. 

 During the foggy weather the daily fluctuation of the temperature is 

 between 50° and 65° F., and in the clear periods the range is from 

 65° to 80° F. Temperatures above 90° F. are rarely experienced more 

 than once or twice during the summer. 



1 During the time these investigations have been in progress near Watsonville, Cal., a 

 considerable portion of the orchards of the C. H. Rodgers estate has been given over 

 each year to experimental work, and in the past two years spraying and pruning ex- 

 periments have also been conducted in the orchard of Mr. O. D. Stoesser. In addition, 

 the hearty cooperation of many other growers in the valley has been of material assist- 

 ance in determining from a commercial standpoint the feasibility of the control methods 

 recommended. ' 



