562 Protection of Orchards from Spring Frosts, [oct., 



Mr. P. J. O'Gara, who was in charge of these investigations, 

 is that frost injury to fruit trees may be prevented by the 

 use of fires and smudges. He found that the difference 

 between smudged and unsmudged areas was very marked; 

 in several instances the treated orchards set a full crop, while 

 in those similarly situated but untreated the crop was entirely 

 destroyed. Cases are, quoted showing the results obtained by 

 various growers at a relatively small cost. 



It may^be of interest to give the approximate temperatures 

 at which, according to Mr. O'Gara's observations on the 

 Pacific Coast, the principal orchard fruits are liable to be 

 injured by frost. These temperatures would, however, vary 

 somewhat according to the weather conditions preceding the 

 frost, and they may also be only of local application. 



Temperatures Injurious to Fruit when in Bud, in 





Blossom 



, &C. 





At 





In 



In 





other 





bud. 



blossom. 



Setting fruit. 



times. 





0 F. 



0 F. 



0 F 



0 F. 



Almonds 



... 28 



3o 



30 



28 



Apples 



. ... 27 



29 



30 



25 



Apricots 



... 30 



31 



31- 



30 



Cherries 



... 29 



30 



30. 



29 



Peaches 



... 29 



30 



30 



28 



Pears ... 



... 28 



29 



29 



28 



Plums ... 



... 30 



3i 



31 



29 



Prunes... 



... 30 



3i 



31 



29 



In considering the utility of the foregoing methods, it is 

 obvious that the main difficulty is to know when an injurious 

 frost is likely to occur. A careful study of local weather 

 conditions is necessary, supplemented by a psychrometer for 

 determining dew-point temperatures, thermometers indicating 

 the temperature in the orchard, and a barometer to indicate 

 the pressure of the atmosphere. The Weather Bureau of 

 the United States issues warnings and forecasts as to the 

 occurrence of frosts and cold-waves, and in the experiments 

 in Oregon these were found to be of great value. They 

 were forwarded by telegraph and telephone to the officer in 

 charge, and as far as possible to the individual growers. 



A careful study of the psychrometer, or wet and dry bulb 

 thermometer, is essential, as from this, by the aid of suitable 

 tables, the dew-point can be ascertained, and under certain 

 conditions the determination of the dew-point will give 



