EFFECTS OF FREEZES ON CITRUS IN CALIFORNIA 315 



A TEST OF THE EFFICIENCY OF ORCHARD HEATING 



BY A. D. 8HAMEL, L. B. SCOTT, AND C. S. POMEROY 



United States Department of Agriculture 



The serious damage done by the freeze of 1913 awakened a general 

 interest in ways and means for protecting citrus orchards from this 

 danger. In many sections various means of protection were in use 

 during the freeze, but exact figures were lacking in many cases as to 

 the profitableness of the heating methods used. 



The opportunity of securing some practical information in an 

 experimental way on the results that had been obtained seemed too 

 good to lose. Consequently the writers in co-operation with Dr. H. J. 

 Webber of the Citrus Experiment Station of the University of Cali- 

 fornia decided to secure data on this subject in connection with their 

 citrus performance-record work for the improvement of citrus fruits 

 by bud selection. 



After consultation it was decided to confine observations to lemon 

 varieties and to orchards located in the Corona district. In this 

 district an unusual number of groves were protected by heaters during 

 the freeze, and in many cases unprotected orchards adjoined the pro- 

 tected ones. 



Shortlj* after the freeze, a committee of Corona lemon growers, 

 Dr. H. J. Webber, and the writers visited most of the lemon groves 

 in the Corona district for the purpose of determining whether or not 

 reliable data on the efficiency of the methods of orchard protection 

 could be obtained. After a careful survey of the situation, it was 

 unanimously decided that such information could be secured under 

 fair and comparable conditions. Therefore, several orchards were 

 selected for study and observation that in the opinion of every one 

 in the party were suitable for this purpose. 



The plan of study agreed upon was to keep performance-records 

 of comparable plots of trees in heated and unheated groves, beginning 

 with the first pick after the frost and continuing for at least- one year, 

 and if advisable for a longer period of time. 



It was soon apparent that lemon varieties differ in their resistance 

 to frost. So it became necessary to compare heated and unheated 

 orchards of the same variety. Not only was this difference very 

 evident, but different types in the same variety apparently differ in 

 resistance to frost, so that it became necessary to compare trees of the 

 same type in heated and unheated groves. 



