32 COOPERATIVE MARKETING 



A very important problem, but one which has not yet been 

 satisfactorily solved, is the prevention of loss by frost. A 

 citrus grove can stand very little cold, and any temperature 

 lower than 27 or 28 degrees, Fahrenheit, continuing for 

 some time, ruins the fruit. If the thermometer falls to 24 

 degrees or lower for any length of time the trees are more 

 or less seriously damaged. The importance of frost pro- 

 tection was forcefully brought home to the growers during 

 the season of 1912-13 by a frost which destroyed millions 

 of dollars worth of fruit and caused injury to the orchards 

 which it is difficult to estimate. However, this frost was 

 the first ruinous one that occurred in the history of the 

 California citrus industry. 



Many methods of artificially raising the temperature in 

 groves are in vogue. Irrigation water is sometimes run 

 in the furrows in order to take advantage of the latent 

 heat stored in the water. More common are various firing 

 devices. Wet straw is at times burned at different places 

 in the grove so that the smoke may form a cloud and shield 

 frozen fruit from the direct rays of the morning sun, and 

 thus prolong the thawing process, for much more damage 

 is done by rapid thawing than by freezing. Most common 

 is the liberation of artificial heat to keep the fruit from 

 freezing. Baskets of coal or briquets have been used for 

 this ptu'pose, but now the almost universal fuel is petroleum 

 in some form, crude oil or slop distillate. This is fired in 

 some kind of oil heater, of which there are numerous makes. 

 Some groves even have an elaborate oil reservoir system 

 with oil pipes down every row and heaters controlled from 

 a central point. A good heating system can raise the tem- 

 perature six to ten degrees. This is practically always 

 enough to prevent frost injury, but for reasons which will 

 be stated later the present widespread use of devices for 

 frost protection is likely to decline. 



