EFFECTS OF FREEZES ON CITRUS IN CALIFORNIA 267 



drier than the other trees of the grove, as is made evident by the 

 lighter crops on these rows, and this puts these trees in a different 

 condition to resist cold. It has been found that trees that were dry, 

 provided they were not actually suffering and weakened because of 

 drought, were less easily damaged by the cold than trees which had 

 a more plentiful supply of sap or were in more active growth. 



A few groves were found where the rows next to the windbreak 

 had been kept in practically as good condition as the other trees of 

 the grove by giving them extra water and fertilizer. In some of these 

 groves it was also possible this year to notice a slightly better condition 

 of the rows next to the windbreak. 



It seems certain from all of the evidence collected that windbreaks 

 did exercise a distinctly modifying effect in this freeze on the damage 

 caused to the trees for a short distance to the leeward of them; but 

 this advantage was slight, and, in view of the rareness of the occur- 

 rence of such severe freezes accompanied by wind, it would not, as a 

 whole, seem wise to advocate the use of windbreaks for frost pro- 

 tection only. They take up much valuable space and when the tem- 

 perature is that of a "frost" rather than a freeze the protection that 

 the windbreak gives to the leeward side is likely to be offset by the 

 increase in damage on the windward side. 



Effect of Running Water or Irrigation During Freeze. One of the 

 first methods of protection to suggest itself to growers was to run 

 water through the grove. The water would have to give up much 

 heat in being cooled, and if water freezes a large amount of heat is 

 released. 



When conditions were such that all the factors were the same 

 except for the presence of running water, the groves that were under 

 water sometimes looked better than those which were not. 



In one grove only 5 per cent of the fruit (navels) from that portion 

 of the orchard which was irrigated during the cold was rejected at 

 time of shipping, whereas 100 per cent of the fruit from the non- 

 irrigated portion was frozen. Other conditions were apparently sim- 

 ilar. The fruit was picked some time previous to March 28. 



In three citrus nurseries well defined benefit from running water 

 during the freeze was apparent, and one small orchard of 500 one- 

 year-old Valencia trees was found where one-half of the trees had 

 been irrigated during the entire cold spell from Sunday afternoon 

 until Wednesday morning. Ten per cent of the non-irrigated trees 

 were killed and the outer layer of growth on the remaining 90 per 

 cent was badly injured, while the irrigated trees showed practically 

 no frost injury. 



