CALIFORNIA AVOCADO ASSOCIATION 



49 



COLD RESISTANCE OF THE AVOCADO 



By H. J. Webber, Director, Citrus Experiment Station, Riv- 

 erside, California 



Several rather cold periods of weather having occurred during the 

 winter of 1916-17, it was thought desirable to collect information regard- 

 ing the effect of the cold on the different varieties of avocados. It is highly 

 important in this early stage of the industry to have as reliable information 

 on this matter as it is possible to obtain. Early in the winter, the writer 

 sent a letter to each member of the Avocado Association, requesting him to 

 make observations as to comparative injury on his different trees and report 

 these observations. Carefully prepared statements were received from 

 some fifty different members, and the writer desires to extend his thanks to 

 these members for their kind co-operation. 



The conditions were so variable in different places, and the tempera- 

 ture records reported so unreliable in many instances, that it has not ap- 

 peared to the writer to be profitable to report the different observations in 

 detail. Certain points were reported, however, in sufficient harmony to 

 indicate their reliability, and these observations may thus be taken as fairly 

 conclusive evidence. A summary of the conclusions from a study of the 

 various reports follows: 



Factors Influencing Injury 

 Age of Tree. — Of the same variety, young trees are much more easily 

 injured than old trees. In several instances nursery trees of a variety were 

 killed to the ground, while five to eight-year-old budded trees sustained no 

 appreciable injury, only the young, growing tips being injured. In analyz- 

 ing the reasons for this result, it must be remembered that the cold is usually 

 most severe near the surface of the ground. The tender shoots and branches 

 on an old tree are much further from the ground than on the young tree, 

 and in a warmer zone. Wood of the same age on an old tree may be just 

 as tender as that on a young tree. 



Condition of Growth. — The observation was very generally made 

 that trees in a condition of rapid growth were much more injured than 

 similar trees of the same variety that had completed their growth and were 

 more or less dormant. In the same orchard, trees side by side frequently 

 showed marked differences. One tree, in rapid growth, exhibited injured 

 young leaves all over its surface, while a tree of the same variety, next to 

 it, having no young growth, showed no indication of injury. This is 

 apparently not merely a difference of age of wood or branch injured, as 

 the older leaves on a rapidly growing tree showed more injury than similar 

 leaves on the dormant tree. 



Constitutional Condition. — Vigorous, healthy trees showed 

 much less injury than trees weakened by disease, transplanting, or other 

 causes. Trees, newly planted, that had not fully recovered from the shock, 

 were severely injured. Weak, sickly looking trees, which occur to some 

 extent in almost every planting, suffered much more than good, vigorous 

 trees of the same variety and age. Trees with weak tops from poor bud 

 unions showed severe injury. Apparently any condition that results in 

 weakening the trees, — such as, poor cultivation, poor irrigation, disease, 

 or mechanical injury, — renders the tree more susceptible to cold injury. 



