94 



1917 ANNUAL REPORT 



SYMPOSIUM ON HEAT INJURY 



Discussion led by F. O. Popenoe, of Altadena, and Dr. C. L. Ben- 

 nett, of San Dimas. 



F. O. Popenoe : (paper read by Dr. Bennett). It is not surprising 

 that a catastrophe which cost the Southern CaHfornia ranchers a loss of 

 $25,000,000 should so move us as to make us look it squarely in the face; 

 but lightning never strikes twice in the same place, so probably it is not wise 

 to give great consideration to an exceptional event. 



Costly though it proved to be, the hot spell of last June was never- 

 theless an unusual occurrence. So in considering it, let us not only get the 

 value out of the experiences connected with the event itself, but in addition 

 so extend the scope of our consideration and inquiry as to cover the subject 

 of heat injury in a broad and comprehensive way. In order that we may 

 thus realize the greatest value from this discussion, I will ask those taking 

 part in it, to view it in this light. 



The questions before us then, are: Is excessive heat as injurious to 

 the avocado as excessive cold? 



What varieties of the avocado best withstood the excessive heat of 

 last June? 



What is it possible for the orchardist to do to prevent injury by heat? 



What subsequent treatment for his damaged trees will bring them 

 most promptly into good condition again? 



What effect does excessive heat have on the fruit crop? 



The answers in detail will be given by those who take part in the dis- 

 cussion. 



Speaking in general terms, I believe the avocado suffers more from 

 excessive heat than from excessive cold. Fortunately in California we do 

 not often have a season of excessive heat. But there are those times of 

 high summer temperature to be dealt with regularly, which have caused 

 the loss of many a good tree through lack of provision for its safety. I urge 

 our planters to provide the best possible growing conditions for their young 

 trees. Based upon our present knowledge, these conditions seem to be, in 

 addition to those ordinarily required, a suitable shade for the first year, and 

 an ample supply of water for quick application at the beginning of any hot 

 spell. A mulch of straw around the young tree is a great safeguard against 

 reflected heat, which does injury to the bark of the trunk and lower limbs. 



I believe 75 per cent of heat damage is caused by lack of adequate 

 and prompt irrigation on the approach of hot spells. TTiat young avocado 

 trees require more water than citrus trees is an established fact, and we 

 must provide accordingly. Wise is he who never allows his ground to dry 

 out. Keep your irrigation work well caught up, so that the hot spell will 

 not find your ground dry; because it is probable that before you can suf- 

 ficiently irrigate your orchard the damage will be done and some of your 

 weak trees or less resistant varieties will be burned up. The danger is 

 greatest on our foothill slopes, where the soil is often of a coarse, loose, 

 porous character. Such soil heats quickly unless moist, and root damage 

 will also occur. 



Of course the strong growing, resistant tree is as desirable for its im- 

 munity from heat damage as it is for its immunity from injury by other 



