April, 1920 



BETTER FRUIT 



Page 13 



Temperatures Which Will Damage or Kill Fruit Buds 



By F. L. West and N. E. Edlefsen, of the Utah Agricultural College Experiment Station, Logan, Utah 



EXPERIMENTS conducted at the 

 Utah Agricultural Experiment 

 Station, to determine the tempera- 

 tures at which fruit buds receive injury 

 from being frozen, are both valuable 

 and interesting. These experiments 

 were undertaken to assist growers in 

 frost susceptible districts in the use 

 of heaters in their orchards and also to 

 know the drop in temperature neces- 

 sary to cause the lighting of the heat- 

 ers. Apart, however, from the value 

 of this knowledge to the grower who 

 may use heaters it is valuable to every 

 grower to know what degree of frost 

 will damage or kill fruit buds. 



During the first two years that this 

 work was being carried on the experi- 

 ments consisted in removing branches 

 from fruit trees and subjecting them to 

 freezing temperatures in the laboratory. 

 The damage done was then noted by 

 counting the buds that had turned black 

 and also the ones that were unaffected, 

 and thus calculating the percentage of 

 the buds that were damaged. As this 

 method did not give sufficiently definite 

 results, an apparatus was made for 

 freezing the entire tree. The yields of 

 the trees subjected to freezing tempera- 

 tures were noted at harvest time after 

 the buds on them had been checked up 

 at the time of the freezing or shortly 

 thereafter. 



The apparatus for freezing the trees 

 consisted of two double-walled half 

 cylinders made of galvanized iron fast- 

 ened to a wooden base that was put on 

 runners, by means of which the appa- 

 ratus could be moved by block and 

 tackle or team from tree to tree. The 

 cylinders were six feet high and six 

 feet in diameter in the clear. Four 

 inches of space was allowed for the 

 ice and salt. WTien the iron cover was 

 in place, ice and salt were spread over 

 it and then canvas thrown over the 

 whole to keep the heat out. 



As the ice and salt took the tempera- 

 ture down, thermometers projecting 

 through the sides showed the operator 

 the approximate temperature inside the 

 vessel. The temperature was modified 

 by forcing varying quantities of air in 

 at the temperature desired. This cur- 

 rent of air, together with an electrically 

 driven fan kept the temperature about 

 the tree uniform to within a degree. 

 Four standard minimum thermometers 

 were hung at various elevations on the 

 tree giving us accurately the minimum 

 temperature attained and a thermo- 

 graph also supported in the tree traced 

 out the temperature changes as it cooled 

 and then warmed up when the vessel 

 was opened up, thereby giving us the 

 rate of cooling and thawing. With this 

 equipment trees were subjected to 

 temperatures as low as 12 degrees Fahr- 

 enheit and by increasing the percent- 

 age of salt there is no doubt that tem- 

 peratures still lower could be obtained. 

 In making these experiments check 

 trees of the same size and kind with 

 approximately the same number of buds 

 and located near the frozen trees were 



selected. After the freeze, a certain 

 percentage of the buds were cut open 

 to observe the discoloration and the 

 same percentage were destroyed on the 

 check trees so that both trees were 

 thinned equally. The yields of both 

 trees were observed in the fall. To 

 note whether it made any difference 

 when the buds were examined, they 

 were cut open immediately after the 

 freeze and then at varying intervals 

 afterward. 



It will be of interest to make a little 

 study of the theory of the injury to 

 fruit buds due to freezing. 



^^^len plant tissue freezes water 

 passes out of the cells and ice forms 

 in the intercellular space. It has been 

 found that if the thawing is done slowly 

 enough when working with tender 

 plants, such as lettuce and matured 

 fruits, the water will gradually pass 

 back into the cells, and if the original 

 freeze did not rupture the cell wall, 

 the plant has suffered little harm from 

 the ice formation. If, however, the 

 thawing is done rapidly, the water does 

 not get back into the cells and they die 

 due to drying out. We must have then 

 either a rupturing of the cell wall when 

 the ice is formed or else ice formation 

 and in many cases rapid thawing in 

 order to kill the tissue. 



Pure water freezes at 32 degrees 

 Fahrenheit. When substances are dis- 

 solved in it, the water freezes at a lower 

 temperature, the amount of lowering of 

 the freezing point depending on how 

 much material is dissolved in it, and on 

 the nature of the substance that goes 

 into solution. For example, a five per 

 cent salt solution freezes at 27 degrees 

 F., while a thirty per cent sugar solu- 

 tion only freezes at 29 degrees F. W. 

 H. Chandler measured the freezing tem- 

 perature of the juice that he extracted 

 from twigs taken from various kinds 

 of fruit trees and found that on an aver- 



age the sap froze at from 28 to 29 de- 

 grees F. and in no case did it freeze 

 below 28 degrees F. The sap from 

 Elberta peach twigs extracted in March 

 froze at 28.7 degrees F., while but two- 

 thirds of the twigs of the same kind of 

 fruit when subjected in March to a 

 temperature of as low as 10 degrees F. 

 froze. 



In the orchard it is frequently found 

 that some of the buds withstand tem- 

 peratures as low as 20 degrees F. and 

 mature, and these buds no doubt take 

 up these low temperatures as the work 

 of Wiegend shows. 



Fruit buds have a protective cover- 

 ing over them supposedly for the pur- 

 pose of checking evaporation, but this 

 is not sufficient to keep them for any 

 appreciable length of time at tempera- 

 tures different from the surroundings. 

 Wiegend found as a result of experi- 

 menting with horse-chestnut buds con- 

 taining thermometers which he sealed 

 inside of them, that when these buds 

 were subjected suddenly to a change 

 in temperature of 20 degrees or more, 

 in about ten minutes they had taken on 

 the new temperature to within two de- 

 grees, and had arrived completely at the 

 new point in a half hour. In case of 

 the natural freezes in the orchard, 

 where the temperature is falling slowly 

 from sundown until sunrise, there is 

 little doubt that the fruit buds take on 

 the resulting temperatures of the sur- 

 rounding air. In artificial freezing 

 therefore it should not take long for 

 the buds to acquire the new tempera- 

 ture, especially if they are in full bloom 

 and when they are smaller than the 

 buds used in the experiment reported 

 above. 



As was mentioned earlier, the more 

 concentrated the aqueous solution the 

 lower is its freezing point and in gen- 

 eral the amount of the substance, espe- 

 cially if it be an organic one, that will 



Apparatus used in freezing entire tree in experiments niade at theJJtah Agricultural 

 Experiment Station, to determine the temperatures at which fruit buds are damaged 



by frost. 



