496 



CALIFORNIA FRUITS: HOW TO GROW THEM 



SUSCEPTIBILITY OF DECIDUOUS FRUITS 



The most systematic observations of danger points in deciduous 

 fruits have been made by Dr. J. C. Whitten and Professor W. L. 

 Howard in the course of their work at the Missouri Experiment 

 Station. Both these experts are now connected with the California 

 Experiment Station at Berkeley and the local bearing* of their re- 

 searches may be had from them by any one interested in the subject. 

 Their work in Missouri involved artificially freezing thousands of 

 peach buds, from which these conclusions were drawn : 



"Fully dormant peach buds can stand 8 or 9 below zero, F. When they 

 are appreciably swollen, zero is the danger point. When the buds are show- 

 ing pink, they can stand 15 above zero. When the buds are almost open, 

 25 is the danger point. When they are newly opened, about 26 would be 

 the point of danger. When the petals are beginning to fall, 28 above zero 

 is dangerous. When the petals are off they can stand 30 above zero. When 

 the 'shucks' (calyx lobes) are beginning to fall off, 32 is the danger point." 

 Presumably these limits would apply also to the apricot and almond. 



Apple buds, when the petals begin to show, can stand from 10 to 12 de- 

 grees of freezing. When the petals are well emerged, but have not opened, 

 they can stand from 4 to 6 degrees of freezing, but when open, but not yet 

 fertilized, there would be great danger at two or three degrees below the 

 freezing point. When the flowers have been fertilized, the petals dropped, 

 and the young fruit increasing in size, the slender stems which support the 

 apples are unable to resist a temperature lower than the freezing point. The 

 apples seem to be more hardy than their stems, but if the latter are injured of 

 course the fruit also suffers. Similar behavior may be expected from the pear, 

 cherry and plum. 



Orchard Frost Studies. In connection with the foregoing it is 

 interesting to note conclusions which Prof. Fabian Garcia draws 

 from several years' observation of frost effects in the orchard of the 

 New Mexico Experiment Station and of which full details are given 

 in Bulletin 89 of that station : 



The data recorded at the Station show that the fruit-buds, particularly 

 those of the peach, at their different stages of development are somewhat 

 more resistant to cold than has been reported by observers from other 

 parts of the United States. The data further show that the degree of re- 

 sistabihty to frost varies with different stages of growth. 



The peach is least resistant when it is about the size of a pea, when the 

 calices are falling off. Contrary to the findings of other observers, the 

 bloom is not the most tender stage of growth. In other words, the data 

 indicate that the newly set peach is more delicate than the newly opened 

 blossom. 



In the majority of cases a temperature of 26 degrees, lasting only a 

 short time, did little or no injury to the opening bud, newly opened 

 blossom or newly set fruit of the peach, native plum, pear and apple; 

 while one-half a degree below this or 25^2 degrees, although lasting only 

 a few minutes, killed a large percentage of the opening buds, newly set 

 blossoms and young fruits of the peach, in a number of cases. In other 

 words, 26 degrees was the danger point, and any temperature below this 

 is liable to do more or less injury; depending on how low it gets and 

 how long it remains at that temperature. In some cases, however, a 

 temperature of 24 degrees lasting only a short time left about 25% of 

 the blooms and 9% of the newly set fruits uninjured. 



Three important factors that influence the amount of damage done by 



spring frosts are: the degree of killing temperature, the time of day at 



h it occurs, and the length of time the temperature remains below the 



danger point. The longer the time the killing temperature remains and the 



