Frost and the Prevention of Damage by It. 39 



stage may kill all or most of the more advanced blossoms, there may 

 still be a sufficient number of unopened buds left to insure a crop 

 of nearly normal size. However, fruit from late bloom is usually 

 undersized and of poor quality. 



In the process of natural thinning the number of fruits on the 

 trees is steadily and rapidly reduced after the period of full bloom 

 and the loss of a large percentage of the fruit retained on the tree 

 at this time is likely to reduce seriously the size of the crop harvested. 



It is obvious from the above that the greatest need for protection 

 comes after the period of full bloom. While a single night's frost 

 during the period of full bloom may not seriously reduce the size 

 of the final crop of apples, peaches, apricots, or pears, when the 

 amount of bloom is reasonably heavy, each one of a series of heavy 

 frosts at this period may kill a certain portion of the remaining 

 uninjured blossoms, until not enough sound blossoms are left to make 

 a full crop. Where an orchard is equipped with heating devices 

 the only safe policy is to hold the temperature high enough at all 

 times so that only a few blossoms will be injured. 



Apples and pears are often badly injured by frost but remain on 

 the trees and mature. Such fruits are mis-shapen and more or less 

 seedless and are not marketable as first grade. Frosted pears enlarge 

 abnormally near the stem and lose their characteristic pear shape, 

 while injured apples become rough and their shape irregular. In- 

 jured fruit of this kind often remains on the trees until a month be- 

 fore maturity and then drops. 



The blackening of the centers of blossoms or of small apples and 

 pears does not necessarily mean that they will not mature, though the 

 cha-nces are greatly in favor of their dropping before the end of the 

 season. The injured tissue is often gradually absorbed until the 

 blackening entirely disappears. 



Different varieties of the same fruit often differ considerably in 

 degree of resistance to frost damage and when the same critical tem- 

 perature is given for all varieties, it is applicable only in a very gen- 

 eral way. The best possible arrangement to be followed by the 

 orchardist who protects his orchard is to keep in touch with the local 

 county agricultural agent or horticultural commissioner as the season 

 progresses and obtain opinions from him from time to time as to the 

 temperatures that will cause damage. These officials are likely to 

 have had considerable experience in noting the effect of low tem- 

 perature in the local district and are also familiar with the condition 

 of the fruit or blossoms as they have been affected by previous 

 weather conditions. 



It will pay the individual grower to keep careful records of the 

 temperature in his orchard on cold nights, together with notes on 



