47 



Although an extremely low temperature is an important factor 

 in causing winter injuries, yet, extreme variations in temperature, 

 lack of moisture in the soil, high winds, the kind and variety of 

 tree and its condition are all of much consequence. 



The weather conditions, during the late summer and fall and 

 just preceding winter should never be overlooked in investigating 

 any case of winter injury. 



It is a commonly stated fact that a late, sappy wood growth is 

 responsible for the severity of winter injuries to our fruit trees. 

 This is undoubtedly true in numerous instances, especially in the 

 extreme northern fruit districts, but it is equally true that a se- 

 vere drought and sudden check in the development of the trees, in 

 the late summer and fall, may result in winter injuries equally se- 

 vere. This latter fact has been generally overlooked in emphasizing 

 the importance of well ripened wood to withstand the winter. 



Evaporation takes place from the branches and twigs of trees 

 and shrubs throughout the winter, and if one will but examine the 

 twigs of fruit trees following a very cold, dry period, the bark of the 

 twigs will appear to have lost some of its brightness and fullness 

 and may even be slightly shriveled. If the cold, dry period is fol- 

 lowed by rain and high temperatures the bark on these same twigs 

 will become much brighter and more full. The tree has taken up 

 more moisture and it is indicated in the appearance of the bark. 



Serious injuries are certain to occur to fruit trees whenever the 

 soil freezes to the full depth of the root system, followed by a con- 

 siderable period of dry, cold winds. The twigs and branches of the 

 trees may be actually frozen dry, especially if the soil was dry pre- 

 vious to freezing. 



Apple trees in full bearing are sometimes killed outright, in a 

 single winter, in the Dakotas and in some of the provinces of Can- 

 ada. Root injuries are caused by low temperatures and by alter- 

 nate freezing and thawing of the roots. Such injuries are quite 

 common in extreme northern fruit districts, and are most severe 

 in those localities when the soil is dry and the ground free from 

 snow, during cold periods. 



Experiments conducted by the Nebraska Experiment Station 

 are of much interest in this connection. Fruit trees were planted in 

 boxes, containing different amounts of moisture ranging from 15 to 

 25 per cent, just before winter. Some also received a straw mulch, 

 others were covered with snow whenever snow fell, and some were 

 stored in a cool dry cave. More than sixty per cent, of the trees 

 died in the boxes where the moisture content was 15 per cent. Less 

 than 15 per cent, of the trees died where the moisture content was 

 19 per cent. Not a single tree died in the boxes mulched with straw, 

 although the moisture content was only 16 per cent. Some trees 

 died in the boxes that were occasionally covered with snow and 

 whose moisture content was 15 per cent., but the injury was much 

 less than in the uncovered boxes containing the same amount of 

 moisture. 



