LEAF DISEASES AND INJURIES 21 



Late Frost-Injury 



Caused by low temperatures in the spring 



Low temperatures in the spring, after new growth has 

 started, often result in what is commonly known as late frost- 

 injury. This type of injury is especially noted on conifers. 

 The young growing tips of the branches, with the newly unfolded 

 succulent leaves, wilt, die and turn brown. Sycamores and 

 other deciduous trees which start their growth early also are 

 often injured by low temperatures in the spring. In the case 

 of the sycamore, the symptoms of late frost-injury and the 

 anthracnose disease (see page 333) are often confused. The 

 injury caused by late frosts is due directly to the freezing-to- 

 death of the susceptible succulent growth. The tissues of the 

 growing tips of the twig and the young unfolding leaves are the 

 most susceptible of any of the tissues of the tree. Only a 

 very slight fall of temperature below the freezing point is 

 sufficient to cause the withdrawal of enough water to result in 

 death. For a more detailed description of the effects of low 

 temperatiu-es in causing freezing-to-death, see page 12. 



Injury from late frost usually occurs on south slopes and in 

 badly drained hollows known as frost-pockets. By planting 

 susceptible species in locations usually free from frost and not 

 exposed to the direct rays of the sun, a large part of the injury 

 caused by late freezing may be avoided. Other methods of 

 retarding the growth in the spring will also furnish some pro- 

 tection. 



References 



Schrenk, Herman von. On frost injuries to sycamore buds. Mis- 

 souri Bot. Garden Ann. Rept. 18 : 81-83, pi. 7. 1907. 



Morse, W. J. Winter injury of the white pine in 1908. In Notes on 

 plant diseases in 1908. Maine Agr. Exp. Sta. Bui. 164 : 21-28, 

 fig. 4. 1909. 



