Pests AND environmental PROBLEMS of High Altitude Landscapes

Jessica Hendryx B.S. in Horticulture Science with a Landscape Design Option ~ Montana State University, Bozeman

Frost Cracking of Deciduous Trees

The characteristic symptom is the long vertical crack down the main trunk of the tree. At first glance it may appear that lightning has struck the tree. The cracks down the trunk commonly occur on the south to south west side of the tree where the afternoon sun is the strongest. They can be several feet long and several inches wide, the colder the temperature the wider the cracks. A callus may be formed around the edges of the crack if it is a commonly occurring problem. Calluses are a plants response to heal when it is injured.

Frost cracking is caused by the drastic changes in winter temperature. The tree trunk may be warmed up to 18 degrees (F) above the air temperature. On a warm winter day and a cold night this temperature change can be very drastic. Uneven contraction of the wood cause the trunk to crack. The crack usually occurs in the bark and wood parallel to the grain and extends to the center of the trunk (See Figures A &B). 

Once a frost crack has occurred it is likely to occur again. The cracks commonly open each winter and close in the spring, occurring on the same crack line each year. This problem can form a considerable sized callus along the crack edges and wood decay may begin. However, generally it is only cosmetic and does little damage to the tree. It is common on the hardwoods, such as Green Ash and Burr Oak, and has limited preventative maintenance. It is best to leave the tree be and accept this crack as a part of nature.  

 

Sunscald of Deciduous Trees

Sunscald is very similar to frost cracking in that the extreme temperature conditions affect the plant and the problem is generally located on the south to south west side of the tree. Sunscald commonly occurs in the high altitude landscapes during the late winter to early spring. The warm afternoon sun warms the bark up enough to deharden the cells that were hardened off for the winter months. The rapid drop in the evening temperature kills these cells that are now susceptible to problems because they have been dehardened. Long dead strips of bark peel off and expose the sapwood (See Figure C).  

The placement of the trees is an important in preventative maintenance. Place trees that are highly susceptible, which include trees with dark, smooth, and thin bark away from direct sun or next to a building. Any area that has the potential to heat up drastically during the day can be a problem. Carefully select the correct species for your area. This will limit the likelihood of the sunscald occurring on the landscape trees. Plant evergreen shrubs around susceptible trees to help shade the tree bark during the winter which will help reduce sunscald.

Smooth Bark Trees: Mountain Ash, Apple, and Maple                                          

Dark Bark Trees: Cherry, and Green Ash

If the tree is in a problematic area the trunk can be wrapped in a white tree wrap, such as heavy kraft paper or burlap. This covering will not insulate the tree, but will help to reflect the light that would normally heat the trunk. Wrap the trunk from the soil line to the lowest branch in the fall and remove the wrap in the spring.    

To find out more: http://gardenguide.montana.edu/priorocts/october99.htm

Figure A: Frost Cracks on Green Ash (southwest side)

Figure B: Frost Crack on Green Ash (southwest side)

Figure C: Sunscald on Apple Tree

 

References:

Gough, R. What's Wrong With Tree? Montana State University Extension Service:1999

Harris, R.W. Clark, J.R. Matheny, N.P. Arboriculture. Prentice Hall:1999 pg 64

 

Montana State University Extension Service 
Designed and researched by Jessica Hendryx - B.S. in Horticulture with a Landscape Design Option
For problems or questions regarding this web contact [martha@montana.edu].
Last updated: April 24, 2002.