April 16, 2001

•     Discoloration of Evergreens

Discoloration of Evergreens

    The winter of 2000-2001 has caused damage to many conifers (evergreens) in our area.  Reddish-brown, dead foliage in conifer trees is being seen in home landscapes, shelterbelts and other plantings.  This discoloration is usually the result of injury sustained last fall or during the winter that is showing up at this time, according to Marcus Jackson, forester with the NDSU Extension Service.  The extent of the injury will be determined when new growth occurs this spring.  As of this writing it is to early to assess the complete damage.
    Winter injury is due to the desiccation of leaf tissue through the exposure to wind, temperature and sunlight.  Winter injury can also be caused by the tree not being acclimatized (to adapt to a new temperature or environment) due to sudden changes in weather conditions.  The combination of lack of acclimatization, temperature extremes, wind and sunlight, could all have caused the symptoms we are now seeing.  Using weather data from the NDAWN stations at Dazey and McHenry, I looked for conditions that might have caused poor acclimatization, temperature extremes and high wind events.  The following is what was recorded from October 1, 2000 to March 1, 2001.  
    Acclimatization possibilities:  The Dazey and McHenry stations recorded the following data for ten days prior to November 6th and ten days following November 6th:                                                  

 Notice the drop in maximum and minimum average temperatures during this period.  November 6th and November 7th time period is where the temperature change took place.  On November 5th, there were Maximum temps of 54 and 50 and  Minimum temps of 34 and 32 at Dazey and McHenry respectively.  On November 8th there were Maximum temps of 21 and 19 and Minimum temps of 18 and 15 respectively.  Temperature conditions that averaged above freezing dropped to below freezing in the matter of two days.  This drop might have occurred too fast for the trees to become a custom to freezing temperatures.  As winter progressed into December, temperatures dropped to the coldest period of the winter.  Throughout most of January there were mild temperatures along with sunny days.  The following table shows the temperature averages over December and January:

The white snow cover, sunny days combined with the fluctuating temperatures and windy conditions, made for ideal conditions for winter injury. The extent of the injury will be determined if there was any major bud damage.  Once bud break occurs, the fate of the tree can be determined.  The following pictures will show some of the damage.  I will also be watching these trees as they progress throughout the season.  

                     Click on Photos to enlarge

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