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“Winter Injury” on conifers

Discolored needles on evergreens, noticed in late winter or early spring. Causes are many, true cures are hard to come by.

Every year, starting in late February or early March, I begin to get calls and emails about evergreen trees that aren’t very green.  Some of the needles may be turning brown, red or even a shade of purple.  Generally, we categorize the problem as “winter injury”.  That’s somewhat vague, as the potential causes are many.

The classic example of winter injury is seen in the picture below.  All of the needles that are located above the snow are exposed to harsh winter conditions such as fierce winds and brutal cold.  Additionally, bright sunlight can reflect off the snow and create more problems. 

winter injury, conifer, evergreen, disease

The symptoms of winter injury in spruce trees are often somewhat different (below).  Needles turn different shades of purple or red or brown.  Usually, there is no specific pattern to the damage – the discoloration isn’t above the snowpack, or just on one side of the tree or even worse on one side.  It isn’t necessarily newer needles, or older needles, or needles on the tops of the twigs that are affected.  That makes diagnosis a little difficult – environmental problems usually show some type of pattern.  Nevertheless, if symptoms like these develop over the course of the winter, after January, then it’s almost certain that the problem can be categorized as winter injury. 

 spruce, conifer, evergreen, winter injury, stress, disease

While rough winter conditions can kill needles, the buds that contain next year’s growth often survive.  The trees in the first picture above were damaged in the 2009-2010 winter.  The shoots had new growth in 2010 and the trees recovered well.  Winter injury stresses trees and minimizing stress over the following growing season is important in helping trees recover.  Watch out for pests and treat them as needed.  Spruce trees that have been damaged by spider mites are more susceptible to winter injury than those that haven’t been attacked.  Minimizing drought stress is also important.  Make sure the tree has enough water to meet its needs, but don’t overwater.  A rule-of-thumb for watering is once every 10 days, if there has been no rain.  In the fall, watering up until the ground freezes will help keep the tree hydrated going into winter.  This will help to minimize winter injury, though it won’t completely prevent it.  Helping the tree to build new leaf tissue can also support its recovery.  Adding a small amount of nitrogen fertilizer in the spring – 1 to 3 lbs of nitrogen per 1000 square feet of soil surface – can help the tree to recover. 

Winter injury is common and reveals itself as dead needles during the spring.  Minimizing stress during the growing season can help trees recover from winter injury, and in some cases, can even lower the probability of winter injury from happening in the first place.

Joe Zeleznik

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