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May 20, 2004 Winter Injury Common in Spruce Trees This Spring Reports of spruce tree winter injury have been common and widespread throughout North Dakota this spring, according to Joe Zeleznik, North Dakota State University Extension Service forester. “The symptoms include whole or portions of needles with a brownish or purplish cast. Needles on the south side of the crown may be more affected than others, but this is not always the case.” A less-common pattern of winter injury is that the portion of the tree that was above the winter snow pack is dead, while the lower, insulated part of the tree remains green. Colorado blue spruce trees are more susceptible to winter injury than are Black Hills (white) spruce. The traditional belief is that spruce needles dry out on warm, sunny, windy days as they begin to photosynthesize. “However, dehydration may be more of a symptom than a cause,” Zeleznik says. “Cells in the needles may die simply because of extreme cold. Record low temperatures occurred throughout the state in late January.” Another mechanism is a loss of cold-hardiness following a mid-winter warm spell. In this situation, plants become accustomed to warmer temperatures and cannot tolerate as low a temperature as they did earlier in the winter. When cells in the needles die, the needles lose water and dehydrate. The needles then turn a brown or purplish color. The brown color caused by winter injury is somewhat similar to the color needles turn when infected with the fungal pathogens that cause Rhizosphaera needlecast or Cytospora canker. However, the patterns of these two diseases are completely different from winter injury. Rhizosphaera needlecast only affects older needles, not those from the most recent year. Symptoms of this disease may be noticeable in the spring and affect needles mainly on the interior of the tree. Symptoms of Cytospora canker appear as a uniform browning from the outside of a branch, which then moves toward the interior as water flow is restricted. Additionally, a tree may be infected with either of these diseases and still suffer winter injury. What can be done about winter injury? “The damage to spruce trees caused by winter injury is usually just an aesthetic problem and does not cause serious damage to the tree unless a large portion of the crown is affected,” Zeleznik says. “The one exception would be if the winter injury was severe enough to kill developing buds. This can only be accurately assessed when new growth emerges in the spring. Discolored needles will die and fall off throughout the spring and new growth will soon cover up the winter damage.” Preventing winter injury is very difficult. Watering trees late into the fall can help minimize damage but won’t completely prevent it. Also, it’s important that spruce trees not be watered in late summer. “This will allow them to go through their natural ‘hardening’ process in preparation for winter,” Zeleznik says. “Allowing this late-summer stress is a common practice in the nursery trade.” Anti-desiccants, applied coatings that create a waxy film, are sometimes applied to prevent dehydration over the winter. In scientific tests, however, the results have been mixed. For more information on winter injury of spruce trees, contact the NDSU Plant Diagnostic lab at (701) 231-7854 or Joe Zeleznik, NDSU Extension forester, at (701) 231-8143. ### Source:
Joe Zeleznik, (701) 231-8143, joseph.zeleznik@ndsu.nodak.edu |
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