Freeze Damage to Spruce

Many spruce trees in the area are looking rough. Beyond the usual injury from spruce spider mites and Rhizosphaera needle cast, spruce trees have serious dieback, not only individual branches but in some cases, the top has died. Drooping clusters of brown needles and streaks of white sap on branches and trunk indicate freeze injury.

While late April is our last average frost date, early May saw a deep drop in temperatures, bringing with it freezing cold and frost. Much of the new growth in spruce trees was damaged by this cold spell. While spruce trees are well-suited to cold temperatures, new growth is not. New twigs and needles develop thickened cell walls (called lignification) as they mature, needing the bulk of the growing season to complete this process. Spring’s new growth simply didn’t have enough time to toughen before the cold hit, resulting in collapsed tissues and death to ends of branches. While these dead areas will eventually fall away, pruning out dead twigs and needles can also be done.

freeze damage on spruce 2, image from M. Eldal

The same weather conditions brought about the white streaks of sap on tree trunks and branches. As spring weather warms the atmosphere, sap flow rises from tree roots, bringing much needed water, nutrients, and stored sugars, distributed throughout the tree. Freezing cold will cause the water in sap to freeze, bursting cell walls and subsequently cracking the bark. Sap leaks from these wounds, eventually turning white as it drips down the trunk and branches. Often, secondary infections take place, with Cytospora fungal pathogens entering wounds and expanding damage to water-conducting tissues. In some cases, the top of the tree dies completely.

When the central leader of spruce and other conifers die, the form of the tree can be salvaged by re-establishing a central leader. The dead leader is cut away and a side branch is gently curved upward and secured to a stake placed along the trunk. Staking materials must be removed in one year to keep materials from causing further damage to the tree.

There isn’t anything to counter freeze damage and the resulting Cytospora infection. While tree owners want to help, fertilizing these trees should not be done as this deepens tree stress. Practicing good tree care is an excellent step: water deeply during dry spells, mulch with 2-4 inches of wood chips, and refrain from using any herbicides containing dicamba anywhere near trees. By practicing good tree care, the tree’s own defenses are enabled to weather setbacks.


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