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Published April 10, 2009, 11:07 AM

How to handle winter injury to conifers

Many homeowners were concerned when the needles of red and white pines and some other conifers turned red or rust-colored this spring.

By: Jim Stordahl, DL-Online

Many homeowners were concerned when the needles of red and white pines and some other conifers turned red or rust-colored this spring.

The immediate assumption was that the trees were dead or dying. Although the needles look terrible, the buds, twigs and trees are probably not dead.

In an article in the Minnesota Department of Natural Resources’ Forest Insect & Disease Newsletter, DNR plant health specialists state that the needles had a rough winter and they were discolored by winter injuries.

Homeowners and landowners are cautioned to resist the temptation to get out the chain saw or severely prune these trees, because chances are good that these trees are alive beneath the mask of red needles.

Examine the needles carefully and you will probably find the tips of the needles are reddish or brown, while the base of the needles is still green. The buds at the ends of the branches will be soft and green and by now they are likely to be putting forth new growth.

This type of winter injury occurs when the needle temperature rises above freezing temperatures during sunny winter days. The stomata on the needles open and evaporation of water from the needles occurs. When the water stored in the needles, twigs and stems is gone, it cannot be replaced from soil water because the soil is frozen, causing the needle tissue to dry out and die.

The plant health specialists list last year’s drought, the lack of snow cover for much of the winter, deep frost in the soil, strong dry winds, many days of bright winter sunshine, and low relative humidity during the winter as contributors to the winter drying injury that we saw this spring.

If your conifers are showing some of these symptoms of winter desiccation, play the waiting game until late June. Water these trees by soaking them well every ten days or so, but do not fertilize them. If by the end of June there is no growth from the buds and the twigs become dry and easily broken, the tree, or part of the tree, is probably dead.

To help prevent winter injury in another year, keep conifers properly watered throughout the growing season and into the fall until the ground freezes. The recommended method of watering trees is to soak them well and then wait until the soil begins to dry and soak them again.

Waterlogged soil that may result from daily or very frequent watering may encourage root rot and add additional stress to the trees. Mulch over as much of the root system as possible with three to four inches of wood chips to help maintain soil moisture and to reduce the depth frost penetrates into the soil.

Conifers have had a rough winter. Fortunately, the native and hardy varieties have adaptations that allow them to recover.

For more information, contact me at the Polk County Extension office in McIntosh or at the Clearwater County Extension office on Wednesdays. Our toll free number is 800-450-2465, if e-mail is your thing, contact me at stordahl@umn.edu.

Source: Carl Hoffman, University of Minnesota Extension.

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