Winter Damage to Trees and Shrubs

This season's cold, snowy winter has been difficult for plants, wildlife, and humans. Extensive damage to landscape plants has been observed across the entire state.

Wildlife Damage

Symptoms: The deep snow and extended period of snowcover have posed serious problems for wildlife in the state. Denied access to food on the ground, rabbits and deer have been forced to feed on unprotected trees and shrubs in windbreaks, home orchards, and landscape plantings.

Rabbits have gnawed off the bark on many young, thin-barked, deciduous trees. Damage has been most extensive on crabapples, apples, serviceberries, plums, cherries, willows, and honeylocust. On many trees, the bark has been removed completely around the trunk, effectively girdling them. Rabbits also have fed on deciduous shrubs. Extensive damage has been observed on winged euonymus (burning bush), sumacs, dogwoods, cotoneasters, viburnums, roses, and spireas. The rabbits have debarked large stems and snipped off small twigs. Arborvitae, pines, and other evergreens also have experienced damage. Rabbits have stripped off the foliage on the bottom portion of large evergreens, while smaller evergreens have had their tops gnawed off.

Deer have been another threat to trees and shrubs in the state. Arborvitae, pines, and other evergreens have been victims of deer browsing. All the green growth on some evergreens have been stripped off as high as the animals could reach.

Prognosis: Trees that have been completely girdled have essentially been destroyed. Wrapping the trunk or applying pruning paint to the damaged area will not save the tree. Most affected trees will sucker from the base. However, since most fruit and ornamental trees are propagated by grafting, suckers which originate from the rootstock will not produce a desirable tree.

Many deciduous shrubs have the ability to produce new shoots or suckers at their base. Because of this ability, many severely damaged deciduous shrubs will eventually recover. (It may take some shrubs several years to fully recover.) Girdled stems should be cut off just below the feeding injury.

The key to the condition of damaged evergreens is the presence of growing points or buds on the injured branches. Branches that have had all their buds devoured by hungry animals will not produce new growth this spring. As a result, some small evergreens may have been completely destroyed. Larger evergreens may have permanently lost their lower branches. Since buds on arborvitae and junipers are difficult to see, individuals may want to wait until spring before taking any action. Branches that don't produce new growth by mid-June have been destroyed and can be removed.

Brown Evergreens

Symptoms: The needles on many evergreens have turned brown in recent weeks. The browning of needles on evergreens is generally attributed to winter injury. The damage is thought to be caused by a combination of desiccating winds, winter sun, and widely fluctuating temperatures. The dry conditions that have prevailed over large areas of Iowa over the past two years may also have played a role. While the browning of needles normally shows up in March and April, this winter it began to appear in January. It has become progressively more widespread over the last few weeks. Browning of evergreen foliage can be seen on pines, yews, arborvitae, firs, and spruces. Damage is most evident on the south and west sides of trees and shrubs.

Prognosis: The brown needles on affected trees and shrubs have been destroyed and will eventually fall off. Fortunately, the buds on most damaged evergreens are still alive and will break bud and produce new growth this spring. The affected trees and shrubs should look much better by late June or July. There is no need to fertilize affected evergreens. However, if the weather this spring is dry, periodically water the trees and shrubs to encourage new growth and speed their recovery.

This article originally appeared in the March 9, 2001 issue, p. 21.

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