You may be prepping yourself for “the call” … the one where the customer just starts describing a malady on their tree that wasn’t there in late fall. Especially after a drought, this is a likely scenario. Unfortunately, these calls will not be rare, easy to fix or linked exclusively to the drought — quite the contrary. As a tree professional, your job is to determine what happened and how to provide the best solution. Fortunately, in many cases, a positive course of action can be devised that provides both good tree care and profits for your business.

The symptoms of callus formation and graying heartwood indicate that this is an old injury, not recent winter damage. Photo: John C. Fech, UNL

The symptoms of callus formation and graying heartwood indicate that this is an old injury, not recent winter damage. Photo: John C. Fech, UNL

Distinguish from other damage

Determining the exact cause of the damage that occurred over winter can be difficult. Two indicators can be helpful in the quest to discover the cause: the uniformity of the appearance of the injury, and how long the signs and symptoms have been evident.

Though not always the case, winter injury tends to be uniform, at least at first glance. Since winter injury usually occurs due to an abiotic factor, it’s common for one side or a localized portion of the tree to be affected rather than the entire tree, such as in the case with pathogenic diseases or insect-related causes.

The symptom of a “fresh” injury is another key to distinguishing winter damage from existing maladies. Winter injury takes on a certain look that speaks out as if it just happened, as opposed to the grayed, dull appearance of older instances of insult to the tree. Tree tissues that are dried out, softened or responding to the injury in an attempt to compartmentalize the wound are good indicators of damage that has been present for a growing season or longer.

Sunscald causes a major disruption in cambial flow. Photo: John C. Fech, UNL

Sunscald causes a major disruption in cambial flow. Photo: John C. Fech, UNL

Types of winter injury

One of the most obvious winter injuries is desiccation, caused by a drying of the leaves, stems or roots. Most common on evergreens such as arborvitae, yew, pine and spruce, desiccation is most commonly caused by winds passing across the tissue surface repeatedly. Without sufficient protective layers in place, the inner cell sap evaporates, or is simply removed, and the remaining tissue turns from green to brown.

A common winter injury of deciduous trees is sunscald. During winters where intense sun causes a warming of the trunk bark on the south and west side of the tree, these tissues soften during the day. When cold temperatures return at night, the tissues are damaged slightly due to the warming/cooling cycle. Though not always the case, damage from sunscald seemingly occurs more often on thin-barked trees, such as red maple and white ash, in the first 10 or so years of growth. Several options exist for prevention of sunscald from placing a protective collar in place to painting the trunk with white paint to reflect the winter sun.

Mice, voles, squirrels and rabbits can cause extensive damage over winter. As these critters search for food, a tree trunk is commonly determined to be suitable, especially when other food sources are covered with snow and ice. The protective collars mentioned above are effective in reducing feeding damage as long as they cover the majority of the trunk surface.

Winter storms are one of the most frustrating forms of winter injury, as there are few preventative measures that can be taken to reduce it, yet the potential for significant injury remains high. When winter winds or extensive snow loading cause branches to bend beyond their capacity, the result is often breakage. In addition to the removal of necessary photosynthetic surfaces, limb breakage exposes inner tissues that are prone to decay, potentially causing a sturdy tree to change into a hazardous one, depending on where it is located on the property.

Breakage from a storm. Photo: John C. Fech, UNL

Breakage from a storm. Photo: John C. Fech, UNL

Especially in the North, construction projects are usually delayed until temperatures are conducive to ease in soil movement and manipulation in spring. However, in some cases, such as water line breakage, repairs must be made in winter, causing a severing of the root system and compaction of soil particles. These insults are injurious at any time, but when they occur in winter, the tree is less able to prevent drying and begin compartmentalization of the wounds.

In addition to the causes of winter damage that are due to definable factors, there are maladies that occur due to unknown forces, or a combination of the causes mentioned above. In these cases, the only real information that is available for assistance with diagnosis is that the tree was in good health in the fall, and in the subsequent spring it appears differently. Though it may not provide much solace in times of frustration over diagnosing these problems, consider that approximately half of the tree is underground, out of view, and may be more related to issues such as girdled roots or deep planting than winter damage.

Recovery

Recovery from winter injury is directly tied to the cause of the damage. Unfortunately, in many situations, recovery steps involve minimizing the appearance of the symptoms and practices intended to prevent further damage instead of actions that will instantly cause the tree to improve.

Desiccation on tree tissues with a history of damage can be prevented, or at least lessened, through applications of horticultural wax products in late fall and during periods when temperatures exceed freezing. For the best results, these products should be applied every five to seven weeks and allowed to dry during daytime hours before freezing temperatures return in the evening. Trees with a high level of importance can be screened with burlap or plastic sheeting to reduce the effects of damaging winds. Once the leaf tissue has dried out, not much can be done to replace it. Corrective action is based on removing affected areas, making pruning cuts back to viable buds and green tissue.

When you think of winter damage, you think of desiccation. Photo: John C. Fech, UNL

When you think of winter damage, you think of desiccation. Photo: John C. Fech, UNL

Recovery from feeding by unwelcome animals is similar to dealing with desiccation. In an urban area, choices for directly reducing the critter population are usually strongly restricted, leaving protective devices as the main course of action. When placing protective collars around trees several factors should be considered. First, the material should be tough enough to resist feeding by the animal, yet sufficiently flexible to prevent damage to the trunk. Collars made from PVC provide this balance better than other materials like kraft paper, vinyl wrappings and steel plating. Secondly, the collar should be a light color to reflect the warm solar rays, keeping the bark temperature as even as possible during the day and nighttime hours. Finally, the collar should protect the entire distance of potential damage, from the lower limbs to several inches into the soil.

Storm breakage recovery is mostly a matter of removing the broken limbs from the property and making clean cuts on the tree trunk to allow the tree to begin the isolation or compartmentalization process. In many cases, especially when the damage occurs close to or in the trunk, some level of uneven bark and heartwood cannot be prevented. When breakage occurs in the middle of a limb, using the traditional three-cut method works well to encourage recovery.

Winter construction projects can cause injury through root severing and compaction. Photo: John C. Fech, UNL

Winter construction projects can cause injury through root severing and compaction. Photo: John C. Fech, UNL

Removal and compaction of soil in winter can cause serious stress, depending on the size of the affected area. A positive recovery step is to make clean cuts on the roots that were torn or shredded from the construction equipment. Of course, in some cases this is not possible, as new or existing soil is placed over the damaged roots soon after the injury occurs. Yet, if feasible, this type of recovery step is one to endeavor to make.

Recovery from an unknown cause of winter damage is difficult to prescribe. However, in many situations, providing good plant health care and best management practices is a step in the right direction. The steps of proper mulch placement, soil aeration, separating turf from ornamentals/trees, keeping the soil moist but not dry or soggy, soil testing to determine nutritional deficiencies, placing trees where they have sufficient room to grow well, choosing disease-resistant trees, and planting trees in such a way that the uppermost roots are at or slightly above soil grade will go a long way towards assisting your customers in concerns of an unknown nature.