Recognize and give help to stressed trees

July 22, 2004
Victoria County
Master Gardener Intern

Trees are near and dear to us due to their majestic, stately appearance and aesthetic value, so we notice when something is not right with them. We need to be able to recognize the sick, stressed tree syndrome. Normally, stress to trees can result from short- or long-term exposure to environmental or cultural factors.

Healthy trees have a large supply of stored nutrients, which enable them to survive for several years following either continual or intermittent exposure to stressful conditions.

How long a tree can survive under these conditions depends on the health of the tree when it is exposed to the stress; tree species; total number of factors acting on the tree; and severity of injury.

If stresses continue, the tree will produce less food reserves than normal. In time, there will not be sufficient energy in the tree to force out a major flush of buds in the spring.

During the early years of tree stress, although the growth rate is slowed, the tree may appear to be healthy. As stresses accumulate, twig growth diminishes from 8 to 12 inches per year to 2 to 3 inches or even less. Leaves become fewer and one can see through the canopy more easily. In the final stages, only small groupings of leaves remain and the tree is weak, giving off a chemical odor that attracts tree borers and predisposes it to insect and diseases.

The first corrective step is to identify the cause, realizing that the tree may take five to 10 years to recover, or may be beyond the point of recovery. Practices used to overcome tree stress have best results in early stages of tree decline with better response from a stronger tree.

Location of tree roots is important. Undisturbed roots of mature trees extend out from the trunk 2.5 to 3 times the distance from the trunk to the tree's drip line. Most trees have roots that extend several feet below the soil surface. Heavy, dense clays in the top two feet restrict many tree roots in our area, causing most feeder roots to be in the top 8 to 16 inches. Activity over this root area impacts tree health.

Many landscape plants also develop dense roots that compete with trees for moisture, space and nutrients. Removing some of this plant material (even turfgrass) from over the tree's root area may help. Once removed, mulch as much of the soil above the root zone as possible to a depth of 3 to 4 inches. Leave several inches of space between the mulch and the trunk of the tree to prevent trunk crown decay. Do not use a heavy layer of mulch if you have heavy clay soils and your landscape stands in water with frequent rains. It will keep the soil too wet and void of oxygen. In that case, periodically apply a simple quarter-inch to half-inch layer of mulch applied .

Determine if water is being trapped in the tree's root zone. Oxygen is depleted from trapped water, and roots cannot survive. If water is standing, soils remain excessively wet or obstacles block water flow, redesign of landscaping may be required.

Irrigation should be on an "as needed" basis. Check the soil at 6 to 8 inches depth to determine moisture using the feel method. In clay or loamy clay soils, if there is enough moisture to form a ball or ribbon when squeezed between the thumb and forefinger, delay the watering for a few days. Sandy soils will not ribbon or form a ball, but will have a moist feel to the hand. Do not allow soils to dry to the extent that plants wilt or leaves start dropping.

Develop a landscape design that reduces foot or vehicular traffic over a tree's root area. Walking, driving, remodeling or construction work can cause soil compaction and result in poor root growth. Aerate the soil if compaction is suspected. Use stepping stones or mulch to form walk ways and avoid compaction.

Do not apply soil over the root area of the tree. This can prevent gas exchange and water movement into the root area, resulting in root loss. If soil is applied, the old roots will die and new roots will have to be reestablished at a new level. If you must raise the soil in the root zone area, add only 1 to 2 inches of soil per year. Excessive soil additions will kill roots and may weaken the tree to the point of death, usually in three to six years.

Pruning of a stressed tree should be restricted to dead, broken limbs or limbs that present a hazard to individuals working around the tree. Excessive pruning removes leaves and deprives the tree of the energy the leaves would have produced. Pruning is necessary to maintain a healthy tree. However, trees are often pruned for aesthetic appearance and not for tree health.

In some cases, a tree may have declined to such extent that it would be best to remove the tree and start over with a new one. This will reduce the liability of a weak tree in your landscape, improve family safety and increase your property value.

Proper care of trees involves being aware of the functions of each part of the tree and seeing that those parts are not hindered in "doing their thing." The best stress management program for trees is to prevent the problem from happening. More detail on tree care, pruning, fertilization, etc. may be obtained from the Victoria County Extension office.

Or better yet ... a full session will be devoted to working with trees for the home and Victoria soils in the Victoria County Master Gardener Association fall training course beginning on Aug. 12. Consider branching out your gardening knowledge on trees and various other subjects with other trainees this fall. Call the extension office at 361-575-4581 for more information and a class application.

Registration deadline is August 2.