Evidence of Soil compaction
1. Smaller than normal leaves.
2. Reduced twig (new shoots) growth.
3. Early leaf drop.
4. Overall low vigor, branch tips dying.
5. Decay in trunks and branches (fill in holes with poly insulating foam)
HELPING STRESSED TREES RECOVER
JERRAL D. JOHNSON AND DAVID N. APPEL
Stress can result from many different factors.
1. Soil compaction
2. Poor drainage
4. Fill soil
5. Excavation over the root area
6. Low fertility
7. Competition with other plants for nutrients and water
8. Excessive salts from irrigation water or fertilizer
9. Defoliation due to leaf feeding insects or foliage diseases
10. Soil fungi reducing effectiveness of roots
11. Insect bores
12. Minor element deficiency
13. Tree species not adapted to climatic conditions or soil type
14. Temperature extremes
15. Herbicide injury
Stress can result from short or long term exposure to one or more 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 following exposure to the conditions, depends on health of the tree when exposed to the stress, tree species, total number of factors acting on the tree and severity of injury. Trees that are under stress can be compared to a bank account that has $10,000 dollars. The owner of that account removes $1,000 each year to live on but only deposits $900 each year. At the end of ten years there will be less than a $1,000 dollars in the account. Generally this is what happens to a tree that is under stress. Each year due to reduced root and leaf activity, there will be less food that there was the year before. In time there will not be sufficient energy in the tree to force out the buds in the spring. During the early years, although the growth rate is slowed the tree appears to be healthy. As the bank account become less, the tree begins to show symptoms of decline, It's leaves are smaller, lighter green in color and there is less and less growth. Practices used to overcome the stress factors are most effective if they are utilized during the early stages of decline. The weaker the tree, the less likely it will respond to treatment.
Easily transplanted trees are more likely to recover from conditions that cause root injury than trees that are difficult to transplant. In a short period of time they re-establish roots loss to adverse soil conditions. Post oak is a species that is almost impossible to transplant and is especially susceptible to stress.
The first step to correcting the problem is to identify the cause. Location of tree roots is important with diagnosing potential problems. The undisturbed roots of mature trees extend outward from the trunk a distance of 2.5 to 3 times the distance from the trunk to the tree's drip line. Root distribution of transplants is less than a mature tree. Most trees will have roots that extend several feet below the soil surface unless the soil or rock restrict spread. However, most feeder roots are in the soil's top 8-10 inches. Activity over the root area impact overall tree health. Once the problem has been identified, develop a plan to correct the causes and take steps to recover. In some instances, the tree may be beyond the point of recovery.
Steps to Identifying and Correcting Stress Conditions
1. Remove plant material from over the tree's root area. Many landscape plants develop sensor roots that compete for moisture, space and nutrients.
2. Mulch as much of the soil above the roots as possible. Mulch to a depth of 3-4 inches. This will be sufficient to prevent weed and grass growth. The mulch will also help to maintain a more uniform soil moisture level. Mulches also help to maintain lower soil temperatures that are more suitable for root growth. Root tips of many plants are killed when exposed to a temperature of 104 F for 4 hours. Root growth of black locust was reduced by 75% when exposed to 95 F for 6 hours on 4 consecutive days.
Place a collar around the trunk to prevent the mulch from touching the trunk and causing decay. There needs to be a few inches between the collar and the trunk. Flexible material should be used for the collar. The collar must expand as the tree grows or be biodegradable. If it does not expand, it can girdle the trunk. A collar should also be used if a flower bed is placed around the base of a tree.
3. Determine if water is being trapped in the tree's root zone of the trees. Oxygen is depleted from trapped or standing water. Roots can not survive in this situation. Remove the water by installing French or other drain types.
4. Water that stands on the surface should be removed if it consistently remains on the surface for several days following rain or irrigation. Remove obstacles that might be blocking water flow. This may require redesigning the landscape or installing drains.
5. Irrigation should be on a need basis and not on a set schedule. Check the soil 6-8 inches below the surface to determine the presence of water in the soil 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 fore finger, 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. When irrigating large trees, the critical area is several feet on either side of the drip line. Most feeder roots are located in that area. Wet the soil to a depth of 6-8 inches. A slow application of water is suggested. Water applied too fast wets only the top one or two inches and then runs off. Soaker hoses that drip slowly are excellent. However, if too much pressure is applied, the hose splits. This results in uneven application of water, run off and wasted water. Commercial drip irrigation lines are available and are effective and do not split as easily as the soaker hose. They are more expensive and storage is difficult.
6. Mature live oak trees should receive sufficient fertilizer to maintain a growth rate of 5-7 inches of annual growth. Tree species vary in their annual growth rate. Check with arborists, nurserymen, County Extension Agents and other professionals on what would be a good rate of growth for your trees. Annual growth is measured in late fall by measuring the distance from the tip to the enlarged area on the stem where growth stopped the previous year. Use the average of 10 terminals to establish growth. These terminals should represent different location on the tree. If growth is less than 5 inches (live oak) and there are no other stress problems, increase the fertilizer rate in late winter. However, if the growth is greater than 8 inches, reduce the rate. A starting point is to apply 0.5 lb. of ammonium sulfate (contains 24% sulfur, to aid in lowering the pH factor) per diameter inch of trunk diameter. This is the equivalent of 0.1 tenth of a pound actual nitrogen per inch of trunk diameter. The source of nitrogen can be either commercial fertilizer or from an organic source. Make the application in late February (South and South Central Texas) and early March (Central Texas and North Texas). Avoid heavy applications after mid June. (heavy applications can also create lush rapid growth which is a loud dinner bell for insects). This is especially important if a high rate of nitrogen is applied. High levels of nitrogen in mid to late summer can encourage excessive growth in early fall, that would be susceptible to sudden drops in temperature. ( Lighter and more frequent applications 3-4 times a years is more suitable to provide a consistent and more natural rate of growth for live oaks). Some trees grow at a faster rate and can safely utilize higher rates of nitrogen. Because of this it is suggested to apply fertilizer based on past year's growth and not on a set amount each year. When determining the rate always consider the past growing season and a tree's health. If a tree has been exposed to severe drought conditions or factors that caused slow growth, increasing the fertilizer rate will have little effect on recovery and can create a problem.
Nitrogen is the element most often required for growth and development. Most trees in a landscape or in nature do not need additional phosphorus or potash. There will be enough phosphorus and potash applied to the grass to satisfy the tree's needs. ( The combination of phosphorous, potassium and high alkaline soils acts as an iron and mineral blocker) . Since nitrogen is the only element applied, it can be applied to the soil surface and watered in. Do not apply any fertilizer to the surface and allow it to be exposed to high humidity or dew for extended periods of time without applying water. The nitrogen in commercial fertilizers is lost to the atmosphere when exposed to moisture for short periods of time. Also high levels of fertilizer left on grass leaves can burn. Some arborists, feel that by injecting the fertilizer, using a pressurized applicator and liquid fertilizer, the soil is benefits from the aerification.
In high alkaline soils, trees develop iron chlorosis symptoms. Some species that require well drained, acid soils. frequently develop iron chlorosis (yellowing of the leaves) when planted in alkaline soils. Sweet gum and Shumard oak are two species that frequently develop yellow leaves when grown in alkaline soils. Once established, Shumard oaks sometimes cease to develop chlorosis symptoms. Iron chlorosis is controlled with soil applications of either an iron chelate product or copperus (iron sulfate). Iron sensitive trees growing in high alkaline soils, may require a chelate. Results of field trials have shown that Sprint 138 or Sprint 330 is very effective. Also IONATETM by Hi Yield with 10% Nitrogen and 16% iron is another excellent choice for chelate iron. Be careful when using any type of iron fertilizer, they will stain walks, driveways and walls of houses.
7. Develop a landscape design that reduces foot traffic over a tree's root area. Walking or driving can cause soil compaction and result in poor root growth. Aerify the soil if compaction is suspected. Use stepping stones or mulch to form walk ways and avoid compaction. The use of mulches around the tree reduces the need for mowing.
Mowers used on turf that require frequent mowing, should be equipped with low pressure, wide tires. These spread the weight and reduce compaction. When possible do not mow when the soil is wet. Many golf courses, to prevent soil compaction, do not allow carts off the paved trails when the soil is wet or they reduce compaction by only allowing carts to drive on the trail and then go directly to the ball and then directly back to the trail after hitting the ball before proceeding along the course. Homeowners should be aware of what causes compaction and take precautions.
8. Do not dig into the root area. This results in root loss. New roots will have to be re-established at a new level. If fill soil must be applied, take precautions to insure continued water and gas exchange. After the damage has been done, it may be beneficial to install a series of small holes through the fill soil and into the normal root area. These holes will encourage water movement and gas exchange. A mix of compost and a small amount of low salt fertilizer can be used to fill the holes. The holes should be on 2-3 ft. centers and go from a few feet inside the drip line to several feet beyond the drip line. Do not use clay or slit as fill soil around trees.
9. Pruning should be restricted to dead, broken limbs or limbs that present a hazard to individuals working around the tree. Corrective pruning is sometimes needed to prevent future limb breakage due to narrow crotches. Green leaves, whatever the size are capable of manufacturing carbohydrates in the presence of sunlight. Carbohydrates provide energy for tree growth and other functions of 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.
10. In some cases, a tree may have declined to such extent that it best to remove the tree and start over with a new tree.
Proper care of tree 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 disease management program 'for trees is to prevent the problem from happening.
by Dr. Jerral Johnson
Root damage during Construction - Take precautions should be taken when planning a home or adding to the landscape to avoid practices that damage trees or their roots. Do not store sand or gravel near trees.. During construction, do not park vehicles and equipment over a tree's root system. Design landscapes to minimize soil disturbance around a tree's roots.
Mulch - If possible place mulch layer over the root system. Mulch decreases soil temperature extremes and maintains a more uniform soil moisture. It also reduces competition with weeds, grass or other plants for moisture and nutrients.
Flower beds and gardens - Avoid flower beds that must be maintained in moist condition or frequently tilled. If a flower bed is placed around a tree, protect the trunk form exposure to the organic mix by placing a collar around the base of the tree. The collar should be placed 3-4 inches away from the trunk. As the trunk expands the collar will also have to be expanded. Tilling destroys feeder roots in the top few inches of soil. Vegetable gardens should be located away from existing trees.
Poor drainage - Water is a requirement for tree growth but trapped water in the root zone can cause root mortality. During construction, internal and surface water drainage can be altered and trapped water in the root zone. In time, the oxygen is depleted and root's die. Install drains to remove excess water. if the land is sloping'. install a French drain to move the water to natural or man made drain. In some areas the land is too flat and the soil profile prevents adequate internal drainage. Drains collect and move water to a sump, and then it is removed.
Hardpan - Some soils have an impervious layer that prevents water from moving through depleted the soil profile. Oxygen is in the trapped water. if the soil below the layer will allow water to move downward, holes can be drilled through the impervious layer to improve water movement.
Water Quality - Poor quality irrigation water can create serious problems by increasing the salt content in the root zone. Roots are damaged when exposed to high salt concentrations.
Any practice that weakens or kills tree roots will encourage the invasion of fungi. These often are fungi that normally would not be a problem but because of stress, they are able to infect the roots and add to the decline.
Aerate the soil, mulch, and reduce the traffic.
Make sure you do not have heavy traffic on your tree root system. At a minimum, protect the drip line, but you really should go out further than that. If you are doing any building around a tree, put fencing around the perimeter, to protect the root system.