Branch dieback on trees in the landscape is a concerning sight. It can happen on a newly planted tree or one that has been in the landscape for decades. Limb dieback can emerge slowly over many years. Branches develop slowly, with yellowing leaves and small or underdeveloped leaves that eventually stop emerging. Occasionally, the damage appears more quickly. Branches will leaf out in spring, and then all the leaves on a branch turn brown and fall off. Sometimes an entire branch just doesn't leaf out in the spring.
Branch dieback on trees is caused by several factors. Correctly diagnosing the problem(s) is the first step in managing an unhealthy tree. Below are some common causes of branch dieback in landscape trees. Use this guide to evaluate your tree and determine the likely cause of branch dieback.
Root Damage | Improper Planting Depth | Stem Girdling Roots | Drought Conditions | Wet Soil Conditions | Damage to the Trunk | Diseases & Insects | Winter Damage | Storm Damage | Improper Soil pH | Salt Damage | Herbicide Damage | Branch Shedding | More Information
Root Damage
Damage to the root zone from construction, compaction, or grade changes can inhibit water uptake and nutrient flow in the tree, causing branch dieback. Digging or trenching of any kind near the root zone, such as installing a new driveway or brick patio, constructing a building foundation, or installing utilities, can cause root damage. Compaction in the tree's root zone from construction equipment, the stockpiling of construction materials, or excessive foot traffic can also cause damage. Adding or removing soil in the root zone, such as to change the slope or build a retaining wall, can also cause a gradual emergence of dead branches throughout the tree's canopy.
Management Options
The only way to avoid branch dieback caused by root damage is to avoid the damage. Keep machinery that can disturb roots or compact the soil outside the tree's root zone. Once this damage has been done, the only option is to provide the best possible care for the tree and hope it can recover.
Improper Planting Depth
Planting trees with the trunk flare below the soil line may cause dieback. The trunk flare is where the trunk meets the roots and is usually indicated by a change in bark color and a flaring out or swelling at the base of the trunk. Depending on the species, problems may occur when trees are planted only a few inches too deep. Often, branch dieback from planting too deeply begins several years after planting.
Management Options
Because the problems associated with improper planting depth don't show up until several years after planting, there is nothing you can do to correct the problem. Trees are often too large and established to be practically replanted at a higher level. The only way to prevent limb dieback from planting too deeply is to place the tree at the proper depth at the time of planting.
Stem Girdling Roots
Stem girdling roots happen when a tree’s own roots either completely encircle the trunk or grow tangential to the trunk on one or more sides, causing stem compression and damaging the vascular tissue. Trees grown in smooth-walled plastic containers often develop a dense mass of roots that circle the inner wall of the pot. If these root systems are not removed or redirected at planting time, the circling roots can become problematic, stem-girdling roots. Branch dieback caused by stem girdling roots often appears 15 to 25 years after planting.
Management Options
Unfortunately, if an established tree has stem girdling roots, nothing can be done to correct it. Cutting out the offending roots will only sever a portion of the tree's root system, causing even more damage. The only way to fix stem girdling roots is to plant trees at the appropriate depth and remove or redirect circling roots at the time of planting.
Drought Conditions
When trees have a limited capacity to take up water, either because of a lack of soil moisture or a lack of roots to access sufficient water, branch dieback can be observed. Dry soil conditions are caused by drought or the lack of supplemental irrigation. Newly planted trees (those in the landscape for less than five years) and trees growing in areas with limited rooting space (such as those in parking lots or along streets) are especially sensitive to drought conditions because they have underdeveloped or limited root systems.
Management Options
Provide supplemental irrigation to young trees and those growing in locations with limited rooting areas during dry periods. Once trees have more extensive and established root systems, they will not require irrigation.
Wet Soil Conditions
Trees growing in compacted or poorly drained soils or in low-lying areas that collect water can develop a compromised root system due to the lack of oxygen in saturated soils. Water can accumulate in the rooting zone due to changes in drainage patterns, causing similar damage. Areas that were once ok but now have excess moisture may develop due to a broken irrigation head, the installation of a sump pump outlet, the redirection of a downspout, or construction or soil grade changes in an adjacent area.
Prolonged flooding or excessive irrigation can cause root damage, leading to branch dieback. Certain tree species (such as bald cypress or silver maple) will tolerate wetter soil conditions. When a tree intolerant of wet soil conditions is planted in an area that stays wet or sees periodic flooding, branch dieback is more likely to be observed.
Management Options
When soils are poorly drained, soil amendments and site grading can be made prior to planting to improve conditions. Once a tree is established, changing the soil structure or grade is not practical. On sites with wet soils, select a tree species tolerant of wet conditions. If wet conditions are caused by changes in drainage patterns or by excess water introduced into the area, adjust site conditions to direct water away from the tree's root zone.
Damage to the Trunk
Damage to the trunk from mowing equipment, string trimmers, feeding from rabbits, or antler rubbing from deer can disrupt the flow of water and nutrients in the tree and cause entire branches to die back.
Management Options
Prevention is key to avoiding limb dieback caused by trunk damage. Place physical barriers around the tree to prevent rabbits and deer from feeding or rubbing, and place mulch rings around the base of the tree to keep lawn equipment away. If damage has been done, nothing can be done to mitigate the effects. Wound dressings, pruning paints, latex paints, wrappings, and other alleged protective barriers do not help. Provide the best possible care and wait to see if the tree recovers.
Diseases and Insects
Often, insects or diseases are the first things we look to when trying to pinpoint why a tree is unhealthy. However, in many cases, environmental stress and site-related factors (abiotic issues) are the primary cause of the problem, even when insects or disease-causing agents (biotic issues) are present. Those biotic issues are more likely to become problems because the tree is weakened by abiotic factors. Several diseases and insect pests can cause branch dieback.
Vascular diseases are primarily fungi that block the flow of water and nutrients in the tree, causing entire branches to die back. Some vascular diseases, such as Verticillium wilt, affect a wide range of tree species. Many vascular diseases, such as oak wilt and pine wilt, affect only a relatively small group of closely related plants, such as those in the same genus or plant family.
Cankers are localized dead areas on the bark of stems, branches, or twigs. Most canker diseases are caused by fungi that kill the living portion of the bark. They often look like dark or sunken lesions, and the growth beyond them is damaged because canker fungi girdle the stem, preventing the movement of water and nutrients. Like vascular diseases, cankers can have a wide or narrow host range.
Foliar diseases, like anthracnose, stigmina needle cast, and rhizosphaera needle cast, can cause extensive foliage dieback and often spread branch by branch through the tree.
Root rot diseases are often caused by fungi introduced into the root system through mechanical damage or through grafts with nearby trees. They weaken or destroy the root system, limiting its ability to take up water and, as a result, leading to thinning or limb dieback.
Insect pests can also cause branch dieback in several ways. Borers, like the emerald ash borer, flatheaded borer, or peach tree borer, feed on the cambium (water and nutrient-conducting tissue) just below the bark. This feeding causes girdling that can result in limb dieback. Other insects, like scale and aphids, tend to cluster on branches, causing the branch to decline in health.
Management Options
Accurate identification of the disease or pest causing the dieback is the first step to managing the problem. For certain diseases or insect pests, pesticide applications may be effective in preventing further damage. Other diseases or insects, such as cankers and scale, may be effectively pruned out to prevent their spread to other branches. Many trees are too large to be treated effectively with a fungicide or insecticide, and the only course of action is to provide the best possible care and see how the tree responds. In some situations, the tree will tolerate or recover from the damage; in others, the tree will be lost.
The Plant and Insect Diagnostic Clinic can help identify disease and insect issues.
Winter Damage
Branch dieback from winter damage can be caused by both low temperatures and desiccation.
Extremely low winter temperatures can cause branches to die back, especially on species that are marginally winter-hardy in Iowa. Sometimes this damage shows up as entire branches that don't leaf out in spring. Other times, trees may have a flush of leaves in spring, which then turn brown later in the growing season.
Dieback can also be observed in evergreen trees due to dry winter conditions. On sunny, windy days during the winter when temperatures are above freezing, leaves and needles lose (transpire) water. If the soil is frozen, transpired water cannot be replenished, causing the tree to suffer from desiccation stress. Often, this damage is observed on branches located on the windward side of the tree.
Management Options
Any dead branches can be pruned out. When damage is minimal, the tree can continue to grow and fill in the gaps created by the lost limbs. For young trees that lose their central leader, a new branch will need to be trained to become the central leader. If what remains after removing winter-damaged limbs is not acceptable, the tree will need to be removed and replaced.
Storm Damage
Often, when storms damage trees, they completely sever limbs from the tree. However, wind, snow, and ice can partially break limbs, and the damage may not be apparent, especially on branches high in the tree canopy. Partially broken branches have a reduced ability to transport water and nutrients, which causes leaves on the branch beyond the damage to wilt or die.
Management Options
Any damaged branches should be pruned out. Cleaning up ragged edges and making a new pruning cut at the base of the branch will allow the tree to recover more readily from the damage. When damage is minimal, the tree can continue to grow and fill in the gaps created by lost limbs. For young trees that lose their central leader, a new branch will need to be trained to become the central leader. If what remains after removing broken or damaged branches is not acceptable, the tree will need to be removed and replaced.
Improper Soil pH
Most trees grow best in soils with a pH between 6.0 and 6.5. Most Iowa soils have a pH between 5.5 and 7.5, a range most trees tolerate well. But pH can range from 4.5 to 8.2. When soil pH is much higher or lower than preferred by the tree species, it can cause problems such as leaf chlorosis (yellowing) and limb dieback. Some tree species tolerate soil pH extremes more readily than others. Branch dieback is more common in species that are more intolerant of excessively high or low soil pH (such as pin oak at high soil pH).
Management Options
The best way to address this issue is to plant a tree that is better suited to the soil in your landscape. For established trees, you can treat them to mask symptoms (e.g., with an iron chelate), or you can adjust the soil pH in the root zone. Soil pH can be adjusted, but it is not always easy, especially around established trees. After a soil test determines the pH, use elemental sulfur or lime to lower or raise the pH in the tree's root zone.
Salt Damage
Deicing salts can damage trees when used in excess. The damage is most severe near major streets and highways, where salt from runoff accumulates in the soil. Salt-laden spray from passing vehicles can also damage roadside plants, particularly evergreens.
Salts affect plant growth in several ways. When soil contains high salt levels, plants cannot absorb sufficient water even when soil moisture is plentiful. Plants suffer a salt-induced water shortage. High salt levels restrict the uptake of essential nutrients by plant roots. Salt deposited directly on plant foliage from road spray can cause plant tissue dehydration. These problems can occur across the entire tree or be localized to one side or several branches, especially those closest to the source of salt.
Management Options
Use deicing salts sparingly to avoid accumulation in the soil. Barriers like burlap can prevent salt-laden road spray from getting on branches or leaves. As soon as the ground thaws in early spring, water heavily salt-affected areas where salt has accumulated over winter. A thorough soaking should help flush the salt from the root zone of plants. When planting trees near major streets or highways, select salt-tolerant tree species.
Herbicide Damage
Herbicide damage can manifest in a wide range of symptoms, including leaf cupping, petiole twisting, epinasty, blotches, color changes, severe tissue distortion/deformation (especially on new growth), low vigor, and/or plant death. Herbicide injury typically affects all or most plants in an area, regardless of species, although some species may be more sensitive and therefore more likely to develop symptoms. Herbicides typically cause an overall decline in tree health, but depending on the herbicide source, active ingredient, and application method, the effect can be confined to a single branch or the side of the plant closest to the source of drift.
Management Options
Trees damaged by herbicide may or may not recover, depending on the severity of the damage. All that can be done is to wait and see what happens while providing good care for the plant. When herbicide injury is observed, no chemical sprays or nutrient/fertilizer applications can reverse the damage. Often, new growth is unaffected, and long-term damage may not occur. This depends on the plant species, its overall health, and the product to which it was exposed.
Branch Shedding
Branches are shed from trees when they no longer serve a purpose. As trees get larger, upper limbs can cast more shade on lower limbs. Trees can also cast shade on nearby trees. When light levels become low enough, the tree will shed this lower or interior branch. This is a natural process for trees and often happens gradually over many years.
Management Options
No management is needed, as branch shedding is normal and does not damage the tree. Dead limbs can be pruned out to improve safety and appearance.
More Information
- Identifying Tree Problems (publication)
- Understanding Decline in Trees (publication)
- How to Diagnose Problems with Trees in the Landscape
- Browning and Dieback on Conifers
- Decline of Newly Planted Trees
- Understanding the Effects of Flooding on Trees (publication)
- Managing Storm-Damaged Trees (publication)
- Common Problems of Ash Trees (publication)
- Care of Newly-Planted Trees
- How to Remove Tree Stumps
- Community Tree Planting and Care Guide (publication)
- Choosing an Arborist (publication)