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 slow growth, 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 a number of factors. Correctly diagnosing the problem(s) is the first step in managing an unhealthy tree. Below are some common causes of branch dieback on trees in the landscape. 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
Damage to the root zone due to construction, compaction, or grade changes can inhibit the uptake of water and flow of nutrients 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 to do something like change the slope or build a retaining wall can also bring about a slow emergence of dead branches throughout the canopy of the tree.
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 care possible for the tree and hope the tree can recover.
Planting trees with the trunk flare below the soil line may cause dieback in trees. 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 the tree.
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 practically replant the tree 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 planting time.
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, then those circling roots can become problematic stem girdling roots. Branch dieback caused by stem girdling roots often shows up 15 to 25 years after planting.
Unfortunately, if an established tree has stem girdling roots, nothing can be done to correct it. Cutting the offending roots out will only cut the tree off from a portion of its root system, causing even more damage. The only way to fix the issue of stem girdling roots is to plant trees at the appropriate depth and remove or redirect circling roots at the time of planting.
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 a limited rooting area (such as those in parking lots or along streets) are especially sensitive to drought conditions because they have under-developed or limited root systems.
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.
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 because of a change in water drainage patterns causing similar damage. Areas that were once ok but now have excess moisture may develop because of a broken irrigation head, the installation of a sump pump outlet, the redirection of a downspout, as well as 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.
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. In sites with wet soils, select a tree species that is tolerant of wet conditions. If wet conditions are caused by a change in drainage patterns or excess water being introduced to the area, change the site conditions to direct water away from the tree's root zone.
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.
Prevention is key to avoiding limb dieback caused by damage to the trunk. Place physical barriers around the tree to prevent feeding or rubbing by rabbits and deer, 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 care possible and wait to see if the tree will recover.
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 issues with the site (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 an issue because the tree is weakened by abiotic issues. 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, like Verticillium wilt, impact a wide variety of tree species. Many vascular diseases, like oak wilt or pine wilt, only impact 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 and prevent the movement of water and nutrients. Like vascular diseases, cankers can have a wide or narrow host range.
Root rot diseases are often fungi introduced to the root system by mechanical damage or grafts with nearby trees. They weaken or destroy the root system limiting its ability to take up water, and as a result, thinning or limb dieback is observed.
Insect pests can also cause branch dieback in a number of ways. Borers, like 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 together on branches causing that branch to decline in health.
Accurate identification of the disease or pest causing the dieback is the first step to managing the problem. For some diseases or insects, pesticide applications may be possible to prevent 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 practically be treated with a fungicide or insecticide and the only course of action is to provide the best care possible 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.
Branch dieback from winter damage can be caused by both low temperatures and desiccation.
Extreme low temperatures in winter 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 emerge in spring and then turn brown later in the growing season.
Dieback can also be observed for evergreen trees because of 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, the transpired water cannot be replaced and the tree suffers desiccation stress. Often this damage is observed on branches located on the windward side of the tree.
Any branch that is dead 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 a central leader. If what is left behind after removing winter-damaged limbs is not acceptable, the tree will need to be removed and replaced.
Often when storms cause damage to trees they completely sever the limb 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.
Any branch that is damaged 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 a central leader. If what is left behind after removing broken or damaged branches is not acceptable, the tree will need to be removed and replaced.
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 be as low as 4.5 or greater than 8.2. When the soil pH becomes much higher or lower than what is preferred by the tree species, it can cause problems like chlorosis (yellowing) of the leaves and limb dieback. Some tree species tolerate extremes in soil pH more readily than others. Branch dieback is more common on species more intolerant of excessively high or low soil pH conditions (such as high soil pH with pin oak).
The best way to deal with this issue is to plant a tree that is more suitable for the soil in your landscape. For those trees already established, they can be treated to mask the symptoms (such as with an iron chelate), or you can work to change 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 is conducted to determine the pH, utilize elemental sulfur or lime to lower or raise the pH in the tree's root zone.
Deicing salts can damage trees when used in excess. The damage is most serious near major streets and highways where salt from run-off 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 high salt levels are present in the soil, plants cannot absorb sufficient water even though soil moisture is plentiful. Plants suffer a salt-induced water shortage. High levels of salt restrict the uptake of essential nutrients by plant roots. Salt deposited directly on plant foliage from road spray can cause dehydration of plant tissue. 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.
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, heavily water areas where salt accumulates 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 has a wide range of symptoms including leaf cupping, petiole twisting, epinasty, blotches, change of color, 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 can be more sensitive than others 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, it could be isolated to one branch or side of the plant closest to the source of drift.
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 it was exposed to.
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 other trees growing nearby. 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.
No management is needed as branch shedding is normal and does not cause damage to the tree. Dead limbs can be pruned out to improve safety and appearance.
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- 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
- Community Tree Planting and Care Guide (publication)
- Choosing an Arborist (publication)