Tag leaf yellowing

Residents of North Texas are familiar with long, hot summers that take a toll on everyone and everything. From drinking extra water, keeping our pets cool, and making sure our air conditioners are working, summer in DFW can be a busy time. While watering our lawns is common practice, many homeowners do not think about the water needs of their trees. During a Texas summer, and especially when we are in drought conditions, providing adequate tree care is critical to helping your trees survive and thrive.

How Does Drought Affect Trees?

Trees are able to store water and nutrients and so may not show signs of drought stress immediately, at least not to a casual observer. When trees are greatly affected by lack of water, these symptoms are common:

• Yellowing, wilting and browning leaves
  • Leaves turning colors other than green (except in species that exhibit other colors of foliage) is often the first sign that something is wrong with a tree
• Leaf drop/defoliation
  • Keep in mind that some species (like live oaks and magnolias) exchange leaves throughout the year, rather than all in the fall, so some leaf drop is natural
• Dieback at the end of branches and limbs
  • As a tree loses vitality, the smaller growth is often the first to die
• Sunburn
  • As the canopy loses leaves, larger parts of the tree become exposed to sunlight
  • Constant exposure to light and heat causes damage to the outer layers of bark, which can start to die and fall off, exposing the nutrient-carrying parts of the tree to more heat and sun

Even when visible signs are not present, trees experience stress soon after their needs for water are not met. Some of the “invisible” signs of drought stress are:

• Death of fine, nutrient-absorbing roots
  • In addition to the large stabilizing roots, trees have fine, hair-like root structures in the top layers of soil that absorb water and nutrients
  • These roots die quickly when the soil around them becomes dry and hot
  • As these roos die, the tree loses its ability to take up moisture and nutrients from the soil, leading to further stress and dieback
• Reduced ability to fight off diseases and pests
  • If a tree is losing energy due to a lack of incoming moisture and nutrients, its defenses are less able to resist other attacks and stressors
  • If bark is being lost, pests that feed on the heartwood have easier access
• Stressors that are normally insignificant can become big issues
  • The impacts of unnecessary removal of green wood, damage to the canopy or root system, and stress from nearby activity (such as construction) are amplified by drought stress

What Can I Do to Help My Trees in a Drought?

Water. Water. Water!

The most important thing to do to help your trees is water them.

• A lawn sprinkler system is NOT enough to keep trees hydrated.
  • Trees need much more water than turf grass or smaller plants, and must be watered correctly, if there is to be any effect.
• North Texas Tree Watering Guide

Use Mulch to Regulate Soil Temperature and Moisture

Proper use of mulch around trees reduces the amount of watering needed and provides vital nutrients to the soil and tree roots underneath.

• How to Use Mulch

What to Avoid in a Drought (and Always!)

DO NOT Use High-Nitrogen Fertilizer

• Nitrogen stimulates rapid growth, which expends a tree’s depleted energy stores quickly

DO NOT Use “Weed and Feed” Products

• The “weed” component is a tree-targeting herbicide, and the “feed” is often a nitrogen-based growth stimulant

DO NOT Over Trim Trees

• Avoid unnecessary trimming and removing too much of the canopy, which reduces a tree’s ability to draw up moisture and exposes the branches to the sun

DO NOT Disturb the Area Under a Tree’s Canopy (Critical Root Zone)

• Digging, trenching, planting, construction, and other activity can destroy the fine, nutrient-absorbing roots and even damage larger roots, leading to instability

How Arborists Help in a Drought

Whether your tree is showing signs of lack of water, or is withstanding drought stress, proper tree care from an ISA Certified Arborist® is crucial to giving your trees the best chance to survive a drought.

• Proper trimming to remove dead or diseased wood, and provide airflow to keep the canopy cool
• Applying organic soil amendments designed to help drought-stressed trees supplement any lack of nutrients in the environment
• In cases of root damage, pest activity, or heat-related diseases, recommending plant health care programs designed to reduce stress and encourage healthy growth
• Reminding you to water!

Proper summer tree care (especially watering!) is the key to keeping fine root structures alive so that trees are able to get the water and nutrients they need to survive a drought. The top two to four inches of soil around the base of a tree and under the canopy is where a tree gets most of what it needs to grow. Keeping that area stable, watered, and cool goes a long way toward having trees that thrive even in a North Texas summer.

At Texas Tree Surgeons, we love trees and we love our community! The Texas drought in 2011 killed an estimated 300 million trees, including 5.6 million urban shade trees. We are keeping an eye on Texas drought conditions and adjusting our recommendations and practices accordingly. If you are concerned about your trees or have questions about how best to care for them, one of our ISA Certified Arborists® would be glad to talk to you! Contact us today!

One hallmark of summer is the dense, green foliage on broadleaf trees, but less-than-ideal circumstances can cause the rich green of healthy leaves to become pale, yellowish, and translucent. This loss of color is caused by a deficiency in chlorophyll, which is an essential part of a tree’s nutrient-gathering process. While yellowing leaves can be a sign of several different conditions, in North Texas, yellow leaves on a tree that is usually green are most often a sign of iron deficiency (“iron chlorosis”). Since the historic freeze in February 2021, we have seen a higher number of trees exhibiting iron chlorosis, as they are still recovering from freeze damage and related stress, and their ability to get essential nutrients has been compromised. Luckily, most cases of chlorosis can be remedied by soil amendments and correct, targeted fertilization.

Why Are My Tree’s Leaves Yellow?

While it is expected to see pale green or yellowish new leaves on a tree during spring, the color of these young leaves should darken as they mature. By summer, most healthy deciduous trees should exhibit rich, green leaves. (There are some species of tree with naturally red, purple, or other-colored leaves, but these are less common in North Texas.) If a tree never “greens out,” or turns green but starts to fade well before autumn, there is a systemic health issue at play. Dead or dying leaves can turn yellow, but quickly become dark grey or brown. If a tree’s leaves become pale green or yellow, and stay that way, something is preventing the tree from generating enough chlorophyll.

Chlorophyll is a naturally-occurring chemical in most plants, and performs an important function in leaves. Chlorophyll is responsible for absorbing sunlight and converting it into usable energy for the plant. Chlorophyll is adapted to absorb as much of the correct type of light as possible, and that chemical makeup causes its green appearance. While other chemicals in the leaves can appear as other colors, in most plants, chlorophyll is present in a higher concentration than other pigments, and so it is the one we most clearly see. For a majority of plants and trees, vivid green leaves are a sign of good health and proper nutrition. When leaves begin to decline and die, as in the fall, the chlorophyll fades and other colors can be seen, which is why we see a leaf color change. Similarly, health issues and stress can make plants’ leaves change colors, as the necessary chemicals become imbalanced.

What Can I Do About Chlorosis (Leaf Yellowing)?

While the underlying cause of leaf yellowing (chlorosis) is chlorophyll deficiency, that deficiency may be caused by a number of factors:

• Mineral/nutrient deficiency
• Soil acidity/alkalinity
• Poor drainage/overwatering
• Root damage/compaction
• Herbicide exposure
• Bacterial/fungal infection

Management of the cause of chlorosis is the key to bringing a tree back to health. While some factors, such as soil pH or previous chemical exposure, may not be easily remedied, drainage issues and nutrient deficiencies can often be successfully resolved. Identification of the exact cause of chlorosis can be tricky, and there may be more than one contributing factor. For a comprehensive assessment, contact an ISA Certified Arborist who can examine not only the tree itself, but the surrounding environment, and can ask the right questions to properly understand the tree’s history. Local certified arborists also have access to plant pathologists and other experts, and may be aware of a widespread issue that is affecting your tree.

A NOTE ABOUT WATERING AND FERTILIZATION

A common knee-jerk reaction to a tree or plant not doing well is to immediately increase watering and start applying fertilizer. If the chlorosis is caused by excess soil moisture, however, more watering can cause even quicker tree decline. Similarly, applying a standard, high-nitrogen fertilizer may bring temporary improvement, but can cause further chemical imbalance in a nutrient-deficient tree and stimulate quick growth that is unsustainable. It is important to understand and address the specific cause of leaf yellowing before taking action. Contact an ISA Certified Arborist for assessment and recommendations, and consider sending a sample to a plant diagnosis lab for the most accurate information.

At Texas Tree Surgeons, we love trees and we love our community! We are seeing post-freeze chlorosis on many trees in North Texas, and are working with the International Society of Arboriculture Texas Chapter as well as experts at Texas A&M University and in the tree care profession to provide the best care for freeze-stressed trees. If you have questions about your trees, freeze-related or not, don’t hesitate to get in touch!

As the summer heat drags on, we start to get calls about trees “looking bad.” Recently, for example, we have been seeing general decline of trees, especially oak trees, in the Plano area. In a densely-populated suburban area like Plano, there are many potential causes for trees showing signs of stress, displaying yellowing or browning leaves, or dropping limbs. While some issues may be symptoms of a disease, much of the oak decline we are seeing is, unfortunately, an inevitable result of the environment the trees live in.

Plano, Texas’ Urban Forest

Plano, Texas, is a great example of a community that loves its trees and values the beauty an urban forest can bring. As the city has matured, so have its trees, and many of them are now magnificent. However, when the community was planned and the trees were planted, developers depended heavily on different species of oaks: live oaks, red (Shumard) oaks, post oaks, and others. While these oaks are hardy, native Texas trees, any environment that is heavily populated by one species is susceptible to certain risks. The proliferation of oak wilt in North Texas is exacerbated by the heavy concentration of oaks in the area. Even without an outside stressor like the oak wilt fungus, any monoculture will slowly start to decline as competition for resources affects all members of a species, without the diversity necessary to replenish what was used.

The causes of oak decline in Plano run deep into the soil and deep into the history of the community. Before Collin County developed into the elegant mix of residential, commercial, and industrial areas that it is today, most of the land was used for farming and ranching. Agricultural land becomes exhausted of its nutrients after long periods of use. Moving from heavy agricultural use directly into construction doesn’t give the land time to recover. Heavy construction activity also leads to soil compaction, and if mixed fill is used, precious soil space is taken up by rocks, cement, and other inorganic material. Decades of growth and the spread of structures and concrete have further challenged the ability of Plano soils to renew themselves. Changing weather patterns in the last several years, periods of drought followed by flooding, have stressed the soil and plants even more. As turf grass has proliferated, much of the natural process that would introduce nutrients to the soil through decaying organic matter has been interrupted.

What Can I Do About Oak Decline?

While oak decline is an inevitability for many Plano oaks, the situation is not completely hopeless; there is much that tree owners can do to help restore their trees’ vitality:

• Proper Mulching
• Proper Watering
• Reducing Competition
  • Turf grass, ground cover, concrete, and over planting of trees can all contribute to nutrient competition.

However, there are some issues that may be beyond remedy:

• Poor Tree Stock
  • If the tree was sourced from a tree farm with weak stock, or with trees that had been exposed to pathogens before, it may have been at a disadvantage from the start. A plant health care program may be able to ameliorate some issues, but not all.
• Improper Planting
  • Planting issues can be corrected if the tree has not been in the ground more than a few years. The tree can possibly be re-planted, or root zone excavation can be performed to identify other root stability issues, such as girdling roots. A certified arborist can determine if any corrective efforts are possible for your particular tree.

Contacting a certified arborist to assess your trees is necessary to properly identify oak decline and address the underlying issues, not just the symptoms. Insect activity may need more involved care than just spraying a surface insecticide. Browning or yellowing leaves may be a sign of many issues: fungal root infection, insect activity, or herbicidal poisoning, and don’t simply mean that you need to water more. A certified arborist is able to evaluate the tree and its surroundings as a whole, not simply one component. An effective tree health care program involves many components: care modification, fertilization, soil management, proper trimming, pesticidal application. To preserve the value of an urban forest like Plano’s, certified arborists are key.

At Texas Tree Surgeons, we love trees, and we love our customers, in Plano and all over North Texas. If you live in Plano, and want more information about oak decline and what may be affecting your trees, let us know! If you’re not in Plano, don’t worry! We are happy to come and take a look at your trees to evaluate their health and give you the information necessary to keep them thriving for years. As always, let us know if you have any questions or concerns about trees!