Tag fungal infection

Why Is My Tree Turning Yellow?

by Texas Tree Surgeons Ask Texas Tree Surgeons, Resources, Tree Health Care

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!

Ask Texas Tree Surgeons: What’s Wrong With My Oak Trees?

by Texas Tree Surgeons Ask Texas Tree Surgeons, Tree Health Care

Another installment in our series of posts where Texas Tree Surgeons answers your tree questions. Are you having problems with your trees and want to know what’s wrong? Let us know!

The leaves on our oak trees are looking diseased, with bumps all over them. Is this oak wilt?

Oaks are the most common trees in our North Texas urban forest, and they can suffer from many different health issues. If your oak is showing misshapen leaves with bright green bulges on them, it is most likely a fungal disease that may look bad, but is not usually harmful to the overall health of the tree.

Oak Leaf Blister 

  • Oak leaf blister is caused by the fungus Taphrina caerulescens, which enters the new leaf buds during cool and moist spring weather.
  • The fungus causes the young leaves to develop blister-like bumps on their surfaces, with coloration ranging from light green to brown.
    • In more severe cases, the leaves may fall off altogether.
    • The fungus does not affect mature leaves, only new growth.
  • Like other fungal diseases, oak leaf blister is more prevalent during periods of cooler weather with increased rainfall in the spring, and cannot survive the summer heat.

Does Oak Leaf Blister Kill the Tree?

Oak leaf blister and the T. caerulescens fungus do not pose a serious risk to the health of affected trees.

Can Oak Leaf Blister Be Treated?

  • The spores which carry the oak leaf blister fungus are present on the bud sites over the winter, and once the tree begins showing infected leaves, chemical treatment is not effective.
    • It is possible to apply a preventative fungicide, but this must be done before bud break and while the young leaves are maturing.
  • If you have a tree with oak leaf blister, the best course of action is to clean up fallen infected leaves and dispose of them in plastic bags.
    • Do not place leaves in compost, as this may encourage further fungal growth.
  • Keeping a tree healthy with proper mulching and fertilization, as well as maintaining soil drainage, will help it resist future health issues.

At Texas Tree Surgeons, we love trees and we love our customers! While oak leaf blister can be unsightly, it is mostly harmless and is not a serious concern to the health of the tree. Of course, there are many oak health issues that can cause long-term damage and tree death. Oak wilt is a major concern. Trimming oaks should be avoided between February and July if possible, and proper precautions taken if trimming cannot be postponed. Oak decline is also a problem, especially in areas where many of the trees were planted around the same time, and are reaching the end of their lifespan. If you have any questions about the health of your oaks, or any other tree care issues, let us know!

Ask Texas Tree Surgeons: My Tree is Leaning; Should I Be Worried?

by Texas Tree Surgeons Ask Texas Tree Surgeons, Tree Health Care

Another installment in our series of posts where Texas Tree Surgeons answers your tree questions. Are you having problems with your trees and want to know what’s wrong? Let us know!

We have a tree in the back yard that is leaning. Is there anything we can do to fix it?

Whether you just moved into a new house and noticed one of the trees is leaning, or a tree has suddenly developed a lean, there is one important difference to be aware of: quickly-developed leans and over-time leans.

Leaning Trees: Fast vs. Slow

 The main factor that determines whether a tree that leans is a problem or not is how quickly the lean developed:

  • Trees that have developed a lean over time usually are not a high risk, and cannot be straightened or corrected.
    • Trees, like other plants, are naturally drawn to the sun and away from other trees and structures. (This phenomenon is called “phototropism.”)
    • If a tree faces competition for sunlight, it will begin to lean away from its competitors and towards a clear view of the sun.
      • As the tree leans, its roots grow out in the opposite direction from the lean to anchor the tree.
    • Once the tree has become established with its lean, it will continue to grow that way.
      • In some cases, a tree that was leaning can begin to send new growth vertically upward again, once the competition for sunlight is removed, but the leaning parts will remain.
  • Trees that develop a lean quickly can be an increased fall risk.
    • Whether the tree is large or small, developing a lean quickly usually means one thing: root system instability.
      • A tell-tale sign of a root issue causing a lean is raised ground around the tree or disturbance to nearby structures or fences.
    • High-limestone and shallow soils, like we have in much of North Texas, can be a contributing factor to shallow roots which can lead to instability.
      • Additionally, periods of drought and flooding cause shifts in the soil, further hampering proper root formation.
    • Root rot, often caused by fungus, can cause widespread root system death, leading to major structural instability.
    • If there has been construction around the tree and roots have been cut, or the tree suffered storm damage, a lean can be a sign of an imminent fall.

What Can I do About a Leaning Tree?

 If the tree has grown into a lean over time, there is little that can be done. Once the tree is established and stable in its leaning orientation, trying to straighten it can destabilize the structure and put the tree at risk of falling.

For a sudden lean, however, it is important to act quickly. Whatever the cause of the lean, it must be addressed before it becomes worse and the tree falls. In some small trees, a sudden lean can be corrected, allowing the tree to grow new stabilizing roots. In large trees however, complete removal is often the only safe way to deal with a sudden lean. If the tree is leaning from storm or other damage, especially when roots have been cut, rope off the area under the tree and contact a certified arborist immediately — the tree could fall at any time.

 At Texas Tree Surgeons, we love trees and we love our customers! If you notice that one of your trees in leaning, we are always happy to come out an see what may be causing the lean and whether it needs to be addressed. If you are aware of a tree that has developed a sudden lean, contact us today so that one of our ISA Tree Risk Assessment Qualified arborists can properly evaluate the danger of the situation and provide a solution.

Ask Texas Tree Surgeons: Why Do My Red Tip Photinias Have Spots on the Leaves?

by Texas Tree Surgeons Ask Texas Tree Surgeons, Tree Health Care

Another installment in our series of posts where Texas Tree Surgeons answers your tree questions. Are you having problems with your trees and want to know what’s wrong? Let us know!

Dear Texas Tree Surgeons,

A lot of my bushes, especially the red tip photinias, are starting to wilt and have reddish-brown spots on their leaves. What can I do about that?

Red Tip Photinias have long been a staple of North Texas flowerbeds and hedgerows. Hardy and fast-growing, the evergreen shrub can be trimmed to various heights and forms a good privacy barrier with its broad leaves. New growth has red leaves, giving the red tip photinia its name. Unfortunately, red tip photinias are particularly susceptible to leaf spot diseases.

This fungus Entomosporium mespili causes leaf spot on all members of the rose family, including red tip photinias. Starting as a red, brown, or black dot on leaves, the leaf spot expands outward as the fungus grows. Eventually, the red spots turn into a gray area rimmed by red. As the fungus spreads, it disrupts vascular function in the leaves, which eventually fall. The fallen leaves collect moisture at the base of the shrub, increasing fungal growth. As wet conditions continue, the fungus can spread its spores within water droplets, such as splashing from rain or irrigation. Left unaddressed, the fungus will spread throughout the photinias, causing wilting and dieback.

Environmental control

The first line of defense against fungal leaf spot, as with many fungal diseases, is to monitor watering and drainage. Fungi thrive in wet conditions of a moderate temperature, so the spring and fall are when we see the most activity. In periods of wet weather, the clay soil common to much of North Texas can hamper proper drainage, causing the area around the red tip photinias to become waterlogged. This moisture, mixed with the fallen and decaying organic material creates the ideal conditions for fungal growth. Even if the soil drainage cannot be improved, it is important to curtail watering so as not to make the situation worse.

In addition to moisture, the fallen photinia leaves contribute to the growth of the Entomosporium fungus. Keeping the area around the plants clear of debris can help slow fungal progression. In a similar way, dense foliar growth on the interior of the red tip photinias can collect moisture. Where possible, thin out dense areas to allow light and air to circulate. When trimming, make sure to remove any areas already showing leaf spot. Removed material, especially infected leaves, should be buried or disposed of in a plastic bag.

Chemical Control

Fungicides can be used to control Entomosporium leaf spot, but the process can be costly. Furthermore, treatment will be ultimately ineffective if the environmental factors are not eliminated. For valuable hedges, a continuous process of multiple-week treatments in the spring and fall may be recommended. In other situations, it can often be more cost-effective and better in the long-term to remove the affected plants and replace with a less-susceptible species. 

While there is no quick solution for red tip photinia leaf spot, we hope this information can help homeowners mitigate the damage to their shrubs, and decide if treatment or removal might be warranted. At Texas Tree Surgeons, we love trees (and shrubs! and hedges!) and we love our customers, and we always want to give our community the best, most accurate information regarding their plants. If you would like one of our arborists to come out and see how your photinias, or anything else, are doing, let us know!

What is Oak Wilt?

by Texas Tree Surgeons Resources, Tree Health Care

What is Oak Wilt?

At Texas Tree Surgeons, we love trees and we love our customers, and we have created a series of articles covering tree basics. If you have a specific tree question, let us know!

Oak wilt, and the precautions that need to be taken to help prevent the spread of this fungal disease, may be the most often talked-about aspect of tree health care in Texas. Throughout the state, tree owners and communities are challenged by the potential devastation to all species of oak tree. In some areas, there are ordinances in place that restrict oak trimming in order to prevent the spread of the disease. Other areas have no formal regulation, and this can lead to a lack of awareness and a potential for widespread infection.

While oak wilt is a serious threat to our North Texas urban forest, there are simple steps that everyone can take to lessen its impact.

What kind of Disease is oak wilt?

Oak wilt is an infectious disease caused by a fungus (Bretziella fagacearum*). All oaks (genus Quercus) are susceptible to oak wilt, but different species may react differently to the fungus. Oak wilt is a vascular disease, and infects the whole tree, even if only one part is symptomatic. As the fungus spread through the tree, it blocks the transmission of nutrients to the canopy, causing the characteristic “wilt,” or dieback.

In live oaks, infected leaves often show yellow-brown veins, even while still on the tree. In red oaks, leaves may simply wilt and brown. This process can lead to an autumn-like coloration during the summer. Additionally, fungal mats may form underneath the bark of red oaks, leading to cracking, peeling bark and a rotting smell.

While visual inspection is a strong indicator of the presence of the oak wilt fungus, laboratory confirmation may be required. The Texas Plant Disease Diagnostic Laboratory offers testing for oak wilt and many other diseases. For more information on how to submit a sample, see this post or contact your arborist.

Live oak leaves showing the venal necrosis characteristic of oak wilt

How do trees get oak wilt?

The most common ways for the oak wilt fungus to be transmitted are by insect activity and root grafting. Insects can infect a tree through any exposed wood (not covered by bark) or open wound (such as a pruning cut, broken limb, or where branches rub against each other). In situations with oaks planted in close proximity, the fungus can be transmitted from one tree to another via underground root grafting. As roots make contact with other roots, they grow together and share pathogens.

Different species of oak can contract and spread oak wilt by different methods.

RED OAKS

Red oaks (Texas, Shumard, blackjack, water) are extremely susceptible to infection through insect activity. Red oaks are often the primary mode by which oak wilt gains a foothold in a new area. The oak wilt fungus thrives in red oaks and creates visible fungal mats underneath the bark. These spore mats attract insects; sap beetles of the Nitidulidae family are the most common type. Beetles feed in the infected area and become covered with particles from the spore mats. Drawn to exposed wood on healthy trees, the beetles transfer the fungal spores, spreading the infection.

LIVE OAKS

In contrast to red oaks, live oaks are susceptible to oak wilt primarily through their root systems. In nature, live oaks often grow in groups, sometimes called motts. Underneath the mott, the root systems of the individual trees become interconnected. This grafting allows not only nutrients to be shared, but pathogens as well. Once a member of the mott has contracted the oak wilt fungus, the infection quickly spreads.

WHITE OAKS

White oaks (post, bur, chinkapin) are more resistant to oak wilt than other species, but are still at risk. Transmission generally occurs through spore transfer by insects, or by human activity.

Can you prevent Oak Wilt?

Oak wilt is an epidemic. Because of the concentration and susceptibility of oaks in Texas, especially red oaks, it can be difficult to isolate centers of infection and prevent further spread. The Texas A&M Forest Service and the Forest Health Protection branch of the U.S. Department of Agriculture have issued some guidelines to help prevent further tree death.

  • Remove and properly dispose of diseased red oaks immediately
    • Chip or bury all tree material
  • Do not transport unseasoned firewood
    • Firewood should be dry, splitting, and the bark should be peeling off
  • Do not store unseasoned oak firewood uncovered
    • Cover tightly with heavy, clear plastic and bury the edges to restrict insect access
  • Do not prune or otherwise wound oak trees from February 1 to July 1
    • The best time to trim is in the fall and winter
  • When infection is a risk, take proper precautions
    • Sterilize tools and paint cuts

If you have healthy oak trees in an area with infected trees, preventative treatment may be effective in slowing transmission. As oak wilt is a systemic, vascular disease, the most effective treatments consist of injecting the infected trees with a fungicidal chemical. The only currently recommended fungicide is Alamo®, a formulation of the fungicide propiconazole. The fungicide is administered through holes drilled in the root flare of the infected tree and should only be applied by Texas Department of Agriculture Licensed Applicators.

For large stands of oak trees, especially live oaks, trenching around the area and severing root connections can limit disease spread, as well.

A typical system for fungicidal injection; each green port is inserted into the living tissue of the tree.

Can you cure Oak Wilt?

There is no known cure for oak wilt. Reported home remedies or substances applied to the exterior of the tree have not be proven to have any remedial effect. If you have a tree that is infected with oak wilt, be sure to consult a Texas Oak Wilt Qualified arborist or your local Texas A&M Agrilife Extension agent to discuss treatment options.

Red oaks usually defoliate and die one to six months after becoming symptomatic. Live oaks may last up to a few years before total necrosis. White oaks show the most resistance to oak wilt and may survive several years after infection.

Fungicidal treatment may prolong the life of infected trees, but cannot eradicate the disease. However, systemic fungicides are most effective if a tree has not lost more than 30% of the crown. Contact a certified arborist to see if your tree may be a good candidate for treatment.

What areas have Oak Wilt?

In North Texas, there are many centers of infection. At Texas Tree Surgeons, we take oak wilt precautions throughout our service area. Still, there are a few neighborhoods in which we have seen particularly bad oak wilt activity:

  • Preston Hollow, Dallas
  • Lakewood, Dallas
  • Walnut Hill and Abrams, Dallas
  • Coit and Campbell, Richardson
  • President George Bush Turnpike and the Tollway, North Dallas
  • Park and US 75 in Plano
  • Highland Park
  • University Park

If you live in one of these areas, or suspect oak wilt activity in your neighborhood, contact your arborist to see what specific preventative steps are recommended for your trees.

Oak wilt is one of the greatest threats to trees in Texas. Education, awareness, and prevention are the best tools we have to protect our urban forest from devastation. If you want to learn more about oak wilt, visit TexasOakWilt.org.

At Texas Tree Surgeons, we love trees and we love our customers, and we believe that the more people learn about their trees, the better we can serve our community. We have several Oak Wilt Qualified arborists on staff; please let us know if you have any questions about oak wilt or any other tree question. We are always happy to help!

* – Until 2017, the oak wilt fungus was identified as Ceratocystis fagacearum.