Resources

Developmental (Young Tree) Pruning

Developmental pruning, also known as young tree pruning, is the process of pruning young trees to develop good structure while they are still young. This type of pruning can pay dividends for generations, as one of the main ways that a tree dies prematurely is structural failure. Structural pruning practices were largely developed by Dr. Ed Gilman, emeritus professor at the University of Florida. Dr. Gilman has worked closely with Sam Hill Tree Care. He led several training sessions with our team, sharing his expertise on the intricacies of structural pruning. ## Why is Developmental Pruning Performed? Developmental pruning is performed to mimic the structure that trees develop in their natural environment. Most trees grow in forests and compete with neighboring trees for sunlight. For this reason, forest trees typically develop a single dominant trunk (called a "leader") that is tall and straight. In the absence of this competition, landscape trees are encouraged to grow horizontally rather than vertically. The resulting structure—a short, wide canopy with multiple competing leaders—is weak and prone to failure. Developmental pruning should begin as soon as possible to promote good structure. Ideally, the nursery will begin developing good structure before the tree even reaches your landscape, but unfortunately, this practice is not widespread among Texas nurseries.[^1] Developmental pruning is especially cost-effective when done in the early stages of a tree's life. Although structure can still be improved with later correction, it is more costly and rarely yields equivalent results. [^1]: Florida, home of structural pruning pioneer Dr. Ed Gilman, developed the Florida Grades and Standards for Nursery Plants in 2015. Nurseries may only sell trees graded Florida #1 or higher, so you know the tree you're getting is high quality. Unfortunately, Texas has no equivalent plant material standards, meaning nursery stock can be hit or miss. ## How is Developmental Pruning Executed? Developmental pruning involves pruning young trees every 2-3 years to develop and maintain good structure. Pruning is performed more frequently in the early life of the tree, but as it matures, the frequency can be reduced. Ideally, developmental pruning should start when the tree is planted and continue until it's about 25 years old. Your arborist will begin by examining your tree for any pre-existing structural problems and determining if corrective cuts need to be made. Next, our expert crews will make targeted pruning cuts according to those specifications. Finally, we'll continue to monitor and prune your tree regularly throughout its life. With a strong foundation established through developmental pruning, your tree will be more resilient against structural stressors like strong winds and storms.

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Emerald Ash Borer (EAB)

The emerald ash borer (EAB) is an invasive, wood-boring beetle. It was first discovered in the United States in southeastern Michigan in 2002. Experts believe the pest entered the country on solid wood packing material originating from Asia. Since its discovery, the emerald ash borer has killed millions of ash trees in North America. EAB was first confirmed in Texas on May 6, 2016, in Harrison County. It has since spread across the state, with confirmed infestations in Dallas and Denton counties. As of 2024, EAB has moved south and was recently confirmed in 5 new Texas counties. **If you have an ash tree on your property, you MUST treat for emerald ash borer every 2 years.** Otherwise, the tree should be removed and replaced with a regionally appropriate species. ## What does EAB do to ash trees? The larval stage of the borer feeds on the inner bark of ash trees, preventing the tree from transporting nutrients and water. Larvae actively feed from the early summer through the fall. Infested ash trees become stressed and decline quickly—most die within 2–3 years of initial infestation. Ash trees killed by EAB are brittle and structurally compromised, making them much more susceptible to damage caused by high winds and storms. Additionally, they are extremely dangerous to remove through conventional methods and may require costly crane removal. ## Signs and Symptoms of EAB - **Canopy dieback:** Begins in the top third of the canopy, continues until the infested tree is bare. - **Epicormic shoots:** New shoot growth proceeding from the bark of infested trees, usually found in the roots or on the trunk. The leaves from these shoots may be larger than usual. - **Bark splitting**: Vertical ruptures in the outer bark, often exposing larval feeding galleries underneath; splitting caused by host tree forming woundwood in response to larval feeding activity. - **D-shaped exit wounds:** Caused by adult beetles emerging from the bark of infested ash trees. - **Serpentine larval feeding galleries**: Found in the inner bark of infested ash trees. - **Increased woodpecker activity and damage:** Due to woodpeckers feeding on EAB larvae. ## How is EAB transmitted? Emerald ash borer, like other wood pests, may be spread when infested ash trees, logs, or firewood are moved from a quarantine zone. This may spread EAB to different regions or even between states. When the mature beetles emerge from the ash tree in June, they spread within the infested region by laying eggs inside nearby ash trees. Adult emerald ash beetles can fly at least 1/2 mile from their home tree. ## Treating EAB The most effective treatment for EAB is preventative. Treatment involves applying an insecticide to the ash tree via trunk injection. The best time to treat for EAB is in the spring while the larvae are still young and unestablished. If EAB has been detected by the presence of symptoms, the infested tree has most likely sustained significant damage. At that point, it may not be feasible to treat the infestation. Instead, the infested ash tree should be removed and destroyed in accordance with state and federal guidelines.

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Hedge Rejuvenation

Hedge rejuvenation is like a kitchen remodel for your hedges—it's a drastic, but sometimes necessary, method of overhauling old shrubs that have become overgrown and unwieldy. This process involves reducing the size of overgrown shrubs to maintain aesthetics, improve light penetration, and promote healthy growth. As with any major corrective action taken in your landscape, it's essential to have a landscape professional plan and perform these procedures. Improper pruning can cause irreparable damage to the plant. ## Why Do We Perform Hedge Rejuvenations? Hedge rejuvenations are typically performed when hedges have become unwieldy as a result of unchecked growth. The main reasons for undertaking a hedge rejuvenation are: - To reduce the size of overgrown trees and shrubs that have outgrown their space, blocking sidewalks, windows, driveways, or other features. - To improve light penetration inside the "shell" of the hedge by removing dense branches and promoting new growth. - To restore a natural form to shrubs that have been pruned into formal geometric shapes (topiary). ## How Are Hedge Rejuvenations Performed? The hedge rejuvenation process involves several key steps. First, your arborist will identify the basic limb framework of the shrub or tree. Then, we will prune out and remove excess branches to create holes and allow more light in. A moderate amount (about one-third to one-half) of old growth is removed each year for 2–3 years, with a focus on thinning density and reducing size. Due to the drastic nature of this process, hedge rejuvenations are typically performed over the course of several years in order to maintain aesthetics while promoting healthy growth. After rejuvenation, the hedges will be stronger, more appealing, and more manageable.

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Mistletoe

Mistletoe is the common name for hundreds of species of hemiparasitic plants. It sends down root-like structures, called haustoria, that penetrate through the bark into the vascular tissue of the host. Mistletoe draws nutrients and water from the host tree. Commonly infected trees include hackberry, bois d’arc, silver maple, red oak, and others. ## Is Mistletoe Cause for Concern? Mistletoe is somewhat unique because it is a hemiparasitic plant. Although they still draw nutrients and water from their host, hemiparasitic plants also perform photosynthesis and are consequently less dependent on their host for survival. Accordingly, they are less of a concern than holoparasitic plants, which survive only using resources drawn from the host. However, mistletoe can be a problem for trees that are already stressed. Trees maintain a "feedback loop" in order to achieve homeostasis. For example, in response to drought stress, a tree may close the tiny pores (called stomata) in its leaves to prevent water loss. Mistletoe, being a parasite, is not part of this feedback loop. It will continue to draw nutrients and water even while the host is trying to conserve its resources. When compounded by mistletoe, an already stressed tree may decline further. But, for the most part, mistletoe poses little threat to a healthy tree. Sam Hill Tree Care recommends removing mistletoe found on high-value trees or trees that are close to your home. For other trees, as long as the host is not otherwise stressed, consider leaving some mistletoe. Its white berries are an important food source for birds. ## Treating Mistletoe Because the haustoria penetrate into the branch, removing mistletoe is not as straightforward as pruning it out. The embedded haustoria will simply cause the mistletoe to grow back. To prune mistletoe, we remove infected branches that are 2 inches in diameter and smaller. For larger branches that should not be removed and for the trunk, mistletoe is a recurring problem that can take several years to completely eradicate. In these cases, we cut the mistletoe flush with the branch. As noted earlier, this will result in the mistletoe coming back in a few years to be pruned again. Repeatedly pruning out the new growth will offer control and gradually kill the mistletoe by starving it. Some alternate methods of controlling mistletoe have also been proposed. John Lichter and Dr. Alison Berry from UC Davis found that cutting mistletoe flush and covering the infected area with black plastic wrappings or pruning paint can control mistletoe by depriving it of light. However, this method is not always pragmatic because it is labor-intensive and the wrappings and paint may wear off. Another option is applying Florel, a growth regulator which essentially aborts the mistletoe. However, applications do not offer complete control and the spray must be carefully controlled to avoid spray drift to other landscape plants.

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Oak Wilt

Oak wilt is a fungal disease affecting oak trees. The fungus grows and spreads throughout the tree’s vascular system, depriving the host of nutrients and water. The presence of the pathogen triggers an immune response from the host tree which further blocks the movement of water. These two symptoms effectively choke the oak tree until it begins to wilt and die. ## How is Oak Wilt Transmitted? The fungus responsible for oak wilt—*Bretziella fagacearum*—is primarily spread in two ways. First, oak wilt may be transmitted over long distances by sap-feeding beetles, commonly known as picnic beetles. These beetles feed on the spore mats of diseased oak trees. The beetles then carry the spores with them to feed on the sap from a fresh tree wound, such as a pruning cut. Second, oak wilt may be transmitted by root grafting. When two trees of the same species grow in close proximity to one another, their roots will graft together and fuse, much like a skin graft. If either tree is infected, the pathogen may spread to the other. This is why oak wilt is a problem if it is present in your neighborhood. ## Preventing Oak Wilt The most important step to prevent oak wilt is to avoid wounding your oak tree when conditions are favorable for transmission. According to the Texas Forest Service, you should avoid pruning oak trees from February 1 to June 30. If it is necessary to prune or otherwise wound an oak tree in that time, a pruning sealer should immediately be applied to the wound. If oak wilt has been identified in your neighborhood, preventative oak wilt injections may protect your oak trees from the disease. The fungicide spreads throughout the vascular system of the tree, preventing the pathogen from taking root. The Texas Forest Service recommends injecting high-value oak trees that are within 75–100 ft. of a symptomatic host tree. Susceptibility to the disease varies by species. While white oaks are generally resistant to oak wilt, red oaks are very susceptible to the disease and may die within months or even weeks of infection. Live oaks lie somewhere in the middle: some die within a few months, others die in 1–2 years, and a few (about 1/10) are infected but never succumb to the disease. ## Treating Oak Wilt If your oak tree becomes infected, it is possible to perform therapeutic injections. This involves injecting the symptomatic tree with fungicide to slow and hopefully stop the development of oak wilt in that tree. The best results are achieved if no more than 30% of the canopy is showing symptoms of oak wilt. If more than 30% of the canopy is symptomatic, it is unlikely that therapeutic injections will be effective.

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