Cotton root rot (CRR) is soilborne fungal disease that attacks the roots of susceptible plants. Without functioning roots, the host cannot take up water, resulting in rapid decline and death. It is also called “Texas root rot” because of its prevalence in Texas, although it is common throughout the southwestern United States. The disease is called cotton root rot because it is frequently found on cotton. Cotton is a woody plant that is closely related to trees and shrubs. As a consequence, CRR has a very wide host range, affecting more than 2000 plants. Members of the _Rosacae_ family, such as Bradford pears and photinias, are especially susceptible. ## The Disease Triangle and Cotton Root Rot One of the fundamental models we use in plant science is the disease triangle. It illustrates the interaction between the three factors necessary for disease: a susceptible host, the presence of a pathogen, and favorable environmental conditions. When these three elements converge, disease can occur. Like with [take-all root rot (TARR)](https://samhilltreecare.com/resources/take-all-root-rot), understanding the disease triangle can help us better understand and combat cotton root rot. ### Susceptible Host As mentioned earlier, cotton root rot has a very wide range of hosts—more than 2000 different plants. Members of the _Rosacae_ family are especially susceptible. ### Presence of the Pathogen Cotton root rot is very common in North Texas soils. The fungal pathogen responsible for CRR, _Phymatotrichum omnivorum,_ makes ball-like reproductive structures (called sclerotia) known to persist in the soil for up to 50 years. Because large swaths of our land were once used for cotton farming, the soil in even many residential areas still contain the sclerotia from past CRR infections. ### Favorable Environment Cotton root rot flourishes in high temperatures, alkaline conditions, and excess moisture. Unfortunately, these exact conditions are found all over Dallas. Our soils are clay-heavy and drain poorly. They are also calcareous (high in calcium), making them relatively alkaline (pH 7.8–8.2 on average). ## Signs of Cotton Root Rot Because it kills the host so quickly, diagnosing CRR is often a post-mortem. The diagnostic symptom is cinnamon colored strands (called rhizomorphs) on the roots of the host. These strands are needlepoint-like and crossed. During warm, rainy weather, the pathogen may form spore mats on the soil surface, like those depicted in the picture above. ## Treating Cotton Root Rot Unfortunately, little can be done to treat cotton root rot aside from amending the soil to lower the pH. If the host has died and must be removed, be sure to replant with a more resistant species. Some experimental fungicides have shown promise and may prove useful in the future, but they are not available commercially as of yet.

Dutch elm disease is a serious fungal disease affecting elm trees. The disease was first introduced to North America in 1928 on imported timber. It is principally caused by two related fungi, _Ophiostoma ulmi_ and _Ophiostoma novo-ulmi._ Dutch elm disease typically spreads in one of two ways: 1. Elm bark beetles may carry the fungal spores between susceptible hosts at some distance. 2. Neighboring elm trees may form root grafts through which the fungus may spread. The introduction of Dutch elm disease led to a massive epidemic in the elm trees of North America. The disease killed off a huge swath of American elm trees in the mid-twentieth century. Americans elms (_Ulmus americana_) were once a nearly ubiquitous species. Favored for their ability to form a neat, closed canopy, the American elm was a popular choice for planting along city streets. They are now a rarity in many parts of the country they once dominated. ## Dutch Elm Disease in Texas Dutch elm disease is an ongoing problem in the Northeastern and Midwestern United States. It is comparatively less common in Texas. Some speculate that Dutch elm disease may be less common here because the pathogen is sensitive to heat. This theory aligns with our experience—we see infections flare up most when temperatures are mild. Dutch elm disease is also gaining a foothold in some pockets of north Texas. In particular, most infections are concentrated in the Mid-Cities region; there have been confirmed infections in Murphy, Sachse, Flower Mound, and Grapevine. ## Symptoms of Dutch Elm Disease Similar to oak wilt, the fungal spores spread throughout the vascular system of the tree. In an attempt to stop the spreading pathogen, the tree plugs the water-carrying vessels with balloon-like structures called tyloses. Unfortunately, this immune response does not occur quickly enough in susceptible species. The response is actually counter-productive. Rather than containing the fungi, the tree loses its ability to transport water up the trunk. In Texas, the symptoms of Dutch elm disease are most visible when temperatures begin to rise—from mid-May to early June. The leaves on the outer crown wilt and turn yellow. Eventually they turn brown and may be shed from the tree. As the infection progresses, the yellowing and wilting advances along the infected branches from the outer crown down toward the trunk. Another symptom of Dutch elm disease is brown streaks running lengthwise along the sapwood of wilted branches. This symptom is often missed because the bark must be removed in order to observe it. Properly diagnosing Dutch elm disease can be tricky. In our climate, heat and water stress are common concerns. For this reason, Dutch elm disease may be mistaken for a lack of sufficient water. Positive diagnosis typically involves sending a branch sample to a plant diagnostic clinic. ## Treating Dutch Elm Disease Preventative treatments are the most effective way to lower the risk of Dutch elm disease. If you live in a pocket of infections, such as the Mid-Cities, it's important to monitor your landscape and neighborhood for signs of Dutch elm disease. If the disease is a recurring problem in your area, consider preventative treatments every 1–3 years. When branches start flagging due to wilt, we can begin "bark tracing" to remove infected tissue and, hopefully, contain the spread of the disease. Root grafts should also be broken by trenching in order to prevent the disease from spreading to neighboring elm trees. If symptoms have progressed and management is no longer possible, the infected tree should be removed and properly disposed of. ## Additional Resources The University of Minnesota Extension has a [great general factsheet](https://extension.umn.edu/plant-diseases/dutch-elm-disease) on Dutch elm disease. Minneapolis–Saint Paul still has a vibrant population of American elms in what would otherwise be a hotbed of infections. This is largely due to their excellent management strategies at the community level. David N. Appel, Professor Emeritus in the Department of Plant Pathology & Microbiology at Texas A&M, wrote an excellent [primer on Dutch elm disease in Texas](https://www.texasinvasives.org/resources/publications/DUTCH_ELM_DISEASE_Appel.pdf) some years ago. He discusses the nuances of the disease in Texas specifically.

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.

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 infested trees include hackberry, bois d’arc, cedar elm, 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 infested 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 infested 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.

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.

Take-all root rot (TARR) is a fungal disease affecting most warm-season grass species, such as Bermuda, Zoysia, and St. Augustine grasses. The disease is called "take-all" root rot because if left unchecked, it "takes all" the grass by killing the root, leaving patches of bare soil. It is caused by the fungus _Gaeumannomyces graminis_ var. _graminis_. Take-all root rot prevents the grass roots from taking up water and nutrients from the soil. The first sign of TARR is grass that looks yellow and sickly. As it progresses, it causes severe dysfunction of the roots. The affected turfgrass will start dying in patches. Diagnosis by an expert is usually possible without laboratory testing. The fungus is most prevalent when soil temperatures are within its ideal range (55–85 °F.). Our soil temperatures typically fall within this range for two periods each year: 1. March–April: when grass begins to emerge from winter dormancy. 2. September–November: when temperatures have fallen from their summer highs. TARR also favors alkaline (high pH) soils which are prevalent in Dallas.[^1] We see infestations most frequently on established lawns. Sodded lawns carry soil from the nursery, which is normally treated with fungicide to prevent TARR. [^1]: Dallas soil is about 7.8 to 8.2 pH on average. ## Preventing Take-All Root Rot Preventing TARR can be challenging. The pathogen is very widespread. In a 1999 survey of Dallas lawns, Dr. Phil Colbaugh found the TARR pathogen in 61% of lawns surveyed.[^2] Furthermore, most turf grasses used in our area are susceptible to the disease. As such, prevention efforts focus on improving overall turf health. To improve overall turf health, two important factors to address are watering and mowing. [^2]: https://gregg.agrilife.org/files/2011/09/takeallpatchresearch_12.pdf ### Watering Watering appropriately and ensuring proper drainage is an important part of keeping your turf healthy. Our local soils are clay-heavy and drain very slowly. Construction, vehicles, and other human activities worsen water flow by compacting the soil. Combined with natural topography, your landscape likely has some areas with poor drainage. ### Mowing Another important element of turf health is mowing height. Mowing too short can make TARR more severe. You should also mow frequently enough to avoid removing more than one-third of the leaf height at once. Additionally, turf in shaded areas of your landscape should be left taller than turf in sunny areas. The leaf blade is like a solar panel; shaded turf needs more surface area. Unsure how high you should be mowing? [This guide](https://aggieturf.tamu.edu/wp-content/uploads/sites/24/ESC052-1.pdf) from the Texas A&M AgriLife Extension is a great primer. ## Treating Take-All Root Rot Treating take-all root rot takes a multi-faceted approach. First, we stop any cultural practices that could inhibit treatment.[^3] After diagnosis, we usually begin treatment with fungicide applications. The applications give us a foothold to improve environmental conditions and make the soil unsuitable for the TARR pathogen. The TARR pathogen does best in alkaline soils, so using soil amendments to lower the pH is another treatment option. We do this by adding peat moss or an acidifying fertilizer to the soil. However, any pH treatment will eventually be counteracted over time by our alkaline water supply. Once a site has been infested, preventative fungicide injections should be made in following years during the windows when TARR is active. [^3]: For example, certain herbicides can contribute to the severity of the disease. Some pre-emergent weed killers work by temporarily pruning the grass roots. Since TARR also afflicts the roots, the compound effects of TARR and herbicides can kill a lot of grass quickly.