How to Check a Tree for Root Rot: Signs, Digging and Lab Samples

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How to check tree for root rot starts with the symptoms above ground, then look at the roots themselves, and send samples to a diagnostic lab when the signs point to a root disease. Purdue University’s plant pathology guide and the University of Maryland Extension page on root rots both say root problems are easy to miss, because the roots are rarely seen in full. Both sources describe the same signs of decline and give steps for confirming the cause. This guide follows their advice and notes where they differ.

Quick answer

• Look first for above-ground decline: slow growth, yellow or wilting leaves, scorched leaf margins, and dieback. Purdue says these symptoms are vague, and that root problems are frequently under- and misdiagnosed.
• Check the base of the trunk for dark brown discolored wood, and look for mushrooms, conks or white fan-shaped fungal growth under the bark. Maryland lists these as signs of root rot.
• To look at roots, carefully excavate and wash them. Healthy and rotted roots look different: Purdue says rotted roots “appear water soaked, and are discolored and soft.”
• When the signs fit, submit samples and photos to a diagnostic lab. Purdue says a diagnosis is needed to choose the right management.

Why root rot is hard to see

Root rot often develops out of sight. Purdue explains that “unusually wet weather results in poor root growth, predisposing plants to problems,” because the plant “failed to develop an extensive root system because water was too easily acquired.” During these periods, the source says roots “may even leak, attracting opportunistic fungi and water molds that infect and rot roots.” The infection can be invisible above ground until a dry spell arrives.

When the weather turns dry, the damaged roots cannot support the crown. Purdue describes a sequence in which “the poorly developed and/or infected roots that grew during the wet periods can no longer support the aboveground plant.” The result is what the source calls vague symptoms, including “slowed growth, decline in the crown, smaller leaves that may or may not be chlorotic, heavier seed crops, and the simple description ‘It just doesn’t look good.'”

Purdue also warns that once decline starts, secondary insects and opportunistic fungi attack the plant and are then blamed for the poor health. It describes a “negative feedback loop” in which “dying leaves fail to support dying roots.” That is why a tree with secondary insects may still have a root problem underneath.

Look above ground first

Both sources start with the canopy and stems. Purdue lists these above-ground symptoms of root death: root rot infected plants, “particularly those with multiple shoots, may show healthy, diseased and dead branches,” along with slower growth, yellow and wilted leaves, leaf scorch where the margin of the leaf turns brown, and small shoots or large side branches that are dying or dead. It also lists cankering and dieback of shoots, branches and stems.

Maryland’s page uses different wording for many of the same signs. It says symptoms include poor growth, loss of healthy needle color (needles that “eventually turn light yellow or brown”), “dark brown discolored wood at the base of the stem for several inches above the soil line,” and “loosening and separation of the dead lower bark.” It also lists slowed growth, smaller than normal needles on evergreens, excessive cone or seed set, premature autumn color, and winter twig dieback.

The Maryland page notes that “infected plant material often has extensive dieback.” Purdue also notes that leaf scorch happens whenever a plant cannot obtain sufficient water, so scorch alone does not identify root rot. A dieback pattern alone does not identify the disease.

Check the base for signs of fungi

Fungal growth at the base of the tree is one of the clearest signs. Maryland says that “white fans of fungal growth, and dark brown shoestring-like threads called rhizomorphs may be found under the bark at the base of infected plants, or on the roots.” It describes the fruiting bodies as either “fleshy mushrooms that appear annually” or “hard shelf-like structures that grow a new layer each year as the rot progresses.”

Purdue says signs of root rot “may include fungal structures that are visible to the naked eye,” and names mushrooms and conks. It notes that other signs require microscopic observation. Its figure of a Ganoderma conk on the roots of a pin oak shows a sign that can be found at the root zone. Visible fungi suggest a root problem, but they do not tell you which organism is responsible, so a sample is still the reliable next step.

Purdue lists the primary causal agents of woody plant root disease as macrofungi such as Armillaria, Fomes and Ganoderma, along with some microfungi and water molds in the genera Phytophthora and Pythium. The source states that “regardless of the type of organism causing root rot, they all can survive on dead and dying tissue.”

Expose and examine the roots

Purdue gives the most specific method. It says that “whenever possible, carefully excavate roots, and wash them.” Because “100% of the root area is rarely infected,” the source recommends extensive sampling. It advises using a hand trowel or small shovel to remove multiple samples of about one cup each. The samples should include soil, larger woody roots and small feeder roots, and they should come from at least three locations around the tree.

The source describes the sampling pattern in detail. Samples should be taken “from at least three sides of the affected tree,” and should include “areas within the dripline, by the main stem, and somewhere in between.” Purdue also says that “any suspicious areas (crown rot, mushrooms, conks, fruiting bodies) should be included in the sampling.” Store the samples in a plastic bag, “preferably in a cooler with ice to keep from drying out.”

Purdue also gives a visual test for a dead root. It says the examiner should “always make sure you know what normal roots look like.” Rotted roots “appear water soaked, and are discolored and soft.” The Purdue guide shows a comparison between rotted and healthy roots, and Maryland says that as the infection spreads, “the root system is reduced and dark brown.”

Purdue warns that examining the roots of established woody plants “is difficult, and may not be possible in all situations without a tree care professional.” For large trees, the source suggests that a professional may be needed to expose the roots safely.

Look for structural problems that mimic root rot

Purdue says that after the soil is removed from the base of the tree, the examiner should evaluate whether several problems are present. These include excessive mulch, planting too deeply or too shallowly, significant root or root flare damage, stem or root girdling, few main roots or roots on only one side, feeding damage, galls, and root rot itself. Several of these can cause the same above-ground decline, so the base should be checked for all of them at once.

The depth of planting is one example. Purdue lists it as a condition to check, and Maryland’s page says that “avoid planting trees and shrubs in poorly drained compacted soils or in low areas where water collects.” These conditions can make a tree more likely to develop root disease, so they belong in the same inspection.

Send samples for a diagnosis

Purdue says that diagnosing a root rot “requires observing the affected plant for symptoms, and collecting the infected tissue at the right time to culture out the pathogen or pathogens causing the problem.” It recommends that “samples, along with photos of the tree or shrub, should be submitted to the Purdue Plant & Pest Diagnostic Laboratory for diagnosis.” The source explains that this step is needed because “a diagnosis of the root rot is necessary to develop an effective management plan, including the right fungicide, appropriate cultural controls, and what other nearby plants may be susceptible.”

Maryland’s page makes a similar point. It says that “many fungi can be found on dead and dying trees and shrubs,” which means that finding a fungus is not in itself proof of root rot. A lab culture or microscopic check is the way to identify the organism. Purdue also warns that root disease diagnosis is “more easily said than done,” so the sampling needs care.

Prevent the problem and decide what to do next

Prevention is the main approach in both sources. Maryland says that “there are no cures once the tree or shrub is infected,” and that root rots can be prevented by proper planting and maintenance. It advises avoiding “damage from improper pruning, lawn mowers, and excavation within the root zone.” It also says to avoid planting trees and shrubs in poorly drained compacted soils or low areas where water collects, and to keep plants away from downspouts.

Purdue’s guidance is similar. For Phytophthora-susceptible plants, it says to avoid heavy clay, poorly draining soil, downspouts and low spots that collect water. For Armillaria, it recommends removing stumps completely, for example by grinding, to deprive the fungus of a food source. Purdue also says that some root rots, such as those caused by Phytophthora, “are treatable, if caught and diagnosed early enough.” The two sources differ on this point. Maryland says there are no chemical cures, while Purdue describes treatment as possible in some cases and warns that success depends on the host, the pathogen and the site.

Purdue notes that “damage occurred over several seasons, and recovery may take just as long.” Purdue says that “in some instances, saving a tree or shrub simply isn’t possible or cost effective,” and that a replacement can be chosen from a more resistant or immune host. Before replanting in the same spot, it advises correcting any cultural problems that contributed to the failure.

For a related look at how roots respond to wet soil, see how clay holds water in soil. For one of the root diseases Purdue links to poorly drained soil, see how Phytophthora spreads through soil.

How we chose these sources

We chose two university extension resources that address root rot in trees and shrubs. Purdue Extension’s Plant Pathology in the Landscape Series guide, “Root Rot in Landscape Plants” (BP-206-W, authored by Janna Beckerman and Tom Creswell), covers diagnosis, sampling and management in detail. The University of Maryland Extension page, “Root Rots on Trees and Shrubs” (updated February 28, 2023), covers symptoms, pathogens and prevention. Both were opened on 2026-10-27, and quotations come from the text returned on that date.

The Purdue guide is a longer, more detailed publication, and the Maryland page is a shorter summary. The two agree on the main signs and on prevention, and they disagree on whether root rots can be treated. The guide reports both positions and does not choose one.

What we could not verify

The sources describe signs, sampling steps and prevention. They do not give a test that a homeowner can use to confirm root rot without excavation, and they do not say how to tell a root rot from a root injury by sight alone.

What the sources do not say

Neither source gives a specific fungicide, a dosage or a product for root rot, and this guide does not name one. The sources do not give a number of samples that guarantees a diagnosis, and they do not say how long a treated tree will take to recover. Purdue says recovery “may take just as long” as the damage, but it does not give a number of years. A certified arborist or the Purdue lab can address these questions for a specific tree.

Frequently asked questions

What are the first signs of root rot in a tree?

Purdue describes vague first signs, including slowed growth, smaller leaves, yellow or wilted leaves, leaf scorch and dieback. Maryland adds dark brown discolored wood at the base of the stem and loosened, separating bark.

Are mushrooms at the base of a tree always root rot?

No, but they are a sign to check. Purdue says mushrooms and conks are visible fungal structures that can indicate root rot, and it recommends including them in sampling. Several fungi can be found on dead and dying trees, so a lab identification is needed.

How can rotted roots be recognized?

Purdue says rotted roots appear water soaked and are discolored and soft. Compare any suspect root with a healthy one, because the source says examiners should always know what normal roots look like.

Can roots be dug up without a professional?

Purdue says to excavate roots carefully and wash them when possible. It also says that examining roots of established woody plants may not be possible without a tree care professional, so large trees may need one.

Can root rot be cured?

The sources disagree. Maryland says there are no chemical cures once a tree is infected. Purdue says some root rots, such as Phytophthora, are treatable if caught and diagnosed early enough, and it notes that success depends on several factors.

Sources

• Purdue University Extension, Botany and Plant Pathology, “Root Rot in Landscape Plants,” BP-206-W, https://www.extension.purdue.edu/extmedia/BP/BP-206-W.pdf (opened 2026-10-27).
• University of Maryland Extension, “Root Rots on Trees and Shrubs,” https://extension.umd.edu/resource/root-rots-trees-and-shrubs (opened 2026-10-27).