Tree problems · Disease

Armillaria root rot (shoestring root rot): signs and what to do

Armillaria root rot (shoestring root rot) is a tree disease, often seen on white oak, northern red oak, pin oak. Look for: thinning crown, small leaves and slow growth over several years.

General information, not a diagnosis. A certified arborist or your county extension office can confirm.

Disease
White oak
Northern red oak
Pin oak
Sugar maple
Red maple
Eastern white pine

Signs to look for

Tick what you see. More ticks make it more likely, but only an on-site look can confirm.

Thinning crown, small leaves and slow growth over several years
Yellowing or early fall color, and branch dieback
White fungus sheets (mycelial fans) under the bark at the base of the trunk or on roots
Dark, shoestring-like strands (rhizomorphs) on roots or in the soil near the root collar
Clusters of honey-colored mushrooms at the base of the tree in fall, though not every year
Resin flow or bleeding at the base of the trunk on some trees, and root decay

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Season

The rot works year-round underground. Honey-colored mushrooms often show in late summer and fall. Crown decline is easiest to see in summer.

How it spreads

The fungus spreads through the soil by dark rootlike strands and by root-to-root contact. It lives on dead roots and stumps and attacks trees weakened by drought, defoliation or other stress.

Where it is found

Armillaria fungi are found in forests and landscapes across much of the United States, and different species vary in how aggressive they are. Check your state official map; ranges change.

Official sources

What to do

1
Have an arborist look at the root collar. Brushing back soil at the base can show the white fans or black strands.
2
Water deeply in dry spells and avoid more stress, such as soil piled on the roots or lawn work that hurts roots.
3
Remove dead and declining trees that are a danger. Root decay can make a tree fall without warning.
4
When a tree is removed, take out as much of the stump and large roots as practical, since the fungus feeds on them.
5
Replant with a species that is less affected. Ask a local extension office which kinds do well on your site.

Safety first: do not climb, do not cut near power lines and do not use a chainsaw on storm-loaded wood. Call the utility for downed lines and 911 if anyone is in danger.

Prevention

Keep trees healthy: plant the right tree in the right place, water in drought, keep mulch off the trunk, and avoid root damage and grade changes. Stressed trees are the ones most often attacked.

When to call a pro

Call an arborist right away if a tree has mushrooms at the base, a thinning crown and a lean, or if it is near a house, driveway or play area. Rotted roots can make a tree fail even when the crown looks fine.

Not sure who to call? Read how to hire a tree service or check is my tree dangerous?

Trees it affects

Usually seen on: White oak, Northern red oak, Pin oak, Sugar maple, Red maple, Eastern white pine, Douglas fir, Black cherry.

See all species in our tree library, or pick a tougher tree with the tree picker.

For tree companies

How to explain Armillaria root rot (shoestring root rot) to a customer

Explain that root rot is hidden, so a ground-level check is the key. Be honest that no spray cures it and that safety is the main point. Avoid scare tactics: show the signs, state the risk, and let the customer choose between monitoring and removal.

Send this page to the customer after your visit so they can read the signs in plain words. See also selling plant health care and the job photo checklist.

Questions

Are the mushrooms at the base always Armillaria?

Honey-colored clusters at the base are a common sign, but other fungi look similar. An arborist can confirm by checking under the bark and on the roots.

Can a tree with Armillaria be saved?

Sometimes a tree with mild infection can hold on for years if its care improves. Trees with a lot of root decay are often not savable, and they may become unsafe.

Is it the same as shoestring root rot?

Yes. 'Shoestring' comes from the dark, stringlike strands the fungus grows on roots and in the soil.

Can it spread to other trees?

It can move through the soil to nearby susceptible trees, especially stressed ones, and it can live on old stumps and roots.

Will a fungicide help?

There is no reliable treatment for a tree already infected. Prevention through good care is the focus.

Is the tree dangerous?

It can be. Root decay weakens how the tree stands up in wind or wet soil. If it is near people or buildings, get a professional risk check.

Can Lirevon diagnose Armillaria root rot (shoestring root rot) on my tree?

No. Lirevon is a remote marketing team for tree service companies and does not do tree work. This page is general information, not a diagnosis. A certified arborist or your county extension office can confirm what is wrong with your tree.

How do I find a good local pro for this?

Search Google Maps for certified arborists or tree services near you, read their reviews and ask for proof of insurance. Get two or three written quotes. Our guide on how to hire a tree service lists the questions to ask.

When customers spot Armillaria root rot (shoestring root rot), they call

Make sure someone answers. Missed-call text-back, lead follow-up, booking and review requests, set up for you. See our services and pricing.

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