Red maple is one of the most planted trees in North America. The Morton Arboretum calls it widely adaptable, and it is, but that popularity means many red maples end up in tough spots: tight parkways, compacted new-construction lots, hot parking strips. When a red maple starts losing branches or its leaves look wrong, the cause is usually stress from the site, a root problem or one of a handful of diseases. Working out which one tells you whether the tree can be saved.

Table of Contents

The short answer: the most common reasons red maples decline are stress from drought, compaction and poor sites; girdling roots that strangle the trunk at the base; verticillium wilt, a soil-borne fungus that makes branches wilt and die, often on one side; bacterial leaf scorch, which browns leaf edges on certain branches in midsummer; and root or trunk rots. Check the base of the trunk for girdling roots and a missing root flare, look for green to dark streaks in the wood of dying branches, and have a certified arborist assess any tree with fungi or large dead limbs.

Signs of a red maple in trouble

Leaves smaller and paler than usual, or browning at the edges in summer.
Early fall color, sometimes in July or August, on part of the tree.
Dead branches at the top or on one side.
Thinning crown with fewer leaves each year.
Cracks, cankers or oozing on the trunk.
Mushrooms or shelf fungi at the base.

1. Decline from site stress

Penn State Extension describes maple decline as slowing growth followed by branch dieback until much of the tree is dead. It lists the usual causes, often in combination: poor soil aeration and drainage, deicing salt, high temperatures at the site, drought, excavation damage, soil compaction, paving close to the tree, verticillium wilt and Armillaria root rot.

The Morton Arboretum notes that red maple is moderately sensitive to drought and intolerant of pollution, and that it needs plenty of room for its dense, spreading root system. A red maple squeezed between a driveway and a sidewalk often struggles.

What helps:

Deep watering in dry spells. The Morton Arboretum advises checking the soil with a trowel and watering slowly at the drip line when the top inch or two is dry.
A wide ring of mulch, kept off the trunk.
Protecting the root zone from vehicles, construction and new paving.

2. Girdling roots

Girdling roots wrap around the trunk or major roots and slowly cut off the flow of water and nutrients. They are common on maples planted too deep or grown too long in a container.

Look at the base of the trunk. A healthy tree flares out where it meets the soil. The University of Maryland Extension points to a trunk that goes straight into the ground like a telephone pole, with no flare, as a key sign. A root curving across the base is another. Symptoms above ground are a thin crown and dieback, often on one side. An arborist can remove soil around the base to check and, if appropriate, cut a girdling root.

3. Verticillium wilt

Verticillium wilt is a soil-borne fungal disease of the water-conducting tissue. The Morton Arboretum lists maple among the most commonly infected trees, and lists it as a potential problem for red maple. Symptoms can be sudden or slow. One or more branches may wilt suddenly in midsummer, or leaves may yellow or brown at the edges before wilting.

Penn State Extension adds some telltale signs: heavy seed production, smaller than normal leaves, browning leaf margins and wilting on only one side of the tree. The wood under the bark of a wilting branch shows green to black streaks. Only a lab test can confirm the disease.

Penn State’s advice: prune out affected limbs and water to keep the tree vigorous when symptoms are mild, avoid heavy fertilizing, and do not replant a susceptible species where a tree was killed by verticillium. Some trees recover.

4. Bacterial leaf scorch

Penn State Extension describes bacterial leaf scorch on red maple as leaf margins browning on individual branches in mid to late July, with a dark reddish-brown band and a narrow yellow halo between the brown and green tissue. Leaves may drop in August. The bacteria are spread by leafhoppers and spittlebugs. There is no cure; keeping the tree free of stress helps it cope.

This differs from drought scorch, which browns leaf edges all over the sunny side of the tree at once.

5. Cankers and root rots

Penn State Extension describes bleeding canker on maples as reddish-brown sap oozing from sunken bark on the trunk or branches, with wilting and dieback. It also lists several root and butt rots, including Ganoderma, which forms varnished, reddish-brown shelves, and notes that a tree with fungal fruiting structures on the trunk or roots should be removed promptly if it could hit property or people.

Problems that look serious but are not

Tar spot: shiny black spots on leaves of red and silver maples. Penn State says no control is needed. See black spots on maple leaves.
Anthracnose: brown blotches along leaf veins after a wet spring. Usually little damage.
Maple bladder gall: small red bumps on leaves, caused by mites. The Morton Arboretum lists it among red maple pests; it is cosmetic.

Symptom guide

What you see	Likely cause
Slow thinning, dieback over years, compacted or paved site	Site-stress decline
Trunk without a flare, root across the base, one-sided dieback	Girdling roots
Sudden wilting of one branch or one side, streaked wood	Verticillium wilt
Leaf edges brown on certain branches in late July, yellow halo	Bacterial leaf scorch
Sunken bark oozing reddish sap	Bleeding canker
Shelf fungi or mushrooms at the base	Root or butt rot

When to call an arborist

Call a certified arborist if more than a quarter of the crown is dead, if you suspect girdling roots or verticillium wilt, or if there are fungi, cracks or cankers on the trunk. For more help, see why my maple tree is dying, what’s wrong with my maple tree and why a maple is not leafing out.

Sources

Red Maple, The Morton Arboretum
Maple Diseases, Penn State Extension
Verticillium Wilt, The Morton Arboretum
Girdling Roots, University of Maryland Extension
Watering Trees and Shrubs, The Morton Arboretum

Top photo: Willow, CC BY 2.5, via Wikimedia Commons

Why Is My Red Maple Tree Dying?