Verticillium wilt

What is Verticillium wilt?

Verticillium wilt of trees and shrubs is caused mainly by the soil fungus Verticillium dahliae. It enters through roots, often through small wounds, and grows into the water-carrying wood. The tree plugs its own vessels in response, which cuts off water to branches and leaves.

Maples are among the most common victims, especially sugar, red and Japanese maple. Catalpa, redbud, smoketree, magnolia, ash, tuliptree, black locust, elm, viburnum and many others can also get it. Conifers are resistant, and so are many hardwoods such as birch, ginkgo, honeylocust, sweetgum, white and bur oak, and crabapple.

The fungus forms tiny resting bodies (microsclerotia) that UMass says can let it last in soil for more than a decade. It spreads through soil, root contact, wind-blown infected leaves, symptomless weeds and chips from infected wood. Iowa State says it can kill a tree in one growing season, while Penn State says large trees may live for years with minor symptoms but are often killed within 2 to 3 years. Once a site has it, replanting with resistant species is the practical fix.

Plants it infects: sugar maple, red maple, Japanese maple, northern catalpa, eastern redbud, smoketree, magnolia, ash, tuliptree (tulip poplar), Kentucky coffeetree, black locust, viburnum, elm.

Symptoms and signs

• Leaves on one branch or one side of the tree wilt, yellow or brown at the edges, and dry up
• Scattered branch dieback in an otherwise healthy-looking tree
• Smaller than normal leaves, sparse foliage and slow growth in chronic cases
• Green, olive or brown streaks in the wood under the bark of wilting branches
• Heavy seed crop on a stressed tree

Verticillium wilt identification: what to look for

• Symptoms: Leaves wilt, yellow, scorch at the margins and dry, often on one branch or one side of the canopy.
• Damage: Streaks in the sapwood under the bark of wilting branches: green to black or olive-brown in maples, brown in elms, and brown to black in black locust and other trees (Penn State, Michigan State). Ash rarely shows streaks, and Iowa State notes streaking is not always present.
• Symptoms: Chronic cases show small leaves, sparse foliage, slow growth and a heavy seed crop.
• Timing: Symptoms can appear any time in the growing season; UMass says they often first show around mid-June.

Disease cycle

The fungus survives in soil and dead plant tissue as tiny resting bodies. It enters through wounds or natural openings in roots or the trunk base and spreads in the water-carrying wood. The tree plugs some of its water vessels with gums and other materials, which cuts water flow further. Infected leaves and stems that fall into the soil let it overwinter there. It can also move by root contact, wind-blown infected leaves, symptomless weeds, and chips or compost made from infected wood.

When to look: Michigan State says leaf symptoms are most likely in July and August under water stress; UMass notes they often first show around mid-June.

Verticillium wilt look-alikes

A few things get mixed up with it:

• Drought or root damage: UMass says root disease, root damage and drought stress can look the same. Streaks are not always present, so a lab test separates them.
• Girdling roots or soil-applied herbicide damage: Iowa State lists these as common lookalikes.
• Branch cankers: UMass lists branch cankering as a look-alike, since cankers also starve branches of water.

How to manage Verticillium wilt

Cultural control

• For mild cases, prune out dead and wilting branches, disinfecting tools between cuts (Iowa State).
• Water regularly in dry weather and keep the tree healthy. Penn State also suggests fertilizing a mildly affected tree to maintain vigor.
• Never use chips or compost from an infected tree as mulch or potting mix.
• Do not replant susceptible species where a tree died of Verticillium wilt. Choose resistant trees such as conifers, honeylocust, ginkgo, sweetgum, birch or white oak.
• Avoid wounding roots and the trunk flare during construction or yard work.

Chemical control

There is no reliable cure, and Michigan State says fungicides are not effective against this disease. UMass says fungicides usually do little once symptoms appear, though trunk injections of debacarb, carbendazim, phosphites, propiconazole or tebuconazole may slow spread in trees that can recover. Penn State says benzimidazole injections give unpredictable results, and soil fumigation by a licensed applicator reduces but does not eliminate the fungus. Use only products labeled for this use; the label is the law. Injections must be done by an ISA Certified Arborist with a pesticide applicator license (see pesticide applicator license guide).

Use only products labeled for this disease and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Plant resistant species on sites with a history of the disease.
• Do not bring in wood chips from unknown or diseased trees.
• Keep susceptible trees watered in drought.

When to call a pro

Call an ISA Certified Arborist if a maple or other susceptible tree starts wilting on one side. An arborist can collect live branch samples for a lab, prune safely, and advise whether the tree can be kept. Iowa State says to send 3 to 6 living, wilting branches, kept cool and delivered fast.

Related guides: Tree database: mature size and planting distance · Pennsylvania tree identification · Firewood rules by state · All pests and diseases

Questions about Verticillium wilt

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