Verticillium Wilt

How to Spot, Understand, and Deal With This Tree Disease in Ontario

Young maple tree showing early signs of Verticillium wilt, with brown, wilted leaves on one side of the lower canopy while the rest of the foliage remains green and healthy. Photographed in a grassy Ontario landscape.

If your tree’s leaves are wilting, yellowing, or falling off too early, you may be dealing with a serious fungal disease called Verticillium wilt. This disease affects a wide range of trees in Ontario, and without quick action, it can lead to permanent damage or even tree death.
In this guide, we’ll help you understand what Verticillium wilt is, how to recognise it, what causes it, and most importantly, what to do if you think your tree is affected.

What Is Verticillium Wilt?

Verticillium wilt infects a tree through the roots,

Verticillium wilt is a tree disease that starts in the soil and spreads through a fungus known to damage the plant’s internal water flow. Once the fungus enters a tree’s root system, it travels through the xylem—the plant’s water-carrying tissue—disrupting circulation and slowly starving the tree from within.
It’s a silent killer. Trees often show vague or seasonal symptoms before declining rapidly, which is why early recognition is so important.

How to Spot the Symptoms in Trees

A maple tree displaying classic symptoms of Verticillium wilt, with yellowing and wilting leaves on one side while the other side remains green and healthy. An inset image shows a close-up of a cut branch revealing dark streaks in the sapwood, a common sign of internal fungal infection.

The signs of Verticillium wilt can look like other stress factors (drought, insect damage), but there are a few telltale indicators

  • Sudden wilting of leaves, especially on one side of the tree
  • Yellowing between leaf veins or browning at the leaf edges
  • Branch dieback, especially in the upper canopy
  • Sparse foliage or early leaf drop
  • Dark streaks in the sapwood if you cut into a branch (a sign of vascular damage)

These symptoms tend to appear in summer, especially after a hot spell.

Which Trees Are Most at Risk in Ontario?

Illustrated lineup of trees and shrubs commonly affected by Verticillium wilt in Ontario, including maple, redbud, catalpa, and lilac. Some show mild symptoms such as yellowing leaves or sparse foliage. Set in a grassy park landscape.

In Southern and Central Ontario, we most commonly see Verticillium wilt affecting:

  • Maple trees (especially Norway, Japanese, and silver maples)
  • Ash trees
  • Smoke trees
  • Catalpas
  • Redbuds
  • Elms
  • Lilacs

Fruit trees and some shrubs can also be affected. The disease doesn’t spread between trees through the air, but it does persist in the soil, sometimes for over a decade.

What Causes Verticillium Wilt?

Educational diagram showing how Verticillium wilt infects a tree through the roots, spreads upward via the xylem, and causes dieback. Includes a soil-level view of fungal spores, directional arrows illustrating the spread, and an inset showing darkened vascular tissue within the tree trunk.

The fungus lives in the soil and enters trees through the roots, especially if the tree is already under stress (from drought, poor pruning, or mechanical injury).
Once inside, the fungus multiplies within the xylem, producing toxins and plugging the vessels. The tree responds by trying to block off the affected areas, but this further disrupts water flow and causes dieback.
You can’t see the fungus and won’t smell it either, so it’s important to monitor for symptoms and act fast.

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Can It Be Treated or Stopped?

Currently, no fungicides are available that will cure Verticillium wilt once a tree is infected.

However, infected trees don’t always have to be removed. Here are some effective management strategies:

Cultural Management

Certified arborist in a boom lift pruning a large tree to prevent disease and structural damage before winter

Prune affected limbs during dry weather and sterilise pruning tools between cuts.

Improve soil conditions for tree health: compost, mulch, and deep watering during droughts.

Avoid nitrogen-heavy fertilisers, which can stimulate weak growth.

Remove and replace dead or dying trees with resistant species (oak, birch, beech, etc)

Soil Testing

Gloved hands collecting soil samples for laboratory testing to detect Verticillium Wilt in Ontario trees.

While visual diagnosis is often enough, we can arrange for soil or tissue testing to confirm infection and rule out other causes.

When to Call and Arborist

If you notice wilting or dieback that doesn’t improve, or if the tree has significant dieback already, it’s time to get expert advice. Early intervention can sometimes extend the life of a mildly infected tree.

A certified arborist uses a boom lift to inspect and prune a large tree with signs of dieback near a residential home in Ontario. The tree’s canopy is sparse, and the work is being done safely with professional equipment.

You should contact Sarginson’s Tree Services if:

  • A valuable or mature tree shows symptoms
  • You’re considering pruning or removal, but aren’t sure
  • The tree is near structures or pathways (risk of falling limbs)
  • You’ve had Verticillium wilt before and want to replant safely

Local Considerations for Ontario

Arborist lift positioned to inspect a mature deciduous tree for signs of Verticillium Wilt, including dieback in the upper canopy.

Ontario’s variable weather—wet springs followed by dry summers—creates ideal conditions for Verticillium wilt to spread. In regions like Durham, York, and Peterborough, we’ve seen a noticeable increase in cases over the past decade, especially in suburban gardens with older maples.

If you’ve recently moved into a property with established trees, it’s worth having a health check done before summer stress sets in.

FAQS About Verticillium Wilt

A mature Black Locust tree showing partial canopy dieback, with browning leaves on one side—typical symptoms of Verticillium wilt or vascular stress, photographed in a temperate urban environment.

Possibly—if symptoms are mild and you quickly improve the tree’s health. Pruning and soil improvement can buy time.

Not between trees directly. But tools, root grafts, or moving infected soil can spread it.

Yes, but only with resistant species. The fungus can remain in the soil for years.

Maples, ash, redbud, and catalpa trees are among the most commonly affected trees in Ontario. While conifers are generally safe, many popular deciduous shade trees are susceptible, especially in areas with compacted or waterlogged soil.

There’s no cure for Verticillium Wilt, but not all trees need to be removed. In mild cases, pruning affected branches and improving soil health can help the tree survive. If the damage is widespread or the tree poses a safety risk, removal may be the safest option.

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Verticillium wilt isn’t just a nuisance—it can mean the loss of a tree you’ve cared for for years. But you don’t have to figure it out alone.
At Sarginson’s Tree Services, we’ve helped hundreds of Ontario homeowners identify, manage, and—when necessary—safely remove trees affected by Verticillium wilt. We’ll give you honest advice, backed by experience, and help you choose the safest, most cost-effective path forward.

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