Verticillium Wilt, a Soil Pathogen

Verticillium wilt is a soil-borne pathogen that affects 300+ plant species. The name is derived from two types of fungus: Verticillium albo-atrum and Verticillium dahliae. Trees, crops and woody ornamentals can all succumb to this devastating fungal disease. Plants affected with verticillium wilt may decline or die. Annual plants often die quickly, while large trees may experience a slow decline over several years. In Idaho we commonly see verticillium wilt affect maple and ash trees, elderberry, lilac, viburnum, roses, tomatoes, potatoes, mint and peppers, just to name a few. It is also an important disease in Idaho potato production and landscape trees.

This fungus starts in the soil and infects plant roots. It then spreads through the plant’s vascular system, affecting the xylem and its ability to take up water and transport nutrients. The fungus survives in the soil as tiny resting structures (microsclerotia), which can persist for many years, even without a host plant.

Symptoms The infection is marked by sudden wilting of branches, often on one side of the plant. Other common symptoms include faded green or yellowing foliage, browning leaf edges, and stunted growth. You will eventually see dieback in branches.

During periods of heat or drought stress, symptoms often become more noticeable. Plants may wilt even when soil moisture is adequate.

If you cut open a branch of an infected plant, you may notice dark staining following the wood grain—an indicator of vascular involvement.

Quick identification tips:

• Wilting on only one side of the plant or branch
• Yellowing or browning leaves
• Branch dieback
• Dark streaking in the sapwood

Note: Verticillium wilt can be confused with drought stress, herbicide damage, or other diseases such as Fusarium wilt. A laboratory diagnosis is sometimes needed for confirmation.

How Does it Spread? Verticillium wilt is primarily spread through contaminated soil and plant material. The fungus moves when infested soil is transported on tools, shoes, plant roots, or transplants. It can also spread through root contact between plants and by moving soil with water runoff or equipment. The disease is rarely spread aboveground. Insects such as aphids may stress plants or create wounds, but they are not considered a primary means of spreading this disease.

How to Manage Verticillium Wilt In most cases, it is best to remove infected plants, as there is no cure once a plant is infected. If there is limited dieback in tree branches, a certified arborist may be able to prune out affected wood. If you remove affected branches, be sure to clean your pruners between cuts to avoid spreading contaminated soil or plant material.

You can sanitize tools with a 10% bleach solution (1 part household bleach to 9 parts water). Keep in mind bleach solutions lose effectiveness over time and can be corrosive to tools, so rinse and dry tools after use.

Verticillium can remain in the soil for many years, so replanting requires careful plant selection. Choose plant species that are resistant or less susceptible to verticillium wilt.

Crop rotation for 3–5 years may help reduce disease pressure, especially in vegetable gardens, but it may not eliminate the fungus due to its long survival in soil.

Additional management tips:

• Avoid planting highly susceptible species in infested areas
• Rotate with non-host plants such as grasses when possible
• Maintain healthy soil and proper irrigation—stressed plants are more susceptible
• Avoid damaging roots during planting or cultivation
• Remove and dispose of infected plant material (do not compost unless at high temperatures)

For vegetables like tomatoes, look for resistant varieties labeled “V” or “VFN.”

Does your tree look like this?

Damage is often patchy.

Have you ever noticed a tree with a branch that turns brown midway through the season while the rest look fine? Or a vegetable plant with stems turning yellow and brown?

What is it?  

Verticillium Wilt (Vw) V. dahliae  and Verticillium albo-atrum  is a soil borne disease that spreads through the roots to a plant’s vascular system. It can stump a gardener with early drought-like symptoms. It is a fatal disease of many important agricultural and horticultural crops. It is particularly present wherever potatoes and mint were farmed. And it can even kill a tree.

What does Verticillium Wilt look like? 

Vw symptoms can include wilt, chlorosis, reddish to purplish discoloration of leaves or stems and brown-stained or stunted leaves and vary widely between species.See video.

Vw on Maple

If you think your plant is infected, first find out whether that species is a host. Plants Resistant Or Susceptible To Verticillium Wilt, developed by the University of California, is a good resource. 
Proper diagnosis requires laboratory testing to rule out other organisms. Homeowners can submit a sample of soil to find out the level of Vw in the soil. The cost is $50.00 for plant material sample and $105.00 for the soil testing at the University of Idaho Plant Disease Diagnostics Lab in Parma, Idaho. Be sure to contact the lab first for specific instructions at (208) 722-6701.

What Types of Plants are susceptible?

Vw affects over 300 species. Trees most commonly and severely affected are maple and ash. The list also includes red-bud, lilac, catalpa, and smoke-bush.

Vw on dahlia

Vw on blackberry

Annuals, including dahlia and sunflower can be infected, as well as garden plants like cantaloupe, tomato, and asparagus. Once affected, roots may not develop normally again.

Dr. James Woodhall, Assistant Professor and Plant Pathologist with the U of I Parma Research Center says Vw is patchy – particularly in maples, but also as it appears throughout your property. Not every inch of ground will have it.

How do I save a tree or shrub with Verticillium wilt?  

Trees and shrubs infected with this systemic disease cannot be cured. They may die quickly in one season or slowly over several years. However, you can extend the life of your plants by making sure that you water and fertilize properly. 

In woody host plants, pruning of symptomatic limbs to remove all discolored sapwood, followed by burning, has prolonged the life expectancy of some trees.

If you remove a plant or tree because of this, be sure to plant a high value tree in some other field. This fungal genus may remain alive in the soil for many years in a resting state.

Can I Prevent Verticillium damage in the future?

The best way to avoid Vw is to plant deciduous trees and shrubs that are immune or resistant. You may have seen some or all of the letters VFNT next to the names of hybrid plant varieties in catalogs and on seed packets. The name will have a V following the variety name if it is resistant to Vw. Always test the soil before planting, especially with high value trees. Purchase disease tolerant trees and plants.

Brian Hudelson, UW-Madison Plant Pathology advises not to use mulches that may have been produced from infected trees or have unknown composition. Finally, immediately collect and discard leaves that have fallen from symptomatic trees.  Both mulch and leaves are potential sources of Verticillium.