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.”

Butterfly Gardening

A successful butterfly garden will have several key features which create a suitable habitat for butterflies and their larva called caterpillars. The first thing to remember is to avoid using insecticides in your garden, even those considered organic. There are several good alternatives such as soap sprays and horticultural oils.

Next, be sure your garden has the proper water. Create areas where water can puddle, then add rocks in the sun so butterflies can sun and warm themselves. 

Create an easy mini pond and you'll be rewarded with other visitors that will benefit your backyard ecosystem: frogs and birds - bees, too, need water!


Last, add plants which will provide shelter and food throughout the entire season. Butterflies tend to be attracted to brightly colored fragrant flowers.
Plants to consider growing for a butterfly garden in Idaho include bee balm, butterfly bush, cornflowers, dill, lilac, parsley, yarrow, zinnias, and other nectar bearing plants.

For other pollinators that will love your butterfly garden, click below
Bee Habitat
Attracting Native Bees to your landscape

Or I'll huff, and I'll puff, and I'll dry your ground out!

Or I’ll huff, and I’ll puff, and I’ll dry your ground out

One of the trademarks of living in Idaho seems to be wind. Learning how to adapt can be challenging to any newcomer. Unless you are from, say, Chicago? In any case, being aware of how wind affects your landscape can help in protecting them during our often dry, windy fall and winter seasons.

Drying winds strip plants, turf, and the soil of much needed moisture. As the wind blows it wicks the moisture out of the plant, and the soil. As the low humidity and wind blow, plants can’t replenish the water they lose through their leaves, or needles. This is one reason you may have a brown cast on the edge of your evergreen needles.

On perennial shrubs, such as roses or lilacs, damage to terminal growing points can occur.

There are several things to keep in mind about your landscape if you live in these windy areas.

1. Fall and winter watering is not an option. Failure to water your plants is the most common cause of plant stress I see in landscapes. And just because your landscape is mature, does not mean you can stop watering it. You don’t stop drinking water just because you've matured, do you?

2. Mulch can help retain moisture in the soil. Yes, I know, it’s windy and the wind blows your mulch all the way to Kansas. Well, I am sure the people of Kansas appreciate your contribution to their fine state. Really though, mulching can make a big difference in how much water your soils will hold.

3. Add organic matter to your soil. Incorporating 2-3 inches of plant based organic matter at a depth of 4-6 inches will help hold in water if you have sandy soil, or help water drain if you have clayey soil. Either way, adding organic matter such as composted plant material will benefit your plants. Just be careful if you use animal manure as compost as these contain salts and heavy metals that build up in the soil over time, and can increase the risk of food borne pathogens if used improperly in vegetable gardens.

For more information on fall or winter watering, visit your county Extension office.