How to Identify, Control, and Prevent Verticillium Wilt

As a gardener, you have probably heard about the benefits of soil fungi or even have added mycorrhizae into your soil. Unfortunately, not all fungi are beneficial. 

Verticillium wilt is a fungal disease that impacts over 400 plant species including trees and shrubs, vines, flowers, and vegetables. Some of our most prized garden plants, such as roses and tomatoes, are susceptible. 

There are two types of this soil-borne fungi: Verticillium dahliae and Verticillium albo-atrum. These fungi live in the xylem of plants which are tiny tubes that help to transport water and nutrients throughout the plant. They essentially create a blockage in the plant vascular system. Some infected plants may wilt as a result. Verticillium also produces toxins that harm host plants. 

There are currently no treatments available for verticillium, but there are many ways to prevent or manage the disease.

What is Verticillium Wilt?

Verticillium is a common soil fungus that thrives in temperate climates and can be present in the soil for decades.

Verticillium overwinters in the soil as mycelium or tiny black resting structures called microsclerotia, waiting for favorable conditions to return. They enter damaged plant tissue through the roots and multiply.

Many common weeds like dandelions and pigweeds can be host species for verticillium. 

Types Of Verticillium

Verticillium dahliae is found in temperate parts of the world and affects many common garden favorites. These include members of the nightshade family (tomatoes, peppers, eggplants), mints, berries, roses, and maples.

All monocots (tulip, corn, ginger, grass) and all gymnosperms (conifers, ginkgos, cycads) are resistant to this disease.

Compared to Verticillium dahliae, Verticillium albo-atrum has a more limited host range and distribution, including agricultural crops like cotton, alfalfa, and hops. 

Life Cycle of Verticillium

Verticillium belongs to the fungal class Deuteromycetes, which are not known to have a sexual reproduction system. Instead, the verticillium fungi have asexual reproductive spores called conidia.

The name verticillium derives from the Latin word verticillus meaning ‘whorled’. This is because these single-celled conidia are born from specialized hyphae that are arranged in a whorled pattern. 

The fungal spores infect plant tissue and occupy the xylem vessels where more conidia are produced. Conidia move throughout the vascular system as the plant transports water, eventually leading to the narrowing of the xylem. This issue is akin to humans having blocked arteries.

As the xylem becomes blocked, it will not be able to efficiently transport water and nutrients and the plant will wilt. As the plant dies, the verticillium fungi form structures called microsclerotia on the dying plant tissue. These little black dots are typically visible using a handheld magnifying glass. 

Microsclerotia are released into the soil through the decomposition of the original host plant. It contains conidia that can infect other plants through root systems. It can even exist on the surface of resilient plant roots, poised to infect neighboring non-resilient plants.

This disease can also be transmitted through pruning tools, so it’s very important to sanitize your tools between plants. Plants that already suffer from root damage, such as from nematodes, are more susceptible to verticillium wilt. 

Symptoms

In many trees, verticillium wilt is an acute or chronic issue. An acute infection in new wood or sapwood might suddenly cause yellow leaves and die back. In older wood, the tree might develop smaller leaves, leaves that yellow at the edges, and lack of growth. Trees may not die immediately but suffer a slow decline. 

In plants like strawberries and tomatoes, you may see leaves with reddish-brown edges that curl and fall off prematurely. For strawberry plants, the entire crown might die off. This disease travels from the bottom of the plant upwards. New leaves may be yellow and stunted. In tomatoes, you may first notice yellow blotches on the lower leaves. Leaves may turn brown but the stems typically will not, unlike fusarium wilt. 

Control

Although there is no treatment for verticillium wilt, there are several effective mitigation practices. These include soil sanitation, crop rotation, and selecting resilient cultivars. Proper pruning, watering, and fertilization can also better prepare plants to fight against diseases. 

Avoid planting susceptible plants in areas that have known inoculations of verticillium. If you suspect your plants have verticillium wilt, cut off the infected plant tissue. Don’t put them in your regular compost to reduce the spread. Instead, throw them away.

Practicing crop rotation with resistant plants may also help to disrupt the life cycle of the fungi.

Prevention

Plant resilient cultivars and disease-free plants when possible. For example, some readily available types of resistant tomatoes include ‘Red Pride’, ‘Ace 55’, ‘Patio Choice Yellow Bush Cherry’, and more. They are indicated by the letter ‘V’ to show resistance to verticillium wilt.

For strawberries, ‘Camino Real’, ‘Petaluma’, ‘Albion’, and ‘San Andreas’ are more tolerant of verticillium. Check with your garden center to see which cultivars they carry that are resistant to the fungus.

Frequently Asked Questions