Identification

Early signs of Verticillium wilt include leaves turning yellow, wilting and leaf drop which often affects one side of the plant more than the other. The presence of the disease can be confirmed by cutting into the stem of the infected plant and looking for dark, discolored streaking or rings present within the vascular tissues. This is evidence of the fungus starving the plant of its  necessary hydration and nutrients.

Life Cycle

Both Verticillium dahliae and Verticillium albo-atrum survive in soil and plant debris as microscopic structures called microsclerotia. These structures can lie dormant for years until they come into contact with the roots of a suitable host plant. These microsclerotia germinate, infecting the plant through its root system, causing the symptoms associated with Verticillium wilt. The fungus continues to produce more microsclerotia within the plant tissue, which can be returned to the soil as the plant decomposes, perpetuating the cycle of infection.

Distribution & Habitat

Verticillium thrives in temperate climates, affecting plants in a variety of environments. Specifically, Verticillium albo-atrum is found in cooler soils while Verticillium dahliae is found in most soils across the globe. The affected host plants include maple, ash, elm, magnolia, lilac, redbud, dogwood and certain fruit trees.

Damage & Symptoms

The damage from Verticillium wilt is internal but undistinguishable until the external symptoms start to show such as wilting, discolored leaves, stunted growth, branch dieback and eventual death of the plant. Symptoms can be intensified with the added stress of high temperatures, making the loss of water that much more devastating to the health of the affected trees and shrubs. Infected trees and shrubs may show signs of recovery but can be reinfected, contributing to plant death.

Management & Control

The best way to manage and control Verticillium wilt is using integrated pest management (IPM) strategies. Once a plant is infected, there is no cure so early detection and removal of infected trees and shrubs is crucial to success.
Start with soil fumigation and planting resistant varieties of trees and shrubs. If this is not possible, take care to reduce the stress on existing plants by following the recommended guidelines for watering, mulching and fertilizing. Preventive measures are especially essential, because there are no known biological controls for Verticillium wilt and fungicides are generally ineffective once a plant is infected.

Prevention

Prevention is the main defense against Verticillium wilt. Selecting resistant varieties when planting new trees and shrubs can significantly reduce the risk of infection. Follow this with proper plant care to maintain good health and make trees and shrubs less vulnerable to diseases. Regular monitoring and early detection will also go far in preventing the spread of the fungus species and the diseases they cause.

Are Your Trees and Shrubs Suffering From Verticillium?

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