The stress of hot, dry conditions in midsummer can prompt leaf scorch in many landscape trees. However, extensive canopy dieback or tree collapse, particularly on one side of a tree, may indicate Verticillium wilt disease. Numerous cases of this vascular wilt disease have been confirmed by the UK Plant Disease Diagnostic Laboratory (UK-PDDL) in recent weeks.
Verticillium wilt can affect a wide range of ornamental trees and shrubs, resulting in branch dieback, decline, and eventual tree death. Since numerous environmental stresses, including heat and drought, can result in similar symptoms, lab confirmation is recommended. County Extension agents can assist in preparing a sample for submission to the UK-PDDL. While there is no cure for Verticillium wilt, proper plant care may prolong the life of infected trees with mild symptoms. Furthermore, a confirmed diagnosis of Verticillium will assist homeowners and landscape professionals in making the best choice of tree or shrub for replanting
Verticillium Wilt Fast Facts
Symptoms include dieback and decline of branches scattered over the entire plant; or affected branches may be confined to one side (Figure 1). Leaves may be undersized, wilt suddenly, or exhibit marginal scorch, yellowing or browning (Figure 2). If bark of a limb is removed, a cut into the sapwood may reveal olive-green, brown, or black streaking in the water-conducting tissues of the plant, depending on the plant species (Figure 3). Ultimately, plant death occurs, particularly following drought stress.
The Verticillium fungus can survive in the soil for many years and typically enters plants through the roots.
Over 400 herbaceous and woody plant species have been reported as hosts for this disease. Some common hosts include lilac, maple, catalpa, magnolia, redbud, smoketree, and tulip poplar.
Caused by the fungal pathogen Verticillium dahilae.
The life of plants with mild symptoms may be prolonged through the following plant care steps:
— Prune and destroy symptomatic plant material. Be sure to sanitize tools between cuts.
— Water trees liberally as needed, especially during hot summer months, but avoid overwatering.
— Plants with severe symptoms cannot be saved, and the following steps should be taken to avoid disease spread and further incidence.
— Remove and destroy entire affected plant.
— Avoid moving soil from the infested area to other parts of the landscape.
— Replant with resistant plant species or cultivars.