Verticillium wilt is a fungal disease that attacks a wide variety of woody plants. It is caused by the fungus, Verticillium dahliae Kleb, which survives in the soil where it may remain dormant for many years.

When the roots of susceptible plants become infected, the fungus grows upward in the water conducting vessels. As they enlarge, the flow of water is inhibited and the part of the plant dependent on those vessels will begin to wilt. In advanced cases, branches will die back and eventually, the whole plant may be killed.


Plants infected with verticillium wilt will show both external and internal symptoms. In the early stages, external symptoms may include yellowing foliage, leaf scorch, twig die back, sparse foliage or abnormally heavy seed production.

In advanced cases, plants will exhibit rapid defoliation, wilting and death of leaves on individual branches. Symptoms may appear on only one branch or section of the plant or sudden wilt of the entire crown and death of the plant may occur, especially in hot, dry weather.

Infected plants may show increasing symptoms over several years or may not have any symptoms the following year and appear to recover completely. A plant may be infected for a long time before noticeable symptoms appear.

Internal symptoms of verticillium wilt consist of streaks or bands of discolored "stain" in the sapwood beneath the bark. This discoloration becomes apparent when dead branches are cut off the plant.


The most effective way of dealing with verticillium wilt is to avoid it. There are many ornamental plants that are resistant to the disease. If a plant dies of this soil borne wilt, it should be replaced with one that is resistant. Also, avoid those that are known to be susceptible.

Ornamental plants RESISTANT to Verticillium wilt:


Generally, plants that are severely infected and showing symptoms throughout the crown cannot be saved. Plants with less severe symptoms, however, may recover.

To help trees combat this disease, keep them adequately watered throughout the summer. They need about an inch of water per week in either rainfall or irrigation. If there is a dry period, place a hose beneath the tree and let the water trickle gently for several hours so that the water will soak deep into the ground. Do not allow the water to runoff the surface.

Proper fertilization may help trees fight verticillium wilt in the landscape. A balanced fertilizer such as a 12-12-12 or 10-10-10 (N:P:K) should be applied.

It is important to apply a fertilizer with potassium (K) to plants suffering early stages of Verticillium wilt. Do not apply lawn fertilizers such as 45-0-0 (Urea) or 27-3-3 since these high nitrogen products may actually worsen the wilt problem.

Trees and showing early symptoms should be fertilized yearly in the early spring once the frost is gone from the ground. Do not fertilize these plants in the summer or fall.

Using an auger drill bit or post hole digger, make holes about 12 inches deep and in circular patterns around the tree. Start at least about 3 feet from the trunk to avoid damaging major roots and extend out to the drip line of the tree. Apply fertilizer at the rate of 6 lbs. of nitrogen per 1,000 square feet of area and refill the holes with peat moss.

 Prune out and destroy dead and dying branches but not those that have recently shown signs of wilting. They may come back the following growing season.

Remove dead trees along with as much of their root system as is possible. Do not bury the debris or use the wood chips from infected plants.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Ornamental plants SUSCEPTIBLE to Verticillium wilt:

 

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