What is Verticillium Wilt?
Verticillium wilt is a fungal disease resulting in injury or death to numerous types of plants including herbaceous ornamentals, shrubs, trees, fruits, vegetables, vines and ground covers. Verticillium wilt affects the plant tissues conducting water referred to as xylem. The most frequently infected plants include magnolia, catalpa, smoke-tree and maple woody plants.
What Does Verticillium Wilt Look Like?
Verticillium wilt causes a sudden wilting of the tree branches, generally on just one side. The leaf margins often turn brown with a scorched appearance or the leaves can turn yellow prior to wilting. You may see a decline in the growth of new twigs or the appearance of dead branches and twigs. If you have tulip or maple trees, look for elongated sections of dead bark appearing on the trunk or branches.
Diseased trees have internal sapwood discolorations on the most recent rings. Verticillium wilt causes greenish streaks in maples, yellowish-green streaks in smoke-trees and brown discolorations in numerous woody plants. There may not be any discoloration if your tree is younger. If discoloration is present, it will often appear a few feet below the wilting leaves.
Identifying verticillium wilt is difficult, but the belief is the disease takes on two different forms. Depending on the form, your plant may die in a few weeks, or more slowly over the course of several years. The amount of branch wilt may increase yearly or remain the same for several years. Some evidence has shown verticillium wilt can be exacerbated by incorrect nitrogen levels or unbalanced fertilization. The most common symptoms of verticillium wilt include:
- Wilting branches
- Areas of dead bark
- Discolored sapwood
- Green, brown or yellowish-green streaks
- Wilting leaves
What Causes Verticillium Wilt?
The cause of Verticillium wilt is Verticillium dahliae, a type of soil fungus. The other form is less common and called Verticillium albo-atrum. Verticillium wilt takes the form of a fungus living in small dark areas of your soil. This fungus can remain dormant for several years. When the roots of your plant begin growing near the fungus, it will germinate resulting in an infection of your plant using natural openings or wounds.
Verticillium wilt then uses the vascular system of your plant to spread to the branches resulting in plugging of the plant cells. Eventually, your plant will be so plugged, water will be unable to reach the leaves. Verticillium wilt can also spread using wounds located on the trunk or branches.
How to Treat Verticillium Wilt
If your tree is not yet dead, it is possible for verticillium wilt to be outgrown. Unfortunately, no effective treatment for verticillium wilt currently exists.
How to Avoid Verticillium Wilt
Avoiding verticillium wilt is difficult because it can remain in your soil indefinitely. Pruning dead branches will help increase the overall vigor of your plant. You can avoid transmitting verticillium wilt through your pruning tools by sterilizing them in a diluted cleaner. Planting trees in areas appropriate for growth will help avoid stress.
During dry periods, water your plants thoroughly. You can prevent fluctuation in soil temperature and retain moisture with an organic mulch layer three to four inches thick. Use proper fertilization and avoid injuring the branches, trunk and roots. If your plant becomes severely infected, you need to remove it. Replace it with a plant not susceptible to verticillium wilt.
How to Test for Verticillium Wilt
A sample must be submitted for testing containing vascular discoloration. Look for live wood from the stems or branches with areas of vascular tissue changing from green to brown. You will need to wait between 10 and 14 days for the development of your culture prior to a positive identification of verticillium wilt.