Verticillium Wilt

Verticillium wilt (also maple wilt) is a vascular disease caused by two species of fungi, Verticillium albo-atrum and Verticillium dahlia.  As a vascular wilt disease (similar to oak wilt or Dutch elm disease), verticillium fungi live in the sapwood of infected trees, reducing the tree’s ability to move water and nutrients up to its leaves.  This disease progresses differently in each affected species of tree, often lingering for years before a secondary insect or disease finally kills the tree.  Verticillium wilt can survive in the soil for up to 15 years, often causing a problem when susceptible trees are planted where the soil is already infected.

Treatment Strategy

Unfortunately, there is no known treatment for verticillium wilt.  Good cultural practices, including watering, mulching, and low-nitrogen fertilization provide infected trees with the resources required to extend their survival.  Trees with recent symptoms do not need to be removed immediately as they may recover.  If your tree does succumb or begins to look so unsightly that removal is your preference, be sure to replace it with a resistant tree or shrub.  Contact a Tree Geek for a list of trees and shrubs that are resistant to verticulum/maple wilt in your area.

Watering

Adequate water is a key factor in maintaining healthy trees.  A slow, deep watering event once every few weeks during dry conditions helps maintain soil moisture levels and minimizes the stress that allows verticillium wilt to cause significant damage.

Mulching

Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy, fibrous roots.

How Is It Spread?

Biology

The verticillium fungus moves into the tree via its roots or open wounds on the lower trunk.  Once in the tree, the fungus multiplies rapidly, causing the tree to attempt to block its growth.  This attempt to block fungal growth also blocks the tree’s conductive tissues, depleting its leaves of water.  Although plugging up conductive tissues can cause wilting and dieback in the canopy, the tree’s response to the verticillium  fungi is slower than that of other vascular wilt diseases.  Wilted portions of a tree may return to health in subsequent years.

Susceptible Trees

Verticillium wilt affects over 300 species of trees, some of which include ash, elm, catalpa, magnolia and maple.  Maple trees are by far the most susceptible, which is why this fungus is often called maple wilt.

Symptoms

  • Small yellow leaves
  • Leaf scorch
  • Slow growth with heavy seed crops
  • Early fall color
  • Branch dieback
  • Green to brown streaking in the sapwood of infected branches

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