Verticillium Wilt and the Redbud

See the dark rings in the heartwood?

Today we cut down an old Redbud tree that leafed out poorly this spring. The tree has been suffering for years with a pathogen called Verticillium wilt. The crosscut of the tree shows the bark around the edge, then the white sapwood, then the darker heartwood. Heartwood consists of sapwood cells that have died which is natural. Within the sapwood there are rings that are occasionally much darker than the dark heartwood. These near black streaks in the vascular tissue of the tree are where the pathogen Verticillium tried to plug up the tree. The tree grew around them many times in its life. Old age and pathogens plus a nice canker rotting the trunk overcame its defenses.

Stump of a Redbud Tree

Here is a picture of how small the leaves were this spring. The flowers bloomed but the leaves were not getting enough water through the vascular system to push out the leaf buds and develop normal leaves.

Small leaves are a symptom of vascular disease

Verticillium wilt is a fungal disease carried in the soil. Many many species of plants are susceptible to it. For a complete list, check a pathology book or ask in the comments. There are about a hundred susceptible species. When the fungus in the soil comes into contact with feeder roots, the fungus enters. The fungus grows and proliferates eventually making reproductive spores. Spores are carried around the whole plant by the water going up the stem. As the fungus spreads systemically, its main function is to block the vascular tissue. It can also create trunk cankers. Here is a picture of trunk damage.

This trunk was very rotten from a canker

Just an aside about the spring flowers it had this year. The flowers were not very affected. The buds were already formed last summer. The buds just needed a little water to flow into them this spring to telescope out the cells and form flowers. Just because your tree flowers, it does not mean that it is healthy. In fact, many times, the biggest burst of flowers come just before a tree dies. The tree wants to make as many babies (seeds) as it can to continue its species in the world. SO flowering heavily may be a sign that your tree is checking out.

There is no remedy for Verticillium wilt. Try to buy healthy looking nursery stock from cultivated fields. Once a tree has died in the soil from Verticillium
wilt, the soil will be contaminated with the fungus. Be sure to replant a resistant species or plant far away from that spot. The spores will last in that soil longer than your lifetime. I will be replanting an evergreen of some type.

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1 Comment

  1. Kevin said,

    June 2, 2010 at 12:59 PM

    You should write a post about painting white around the bases of trees. I’ve heard/read things about minimizing sun/heat, it being an insectiside, and it being lime (neutralizing acidic soil?). Many trees here have white bases like that and I’m curious. Also, some trees we’ve seen are patched with cement in places where branches have been cut off or have split off. Is that a good idea? maybe short term?


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