Wilson Bros Gardens LLC

Based on that I recently lost a well-established, prized redbud tree to disease, which was a focal point specimen in my backyard landscape, I felt compelled to write and publish this article.

Redbud trees, Cercis, are very adaptable, hardy and beautiful trees, but as any living thing they are susceptible to disease, especially under certain environmental condition. Though not prevalent, there are two more common diseases redbuds are susceptible to. read on to find out more about these two diseases and steps you can take to possible save infected trees and/or stop the spread to other trees.

Verticillium wilt attacks and kills redbud trees. Verticillium Wilt is a very common disease that attacks a large number of trees. It is caused by a soil-inhabiting fungus called Verticillium. The fungus can enter the tree through the soil but can also be introduced into through a wound and is often spread by pruning equipment that has not been properly sanitized between cuts made. Once in the tree, the fungus begins to spread throughout the tree’s vascular system, as the fungus level increases the tree’s vascular system becomes blocked preventing the tree from adequately moving water and nutrients throughout the tree.

Internal streaking in the sap wood is an indicator of verticillium wilt

The first external signs that a tree has a Verticillium Wilt infection is the yellowing and then browning of leaves at the ends of some branches. Initially the yellowing and browning of the leaves is spotty throughout the tree and does not follow a uniform pattern. As the fungus begins to block the vascular system, the browning of leaves becomes more acute and more wide-spread. New leaves generally are either non-existent, undersized or yellowed.

As the disease spreads, the infected tree may slowly die, branch by branch over several seasons. The symptoms and severity of Verticillium wilt are much more harsh during droughts.

Unfortunately, there is no chemical control for Verticillium Wilt however there are several steps that can be undertaken to help control the spread of the disease, as well as enhance a tree’s ability to control or even contain the disease. These include pruning, fertilizing and watering.

Prune and remove all dead wood. The pruning should be a few inches below the diseased area, so as to remove as much of the fungal concentrations as possible. When pruning do not remove branches that have recently wilted as they may reflush again in a few weeks or the following spring. When pruning be sure to properly sanitize the pruning tools with a solution after each cut. Pruning blades can be sanitized by dipping them in a solution of 1 part bleach to 9 parts water.

In spring or summer, give the tree a very good fertilization with a slow release tree and shrub fertilizer containing nitrogen. 

In the absence of rainfall during the warm season, it is important to give a Redbud tree suffering from verticillium wilt a deep root watering at least twice or three times a week. The objective of a deep root watering is to ensure that the water penetrates deep into the soil, to a depth of at least 24 to 36 inches so that the entire root zone is hydrated. The easiest way to give a large tree a deep root watering is to place either a sprinkler or a soaker hose over the tree's drip line (around the perimeter of the canopy) and let it run for about 2 hours, ensuring lots of water penetrates the soil. 

The other disease that could be present is dieback/canker, which is the most destructive disease that attacks Redbud trees. It is first seen as a tree’s leaves wilt and turn brown. Often cankers can be seen on branches and twigs. The cankers can either be seen as visible cankers on the surface of the branches or as dark sunken areas with black centers.

The canker or dieback is caused by a fungus (Botryosphaeria ribis) which attacks not only the redbud but more than fifty other types of trees and shrubs. The disease is spread throughout the tree, or from tree to tree, by splashing rain and winds that move the fungus from diseased areas to healthy parts of the tree. The fungus then enters the tree through wounds or dying branches. The fungus gradually spreads out within the tree’s vascular system slowly blocking the tree’s vascular system and inhibiting its ability to transport nutrients and water. The result is a gradual dieback of branches as the flow of nutrients and water is cut off.

There is no effective chemical control for the canker. If canker is identified in a tree, prune out and destroy dead branches and infested areas. Be sure to make pruning cuts at least 3 or 4 inches below the canker, so that the cut is into healthy viable wood. After every pruning cut, be sure to properly sanitize the pruning tools so that the fungus is not transferred to healthy parts of the tree.

If your redbud tree doesn't make it, and/or you decide to replace it, I would suggest not going with another redbud. Reason being, if it's verticillium wilt or dieback canker the new tree might become infected. Instead, I'd go with different tree species resistant to these diseases. Dogwood trees and crape myrtle trees are two good alternatives that come to mind. Regarding dowgoods, the Chinese species and varieties (Cornus kousa) are the most resistant to all types of diseases. 

Some other trees that are resistant to verticillium wilt:

Hope this information was helpful to you.

Plant Long & Prosper!