New potential biocontrol on invasive Tree-of-Heaven

Tree-of-heaven (Ailanthus altissima), an invasive tree in North America

Tree-of-Heaven (Ailanthus altissima) is an invasive tree in much of North America that was introduced from China (not Heaven, as the name might imply) as a garden ornamental in the late 1700’s (see North American geographic range here).  This tree is particularly difficult to get rid of, because a single tree can make up to 325,000 seeds in a year, can easily grow 6 feet in a year, and can spread, even if reproduction through seed is inhibited or the tree is cut down, through vegetative sprouting.  Currently, the best control measures are chemical.

Biocontrols are biological phenomena (such as disease and predators) that are used to combat unwanted non-natives.  Biologists are currently exploring potential biocontrols for Ailanthus, and a disease called Verticillium albo-atrum was recently discovered that might hold promise.  Mark Schall and Donald Davis at Pennsylvania State University noticed a stand of tree-of-heaven dying in southern Pennsylvania, and molecularly identified the pathogenic cause to be V. albo-atrum.  Symptoms of the disease include yellowing, browning, and wilting of leaves or branches, in severe cases resulting in leaf loss and potential death.  The disease spreads through wind-borne spores, and, after infection, the fungus invades the cells that transport water, dehydrating the plant. 

Verticillium spore-bearing structures

Verticillium fungi are known to infect and cause leaf wilt and sometimes death in more than 200 plant species, including common trees and crop plants.  Verticillium wilt is common in landscape trees, but uncommon in North American forests.  A potential biocontrol cannot pose risk to other species in order to be legal.  In initial studies inoculating trees that associate with tree-of-heaven, Schall and Davis report that  V. albo-atrum caused severe disease in tree-of-heaven only, with the possible exception of striped maple. The strain of this disease that is infecting Ailanthus remains promising as a potential biocontrol, but the risk it poses to other forest species remains questionable.  Few diseases that specialize on a particular tree alone cause complete host eradication (because then they would eradicate themselves), so even if Verticillium is a successful biocontrol, other control measures will need to be used with it in order to exterminate the invasive tree.


New potential biocontrol on invasive Tree-of-Heaven — 2 Comments

  1. I believe that I have 2 male Tree of Heaven in my back yard. I don’t get any blossoms or fruit from these trees but I do get the little shoots that I pull up all the time. I have noticed at the base of one of the trees, there seems to have been an insect or bird pecked a hole, and the wood is mushy and very wet. Could this be a fungus? The trees don’t really bother me and I have a wonderful large maple tree growing in the yard also. If this is a fungus or some kind of infection, should I have a specialist take samples first before considering cutting down the tree? Thank you for your time and consideration in this matter.

    • I can’t know without seeing it. I suggest taking photos and asking your local extension agent. If a sample will be helpful, they can tell you so and give you directions on what to do next.

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