A naturally occurring fungus might help curb the spread of tree-of-heaven, an invasive tree species that is threatening forests in most of the United States.
When researchers injected the fungus—Verticillium nonalfalfae—into tree-of-heaven (Ailanthus) plots, the treatment completely eradicated the plants from those forests.
“It appears that this treatment is effective in Pennsylvania and could be used as a biocontrol agent throughout the United States,” says Matthew Kasson, who recently received his doctorate in plant pathology and environmental microbiology from Penn State.
Since tree-of-heaven’s introduction into Pennsylvania in the 1780s, the tree has spread from a rare and prized plant for collectors to a nuisance in at least 40 of the 48 contiguous states, Kasson says.
“Trying to find the best way to get rid of tree-of-heaven has become a serious land-management issue. Fire doesn’t seem to work and chemicals and mechanical means are expensive and ineffective, too.”
Using a hatchet that is designed to pump fungal spores into the trees, the researchers tested the fungus on 14 tree-of-heaven stands in south-central Pennsylvania. Usually, it takes three blows of the hatchet to deposit the entire inoculation of about 30 million spores for each tree. The inoculation kills the entire tree, including the sprouts.
Fungus-Carry Beetles
“It’s important that the sprouts are killed, too, because, tree-of-heaven has an extensive system of sprouts that spread just above the ground surface, which is one of the reasons the tree is so difficult to manage,” Kasson says. “The sprouts can immediately grow even if the top canopy of trees dies.”
In 2003, researchers noticed a large number of tree-of-heaven deaths in a southwestern Pennsylvania forest. Large-scale wilt was affecting the trees.
“There were hundreds if not thousands of dying and dead tree-of-heaven in the area, which is very unusual, because tree-of-heaven is very hard to kill,” says Don Davis, professor of plant pathology.
A number of Ambrosia beetles were near the infected stands, leading foresters to theorize that the fungus, often carried through the forests by beetles, was involved in the tree deaths.
Safe for Other Plants
“The Ambrosia beetles may explain some of the long-range spread of the disease,” Davis says. “One theory is that the beetles feed on an infected tree and then take those spores to another healthy tree, which could be miles away.”
The effect that the fungus has on other plants will be the subject of further research, Kasson says. However, preliminary studies on the vegetation that surrounds Ailanthus groves indicate the fungus may not harm nearby plants and trees. Only a small percentage of plants near the infected tree-of-heaven plots showed signs of being harmed by the fungus.
“There are still tests and studies that need to be done in the future to make sure it’s completely safe,” Kasson says. “As a researcher, you can’t be sure until the results of all of those tests are in, but, at this point, I am cautiously optimistic.”
The US Department of Agriculture and Pennsylvania Department of Conservation and Natural Resources supported the work.
Source: Penn State
