Has Tree-of-Heaven Met Its Match?

excerpted from “Branching Out”, University of Maryland Extension Aaron Cook & Lee Reich

A naturally occurring fungus might help curb the spread of an invasive tree species that is threatening forests in most of the United States, according to researchers at Penn State, Virginia Tech, and West Virginia University.

Researchers tested the fungus, Verticillium nonalfalfae, by injecting it into tree-of-heaven, or Ailanthus, plots. The treatment completely eradicated the tree-of-heaven plants in those forests.

“It appears that this treatment is effective in Pennsylvania and could be used as a bio-control agent throughout the United States,” said Matt Kasson, a former Doctoral Candidate at Penn State University.

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.

One of the problems is that if you cut it down, it won’t go away. New sprouts enthusiastically pop up from the cut stump, even after years of recutting. What’s more, the spreading roots send up sprouts that eventually can grow  into full size trees at some distance from the mother plants. “Full size” for tree-of-heaven means 40 to 60 feet or more.

Although a single tree-of-heaven lives rarely more than 50 years, those roots sprouts stand ready and waiting to replace any old top growth in decline.

Additionally, tree – of – heaven also is among the fastest – growing trees. At 3 to 5 feet per year, it can quickly outstrip competitors, whether they are cultivated plants or weeds. It also tolerates adversity. This is “a tree that grows in Brooklyn,” thriving despite heat, cold, alkaline or acidic soil, wet or dry soil, even infertile soil and polluted air.

Further complicating matters are its seeds. Each tree can potentially cast more than 300,000 seeds to the wind.

Each seed has wings that ensure it doesn’t drop to the ground before first hitchhiking a ride on the slightest breeze.

Trying to find the best way to get rid of tree-of-heaven has become a serious land management issue; it can cost up to $3,500 an acre to eradicate the invasive tree.

Dr. Donald Davis, professor of plant pathology at Penn State University, said that in 2003, he noticed a large number of tree-of-heaven deaths in a southwestern Pennsylvania forest.  The foresters in the area then took him to a site where large-scale wilt was affecting the trees. Davis described 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.

The researchers also noticed a number of Ambrosia beetles near the infected stands, leading them to theorize that the fungus, often carried through the forests by beetles, was involved in the tree deaths. The Ambrosia beetles may explain some of the long-range spread of the disease; 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.

Studies on the vegetation that surrounds Ailanthus groves indicate the fungus does 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, specifically devil’s walking stick and striped maple…