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Forest Disturbance Processes

Ailanthus and Verticillium nonalfalfae

[photo:] Treating Ailanthus trees with biocontrol fungus - an aqueous solution of fungal spores is squirted into three wounds created by a hatchet at the base of each tree. Photo by Joanne Rebbeck, US Forest Service northern Research Station.Research Issue

Ailanthus (Ailanthus altissima), also called tree-of-heaven, has been in North America for more than 200 years. In the last 60 years, it has begun moving out of roadsides, big cities and small towns and into rural forests. Ailanthus has the potential to replace oak and other native tree species, thus dramatically affecting native food sources for numerous wildlife species.

Ailanthus is uniquely equipped to supplant native trees and other vegetation:

  • Sapling growth can reach 3-4 feet in one year; out growing nearly any native tree species. Mature trees can reach 80 feet in height.
  • Ailanthus has male and female flowers on separate trees.
  • Typically, trees are producing seeds after 3-5 years.
  • One female tree can produce up to 350,000 seeds per year. These highly conspicuous papery seed clusters persist throughout the winter. Seeds are easily distributed by wind, compared with oak acorns which are dependent upon wildlife for dispersal.
  • Ailanthus is allelopathic. It produces chemicals that influence the growth, survival, and reproduction of other plants.

Our Research

At several sites in Ohio, including the Wayne National Forest, state forests, and one forest managed by a non-government organization, the Forest Service’s Northern Research is beginning a field trial of a native fungus as a means of killing Ailanthus trees that is cost-effective and does not use chemicals.

Research in Pennsylvania and other states has demonstrated that a native fungus, Verticillium nonalfalfae (Vn), is a fast-killing pathogen.  The particular variety used in this test specifically targets Ailanthus. This field trial will help assess the potential value of Vn as a non-chemical, sustainable means of controlling Ailanthus, which could help restore healthy native forests.

To date more than 71 species of trees and shrubs have been tested for sensitivity to the fungus and only a handful has shown sensitivity. These include devils walkingstick, striped maple, and sumac. Rates of infection are very low, however. Joanne Rebbeck, a plant physiologist stationed in Delaware, Ohio is working to expand testing of other native plant species as well as agricultural crops.

At each of the five study sites across Ohio, the fungus will be introduced on four plots while one plot will not be treated with Vn to serve as control. A total of 40 Ailanthus trees will be treated at each study site.  Every plot at every study site will be monitored biweekly to evaluate symptom development of the inoculated trees and spread to non-treated Ailanthus trees.  In addition, the health and condition of all other tree, shrub, and herbaceous plants will be evaluated for possible non-target impacts.

Preliminary trials in summer 2014 have been successful at the Tar Hollow and Vinton Furnace State Forests, and no off-target effects have been observed.

Expected Outcomes

From this field trial, scientists and managers will learn how the native forest responds to the removal of Ailanthus. The field test will also increase our understanding of how effectively Vn spreads beyond the initial application site. Based on the population of the Ailanthus being treated, it is estimated the fungus could spread 200 to 400 feet per year via root transport. Rate of spread could be much less in areas where Ailanthus density is low.

The lessons learned in this field trial may eventually lead to an effective management tool for forest managers dealing with Ailanthus infestations.

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Last Modified: January 3, 2017