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Abstract
Ailanthus altissima (Mill.) Swingle commonly known as tree-of-heaven is an invasive tree species that has spread through much of the USA. Significant mortality of A. altissima by a highly host-specific strain of the fungus, Verticillium nonalfalfae Inderb. (formerly Verticillium albo-atrum Reinke and Bethold), has been recently documented in Pennsylvania. To detect the regional distribution of this biological control agent in the Southeast, a windshield survey was conducted in Virginia, North Carolina and South Carolina to locate V. nonalfalfae-infected A. altissima stands. The survey covered 26,500 km of interstate highways and primary and secondary roads. There were 90 potential sites located throughout the three states. Of those, six were found to be infested with the fungus, all in the mountain regions of Virginia. Inoculation tests suggest no difference in virulence among the six V. nonalfalfae isolates on A. altissima, which resulted in 100% mortality in 9–11 weeks post-inoculation. Tree ratings revealed differences in health among sites, but all sites had an increase in disease incidence from 2011 to 2012 (mean = 4.7 ± 3.8%), suggesting this fungus is dispersing. This survey provides evidence that biological control using this fungus may be possible in Virginia.
Acknowledgements
We would like to thank Jackie Brown, Molly Darr, Natalie Morris, Carrie Jubb, Tom McAvoy, Ryan Mays and Katlin Mooneyham for their survey assistance. We would also like to thank Dr. Chris Asaro, Rob Trickle and Laurie Reed for A. altissima location information, and Dr. Matt Kasson for the molecular identification of the isolates.
Funding
This research was supported by the US Department of Agriculture, Forest Service [10-DG-11083150-004].