Candidate Seminar- Assistant Professor of Forest Pathology Dr Thomas Shively
November 18, 2025 - November 19, 2025
PSSB A 271 Conference Room
Research Seminar:
“Promoting a pathogen: Verticillium wilt as a biocontrol for tree-of-heaven”
Ailanthus altissima (tree-of-heaven) is one of the most widely distributed and problematic invasive trees across the globe. It is highly susceptible to a vascular wilt pathogen, Verticillium nonalfalfae, and natural infections have been observed in the United States and Europe. A fungal isolate from Pennsylvania, VnAa140, is on petition for approval by USDA APHIS and the EPA as a commercial bioherbicide, but it had not been tested in an expanded range. Inoculations of A. altissima across Virginia with VnAa140 initially showed significant attenuation of the pathogen. After screening for virulence, further inoculations induced much higher levels of disease and mortality in A. altissima, though results varied along environmental gradients. Namely, disease progression was greater at sites with lower average temperatures and cooler microclimates. Host passage was also found to maintain and even restore virulent properties to an isolate, but warm temperatures suppressed both fungal growth in culture and disease symptoms of inoculated seedlings regardless of virulence. Plant communities on inoculated sites that were actively revegetated with native species showed some progress toward restoration goals but were plagued by co-invasions. Finally, preliminary data on host rhizospheric microbiomes suggest that investigation into community changes after inoculation may further inform variability in disease progression. Verticillium nonalfalfae remains a strong candidate for biocontrol of A. altissima, particularly as a part of a wholistic integrated pest management program. Future research will focus on established and emerging pathogens in Michigan, including oak wilt, Heterobasidion root disease, beech leaf disease, and potential bioherbicides for invasive plants.
Extension Seminar
"Where to make the cut: How to manage oak wilt no matter the size of the forest"
Oak wilt, caused by the fungal pathogen Bretziella fagacearum, is one of the most devastating tree diseases in the Midwest. Red oaks can die within weeks of infection, and white oaks may tolerate the disease for years before succumbing. Once a new infection occurs, pathogen spread along interconnected roots can kill many trees throughout a forest stand. In addition to recognizing the symptoms and testing to confirm the presence of the fungus, vigilant monitoring and prevention are key strategies for managing oak wilt on your property. Additionally, recent research has expanded upon established methods for containing infections once they are discovered. While root severing, stump extraction, and salvage harvests are tried-and-true practices to mitigate the impacts of oak wilt, more accessible treatments that involve girdle-herbicide techniques may provide landowners and resource managers greater flexibility in responding to local infections. More research on rapid detection techniques and overland spread involving spore producing trees might further assist with the oak wilt management program.
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