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Potential biological control of the invasive Ailanthus altissima (tree-of-heaven) in Virginia using naturally occurring Verticillium wilt fungi

Rachel Brooks: Virginia Tech

<div><em>Ailanthus altissima </em>(tree-of-heaven) is a difficult-to-control invasive tree that is now found in all continents but Antarctica. Research in Pennsylvania, USA has shown that two species of naturally occurring <em>Verticillium </em>wilt fungi may be able to act as biological control agents against this tree. To determine the effectiveness of these fungi outside of Pennsylvania, 24 plots dominated by <em>A. altissima </em>were located throughout Virginia, USA. A randomized complete block design was used to test 4 conidial suspension treatments (<em>V. nonalfalfae</em>, <em>V. dahliae</em>, a 1:1 ratio of both, and water). In total, 524 <em>A. altissima </em>were stem-inoculated in May 2017 using a refined hack-and-squirt method. These plants were monitored at 0, 0.5, 1, 2, and 3 months post inoculation. The area under the disease progress stairs (AUDPS) for each plot was analyzed by treatment type and four representative site covariates (maximum temperature, average stem diameter at breast height, total rainfall, and average stem height). Independent of covariates, AUDPS differed significantly (P<0.05) between treatments, with both <em>V. nonalfalfae</em> and the combination of both fungi producing the highest AUDPS scores. Two covariates, maximum temperature and tree height, showed a significant (P<0.05) negative relationship with the AUDPS score, suggesting that some regional variation may occur. Further monitoring will give insight into how effective these pathogens may be throughout <em>A. altissima</em>’s introduced range.</div>

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