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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #425127
Research Project: Discovery and Development of Microbial-Based Biological Control Agents for Use Against Invasive Weeds in the United States

Location: Foreign Disease-Weed Science Research

Title: A foliar disease of invasive black swallow-wort (Vincetoxicum nigrum) caused by Boeremia exigua

Author
item Fulcher, Michael
item FITZ, RILEY - Oak Ridge Institute For Science And Education (ORISE)
item JOHNSON, ALEXANDRA - University Of Rhode Island
item TEWKSBURY, LISA - University Of Rhode Island
item Tancos, Matthew

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2025
Publication Date: 4/16/2026
Citation: Fulcher, M.R., Fitz, R., Johnson, A., Tewksbury, L., Tancos, M.A. 2026. A foliar disease of invasive black swallow-wort (Vincetoxicum nigrum) caused by Boeremia exigua. Plant Disease. https://doi.org/10.1094/PDIS-03-25-0684-SC.
DOI: https://doi.org/10.1094/PDIS-03-25-0684-SC

Interpretive Summary: Pathogens from invasive weeds are rarely studied, but their characterization is essential for developing biological control agents, uncovering new risks to crop production, and improving plant disease diagnostics. In collaboration with the University of Rhode Island, ARS scientists in Maryland discovered a previously unidentified fungal disease affecting black swallow-wort, an invasive vine that damages crops and livestock throughout the northeastern United States. Although the pathogen causes only minor damage to the vine and poses little risk to cultivated plants, it holds unique genetic diversity that challenges existing diagnostic methods. These findings will help plant pathologists refine detection tools and investigate potential weed controlling compounds made by the fungus.

Technical Abstract: Black swallow-wort (Vincetoxicum nigrum) is an aggressive invasive vine infesting pastures and fields in the northeastern United States. An unknown fungal pathogen was recovered from foliar lesions occurring on black swallow-wort at two locations in Rhode Island in 2022 and was identified as Boeremia exigua based on cultural, morphological, and molecular descriptions of eight isolates. A single isolate, FDWSRU 22-216, was evaluated for pathogenicity on black swallow-wort to assess potential weed biological control value. Minor disease symptoms reproduced under controlled conditions did not appear to substantially reduce the health of infected black swallow-wort. Since broad host range pathogen species found on weeds may pose a disease threat to crops, cultivated plants including tomato, barley, sunflower, and flax were evaluated for susceptibility to the pathogen. None of these crops developed disease symptoms following inoculation with B. exigua, suggesting that the pathogen population associated with black swallow-wort poses little direct risk to crop production. However, using taxon-specific markers, two B. exigua genotypes, including one that does not correspond to existing reference material, were described. The dominant genotype was capable of higher growth rates in vitro at 30°C, suggesting potential phenotypic differentiation between genotypes. This study reports the first instance of B. exigua on a black swallow-wort species and highlights the potential for widespread invasive plants to harbor previously undescribed pathogen diversity.