Southern blight of perennial swallowwort (Vincetoxicum spp.) in New York

Authors: PETHYBRIDGE, SARAH - Cornell University; SHARMA, SANDEEP - Cornell University; MURPHY, SEAN - Cornell University; Biazzo, Jeromy; Milbrath, Lindsey

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2021
Publication Date: 11/22/2021
Citation: Pethybridge, S.J., Sharma, S., Murphy, S., Biazzo, J., Milbrath, L.R. 2021. Southern blight of perennial swallowwort (Vincetoxicum spp.) in New York. Invasive Plant Science and Management. 14(4):223–231. https://doi.org/10.1017/inp.2021.30.
DOI: https://doi.org/10.1017/inp.2021.30

Interpretive Summary: The soilborne fungus Athelia rolfsii was discovered reducing an invasive pale swallow-wort population in a county park in upstate New York. The potential to use the fungus for the biological control of invasive pale and black swallow-worts was evaluated. Adult plants of both species were susceptible to infection by A. rolfsii, and survival of the resting body of the fungus (sclerotia) between seasons was demonstrated. This information extended the northern-most range of the fungus which was thought to previously only survive between seasons in sub-tropical and tropical environments. However, studies of infection at the discovery site showed limited spread and highly aggregated diseased plants between years, suggesting that without deliberate and widespread redistribution of the fungus only limited reductions in swallow-wort populations can be achieved. The difficulty in preventing the spread of sclerotia to undesired locations, and the broad host range of the pathogen, including many economically important species (vegetables and field crops), further discounts the feasibility of using A. rolfsii for the biological control of swallow-worts.

Technical Abstract: Pale swallowwort [Vincetoxicum rossicum (Kleopow) Barbar.] and black swallowwort [Vincetoxicum nigrum (L.) Moench] are invasive perennial viny milkweeds that have become prevalent across natural and managed habitats in northeastern North America. Southern blight of V. rossicum caused by the fungus, Athelia rolfsii (Curzi) C. C. Tu & Kimbr., was reported at a New York county park in 2008, resulting in a decline in V. rossicum stands. The disease outbreak and persistence of the pathogen between years highlighted the potential of A. rolfsii for Vincetoxicum spp. control. To better characterize A. rolfsii’s pathogenicity and biology, we studied virulence to adult Vincetoxicum spp., spatial and spatiotemporal attributes of the Southern blight epidemic at the discovery site over four years, and sclerotial survival in New York over two years. Disease incidence and severity were high for both Vincetoxicum spp. in misting chamber experiments. The spatiotemporal spread patterns of Southern blight in V. rossicum suggest the epidemic in the first year of monitoring (2016) was already highly aggregated and that subsequent spread was limited and resulted in significant local aggregation. Sclerotial survival studies at two locations (Pittsford and Ithaca, New York) demonstrated the A. rolfsii isolates can overwinter in upstate New York and are pathogenic to Vincetoxicum spp. the subsequent season. However, shallow burial of sclerotia more rapidly reduced survival compared with placement on the soil surface. Overwinter survival of A. rolfsii sclerotia in New York is notable as this pathogen is typically associated with sub-tropical and tropical regions. Broadcast applications of the pathogen would be needed for widespread Vincetoxicum control at a site, but even restricting releases to select locations would not prevent pathogen movement off-site via water or machinery. The known risks of A. rolfsii to other broadleaf plants in natural and agricultural settings suggest a low feasibility of use for the biological control of Vincetoxicum spp.