Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2011
Publication Date: 3/1/2012
Citation: Gibson, D.M., Castrillo, L.A., Donzelli, B.G., Milbrath, L.R. 2012. First report of blight caused by Sclerotium rolfsii on the invasive exotic weed, Vincetoxicum rossicum (pale swallow-wort) in western New York. Plant Disease. 96:456. Interpretive Summary: Two emerging invasive plant species in the northeastern United States and southeastern Canada are pale swallow-wort and black swallow-wort. Based on an observation of a declining natural population, we identified a fungus capable of causing extensive mortality in both swallow-wort species. Although we do not yet know the potential utility of this fungus for weed control, this isolate may offer potential as a bio-herbicide for invasive swallow-worts in natural ecosystems if it can be demonstrated that this isolate has a restricted host range and could be approved for environmental releases.
Technical Abstract: Pale (Vincetoxicum rossicum) and black swallow-wort (V. nigrum) are invasive, perennial twining vines that are becoming increasingly problematic in the northeastern U.S. and southeastern Canada. Observations at one natural area heavily populated by pale swallow-wort in Monroe County, NY, revealed a gradual decline of pale swallow-wort with restoration of native grasses and some dicot species. Affected plants showed extensive yellowing and wilting of foliage, with white mycelium throughout the stem and crown area; small reddish brown sclerotia were evident. The fungus was identified as S. rolfsii; since the fungus was found in the northern US, we suspected that this isolate might be S. rolfsii var. delphinii due to the reported inability of S. rolfsii to persist in low temperature extremes. Sequences of 18S gene, internal transcribed spacer regions, and 28S gene of the ribosomal DNA identified the isolate, VrNY, as S. rolfsii. Pathogenicity tests were conducted by inoculating 2 month old seedlings of V. rossicum and V. nigrum. Characteristic symptoms developed over a 28 day period, with most plants showing disease within two weeks, while all control plants were symptomless. Mortality in treated plants reached 66% and 60% with V. rossicum and V. nigrum, respectively. Since the spread of this fungus is limited by the presence of soil-borne sclerotia (as a non-spore producer), this isolate may offer potential as a bio-herbicide for control of invasive swallow-worts in natural ecosystems if it can be demonstrated that this isolate has a restricted host range.