Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2024
Publication Date: 6/1/2024
Citation: Fulcher, M.R., Little, R.R. 2024. Development and application of the fungal plant pathogen Colletotrichum shisoi to control invasive Perilla frutescens. Biological Control. 194:105543. https://doi.org/10.1016/j.biocontrol.2024.105543.
DOI: https://doi.org/10.1016/j.biocontrol.2024.105543

Interpretive Summary: Invasive perilla mint disrupts native plant communities and poses a toxicity risk to grazing livestock. Developing a biological control agent for this weed would provide a new option for management in organic systems or environments sensitive to chemical and mechanical disruptions. In this study, a naturally occurring fungal plant pathogen was found to control perilla growth in laboratory and field experiments conducted in Maryland. Application of the pathogen severely limited perilla growth and reproduction while having small but positive impacts on plant diversity in forest plots. Researchers found a cost-effective method for producing the pathogen and identified challenges to the preservation and transport of the fungus. This work supports scientists and land managers who could redistribute the fungus across perilla’s invasive range.

Technical Abstract: Inadvertently introduced plant pathogens may be effective weed biological control agents if developed for redistribution or augmentation of naturally occurring populations. Colletotrichum shisoi is likely an inadvertent introduction to the United States where it causes disease on invasive perilla mint (Perilla frutescens). This study reports on the development and application of C. shisoi as a biological control agent. The effects of dew period on infection probability and of inoculum concentration on perilla biomass production were determined to identify a threshold dose and dew period required for effective biocontrol activity. Under controlled conditions, application of the pathogen reduced perilla biomass, flower production, and inter-specific competitive ability. In a replicated field trial, the introduction or augmentation of C. shisoi populations caused high perilla mortality and moderate changes in plant community composition over one growing season. Additionally, a series of experiments were performed to evaluate methods for the production and preservation of C. shisoi spores. Overall, the pathogen was found to be an effective antagonist of perilla mint when applied inundatively under appropriate conditions. It may be possible to produce the pathogen in mass for redistribution across the invaded range of perilla in North America, but further research is needed for adequate preservation of inoculum during transport and application.