Development and application of the fungal plant pathogen Colletotrichum shisoi to control invasive Perilla frutescens

Inadvertently introduced plant pathogens that infect invasive plant species might 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 biological control activity. Under controlled conditions, application of the pathogen reduced perilla biomass, flower production, and interspecific competitive ability. In a replicated field trial, both the introduction and 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.