Exploiting exotic pathogens as mycoherbicides against invasive alien weeds: Japanese knotweed as a case study

Abstract

Plant species have been introduced increasingly into non‐native ranges, where many have become exotic weeds with adverse impacts on native ecosystems, as well as on farming and other livelihoods. In biological control, the classical or inoculative approach is the one most commonly used for the management of invasive alien weeds and is based on the use of co‐evolved natural enemies from the native range to control the invasive weed. Typically, the inundative or mycoherbicide approach targets problematic weeds using local plant pathogens that, in the case of introduced species, have ‘jumped’ onto the exotic host. The leaf‐spot fungus, Mycosphaerella polygoni‐cuspidati, co‐evolved with its host, Reynoutria (Fallopia) japonica (Japanese knotweed), in Japan and has a unique history of being investigated both as a classical biological control agent and a mycoherbicide against this highly invasive weed in the United Kingdom and North America. Here, we highlight our research on M. polygoni‐cuspidati as part of a biological control programme for Japanese knotweed and review the potential of mycoherbicides using exotic pathogens for the management of invasive alien weeds. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The future of microbial bioherbicides

“…Sixteen of the articles in this issue are from conference participants. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Four related articles from non-participants are also included. [18][19][20][21] The article by Duke gives the rationale for the meeting, discussing the many microbial bioherbicides that have failed and detailing the technical and economic reasons for lack of success.…”

“…The meeting was organized into twenty‐two 50‐min presentations with ample time for discussion. Sixteen of the articles in this issue are from conference participants 2–17 . Four related articles from non‐participants are also included 18–21 .…”

“…Kurose et al . reviews the use of exotic fungal plant pathogens against the invasive weed, Japanese knotweed ( Reynoutria japonica ), in the UK 14 …”

“…Kurose et al reviews the use of exotic fungal plant pathogens against the invasive weed, Japanese knotweed (Reynoutria japonica), in the UK. 14 A perspective on the use and safety considerations involved in broad host-range pathogens and mixtures of more than one weed-specific pathogen as microbial bioherbicides is provided by Bourdôt and Casonato. 15 The topic of accidental introductions of biological weed control agents and what such incidents can teach us are discussed in a perspective.…”

Why are there no widely successful microbial bioherbicides for weed management in crops?

“…For most crops, the microbial bioherbicide must be applied in an inundative fashion, like a chemical herbicide, with less reliance on epidemiological spread of the microbe on which the inoculative approach to classical biocontrol relies. Microbial bioherbicides used in the inoculative approach are generally not commercial products, but are usually developed and used by government agencies such as those that funded the work of Kurose et al 9 for the development of Mycosphaerella polygoni-cuspidati of Japanese knotweed (Reynoutria japonica). There is a commercial bioherbicide product for use against an invasive species (Di-Bak®) (Table 1), but it does not follow the classical inoculative approach.…”