Predictability of pathogen host range in classical biological control of weeds: an update

Abstract

Before an exotic pathogen can be released as a classical biological control agent the likely positive and negative outcomes of that introduction must be predicted. Host range testing is used to assess potential damage to non-target plants. To-date 28 species of fungi have been released as classical biological control agents against weeds world-wide. These pathogens have been reported infecting only six non-target plant species outdoors and all of these incidents were predicted. Many more non-target plant species developed disease symptoms in glasshouse tests than in the field. Consequently, data from other sources are needed to ensure potential agents are not prematurely rejected. Predictions of pathogen host range to date have been sufficiently accurate to prevent unpleasant surprises. Exotic pathogens are a safe and useful tool for weed control, especially in natural areas rich in valued non-target species.

Risk assessment of the Acacia cyclops dieback pathogen, Pseudolagarobasidium acaciicola, as a mycoherbicide in South African strandveld and limestone fynbos

“…This lack of susceptibility in the field could be ascribed to the hardiness and slower growth of plants in the field compared to the nursery. Therefore findings of this study, in support of Barton (2012),…”

“…Of the 28 fungal biological control pathogens released internationally and reviewed by Barton (2012), 107 plant species were found to be susceptible in glasshouse pathogenicity trials prior to release. However, only six of these species were actually found to be affected in the field post-release.…”

Biodiversity-based options for arable weed management. A review

“…Notably, this involves ascertaining the host spectra, so as not to affect the crops and to measure the impact of inundative inoculation of a strain or set of fungal strains on the wider environment. It can be derived from field observations but also by using of predictive models designed to assess the risk of misuse of a pathogen to control a weed (Barton 2012;Berner and Bruckart 2012). This evaluation should also focus on estimating the cost/benefit ratio of biocontrol versus chemical and/or mechanical approaches.…”

Mimosa pigra dieback in the Northern Territory, Australia: Investigation into possible causes

“…Mass production of potential biocontrol agents, formulation, shelf-life, optimum inoculum concentration, adequate conditions for fungus effectiveness against the weed and host range, require a series of studies for the successful adoption of this approach (Upadhyay et al 2011;Barton 2012). …”