Canadian Forest Service Publications

Wide host-range pathogens as potential bioherbicides – risk analysis. 2000. Bourdôt, G.W.; de Jong, M.D.; Shamoun, S.F. Page 181 in Abstracts of the III International Weed Science Congress, June 6-11, 2000, Foz do Iguassu, Brazil. International Weed Science Society, Corvallis, Oregon.

Year: 2000

Issued by: Pacific Forestry Centre

Catalog ID: 18056

Language: English

Availability: Not available through the CFS (click for more information).

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Host-specificity is a prerequisite for exotic pathogens intended as classical or inoculative biological weed control agents to avoid unintentional effects in non-target species. By contrast, we propose that host specialisation is an unnecessary constraint for pathogens intended as bioherbicides when these pathogens are indigenous or endemic to the region in which their use is proposed. Locally increased inoculum density is a characteristic of the bioherbicide approach to weed control and may result in an additional risk of disease in non-target plants growing beyond the biocontrol site, or in crops planted at the site at some later time. The appropriate measure of this “relative” risk is the ratio of the density of inoculum added due to the deployment of the bioherbicide, to that naturally occurring in the ecosystem of interest. An acceptable value for this ratio must be set that reflects the risk averseness of the decision-makers in government departments, growers and the public at large. Spatial and temporal variation in this ratio for a particular bioherbicide programme may be quantified using models for the escape and dispersal of inoculum created at biocontrol sites, in conjunction with estimates of the density of naturally occurring inoculum of the pathogen. Using such models, risk analyses have been conducted for the plurivorous plant pathogenic fungus Chondrostereum purpureum in The Netherlands and in Canada. These models (along with molecular marker studies in Canada) have enabled the regulatory authorities to sanction and define the conditions for the safe use of C. purpureum for the control of Prunus serotina, Alnus sp., Acer sp., Populus sp. and Salix sp in forestry. In New Zealand, models have also been applied to estimate minimum isolation distances and withholding periods for S. sclerotiorum used as a mycoherbicide to control Cirsium arvense in pastures.