Evaluating the feasibility of eradication for terrestrial weed incursions
F.D. Panetta1 and Susan M. Timmins2
1 Alan Fletcher Research Station, Department of Natural Resources and Mines, and CRC for Australian Weed Management, PO Box 36, Sherwood, Queensland 4075, Australia.
2 Science and Research, Department of Conservation, PO Box 10-420, Wellington, New Zealand.
The feasibility of eradication of weeds has had little systematic investigation, in contrast to eradication feasibility for pest animals. A fundamental condition for realising the objective of eradication is that the rate of weed removal exceeds the rate of weed increase at all population densities. If this is not so, the eradication program may be prolonged or even fail. We present a decision tree that can be used to determine whether eradication is an appropriate management strategy for a weed incursion. We also investigate various factors in terms of their ability to impede progress towards eradication, and offer a prospective scoring system that captures the influence of logistic, detection, biological and control factors upon the effort required to achieve eradication.
A recent analysis of selected weed projects indicates that eradication feasibility declines rapidly with increasing area of a weed infestation, to the point where eradication is unlikely for infestations of greater than 1000 ha. This generalization is based upon 'gross' infestation size (i.e. the area that must be surveyed in return trips following control treatments), as opposed to 'net' infestation size (the area to which treatment is applied). For species that are readily detectable and combine long pre-reproductive periods with limited seed persistence, it may be possible to eradicate infestations larger than 1000 ha. Certain combinations of weed characteristics and environmental contexts may restrict eradication potential, however. The scope for eradication of some weeds of natural ecosystems may be limited to infestations that are considerably smaller (perhaps by an order of magnitude) than 1000 ha. More examples of successful eradication programs are required in order to develop further our scoring system, particularly as it would apply to weeds of natural ecosystems. Even when eradication is technically possible, it appears that relatively long-term financial and institutional commitment will generally be required for success.
Plant Protection Quarterly (2004) 19 (1) 5-11.