Towards ecologically based baiting strategies for rodents in agricultural systems

Abstract

Rodents are a major pest in Australian agricultural systems where they periodically irrupt (outbreak) and cause serious damage to crops. These irruptions still occur despite extensive baiting campaigns. Most of the economic losses caused by rodents occur in cereal and oilseed crops, although significant damage occurs annually in both sugar cane and macadamia orchards. Currently, attempts to control rodent outbreaks rely heavily upon baiting with rodenticides. As these are normally applied in an emergency situation and without adequate scientific insight or planning, they are usually not cost effective. We present strategies aimed at reducing agricultural losses in the event of an outbreak that take into consideration important population processes such as: (a) the stage of development of the rodent population; (b) the likely course of population trends given prevailing environmental conditions; (c) the spatial relationship between the available habitat types; (d) the role of refuge areas in seeding adjacent areas and sustaining a high population in the absence of a crop habitat type; (e) the likely dispersal strategy of the population given the landscape of the area; (f) the consequences of dispersal into areas that do not yet sustain a high population, and for crops that will be harvested late in the season. A process, presented in the form of a flow diagram, has been developed to tailor rodent control programs to specific outbreak conditions. Initially, the extent of a reported rodent problem and the scope of a control program are determined. Where a control program is required, this is developed for each region individually and is based on results of extensive population and crop surveys. Bait application rates are specifically determined for each rodent outbreak, reducing the probability of under- or over-baiting. Two baiting strategies have been developed for inclusion into the control program, a protection strategy and a control strategy. The former is designed to frustrate responsive dispersal into crops at harvest, whilst the latter will reduce numbers and maintain them at a low level until harvest. The procedure is reiterated for as long as the problem persists allowing control procedures to be modified as population and crop changes occur. Using Australian examples to illustrate the ecological concepts underpinning rodent management in an emergency situation, the control processes outlined will have universal application in the management of rodent outbreaks in agricultural systems.