Efficacy of brodifacoum to control house mice, Mus domesticus, in wheat crops in Southern Australia

Abstract

A field trial to test the efficacy of brodifacoum pellets against house mice ( Mus domesticus) inhabiting wheat crops in the Victorian Wimmera was conducted in spring 1996. The density of mice in wheat crops was approximately 50 mice per hectare. There were two treatments (1 kg ha −1 and 2 kg ha −1) applied aerially using pellets (10 mm in length) with 0.005% brodifacoum. We examined three population indices, minimum number known to be alive, adjusted trap success and population density using the Petersen estimate. In two out of three plots, 1 kg ha −1 was equally as effective as 2 kg ha −1, but in a third it failed for no apparent reason. There were significant reductions in these population indices by up to 99% 7 days after treatment. An application rate of 1 kg ha −1 of brodifacoum is sufficient for effective control of mice in wheat crops which are at maximum tillering and when densities of mice are < 80 ha −1. There was substantial bait unconsumed after 3 days which suggests that a reduced application rate could have sufficed. Nineteen mice were fitted with radio-collars prior to baiting to monitor their fate and location of death at one site treated at 2 kg ha −1. Three disappeared without trace. Of the remainder, 25% ( n = 4) were located dead on the surface or half submerged in burrows and 75% ( n = 12) died underground. All mice died at least 3 days after baiting. Mice were observed on the surface during the day indicating that ingestion of brodifacoum may have changed their behaviour, especially their activity patterns. This may increase the risk of predation and hence the risk of secondary poisoning. No bodies of non-target species were found in the treated crops up to 9 days after application of brodifacoum.