Evaluation of Bromadiolone Against House Mouse (Mus Domesticus) Populations in Irrigated Soybean Crops. I. Efficacy of Control.

Abstract

The effectiveness of bromadiolone for controlling breeding house mouse [M. musculus] populations in irrigated soyabean crops was tested when mouse densities were around 200-300/ha. A single application of wheat with 0.005% bromadiolone, placed in bait stations (200 g/station) 20 m apart throughout the crop, effectively reduced mouse numbers at 1 of 2 sites. Where few other irrigated summer crops were close by, bromadiolone reduced mouse numbers relative to the unbaited control by 43-62% within 22 d, depending upon the index of mouse abundance used. Because of a general decline in mouse abundance after this time, the effect of baiting lasted through days 22 to 42. The overall benefit from baiting was marginal, because mouse numbers just before harvest (42 d after baiting) were still around 43% of pre-baiting levels. Where other irrigated summer crops were in close proximity, the single application of bromadiolone did not reduce mouse numbers, and there were no effects which could be attributed to baiting, either at day 22 or 42. Although few marked individuals survived baiting, mice from neighbouring crops apparently replaced those killed. When the baiting trials commenced, growers had just become aware that mice were causing noticeable damage to soyabean crops. By this time, mice were evenly distributed from 0.5 to 90 m into the crop and, as the mean movement of resident mice was 10.9 m, perimeter baiting only would have been ineffective. It was concluded that the distance between bait stations in irrigated soyabean crops should not exceed 20 m.