Vole control made simple
It could be as easy as bettermanagement of vegetation around crops.
By Judie Steeves T
he problem with voles in berry fields might be resolved by simply reducing the vegetation between rows, and keeping plantings away from fields where grass dominates, since grasslands are their favoured habitat.
Small mammal biologist Doug Ransome, who heads up the ecosystem restoration program at the B.C. Institute of Technology, has been studying the Townsend’s Vole (Microtus townsendii) in Lower Mainland berry fields since 2013. He produced a progress report this spring detailing what he’s found so far.
He reports that “seldom were voles captured in blueberry fields that had very low levels of vegetation, with minor captures in fields with medium levels of vegetation.” Only one vole was captured in blueberry fields with low and medium vegetation cover in three years of the study.
for habitat.
At this point, he says he hasn’t actually found significant damage to berry fields, except one, located adjacent to a grassy field.
He did note that in the 2014-2015 year, half the voles were captured in one blueberry field which had high levels of grass. It was also adjacent to a
DOUG RANSOME Vole caught white-handed in blueberry field. Ransome
If fields remain dry during winter, or are adjacent to fields dominated by grass, that could tend to artificially concentrate voles into blueberry fields during winter, resulting in chronic damage, he reported.
However, since vole populations tend to be cyclical, Ransome says he would be more comfortable with the accuracy of his initial findings when voles are in high abundance, when he can determine whether the same pattern continues.
He says vole numbers appear to have been at the low end of their cycle during all years of the study so far.
It may be that when vole numbers are at the high end of their cycle, they will move from their favoured grassy fields, into blueberry fields, due to competition
8 British Columbia Berry Grower • Summer 2016
forage field that appeared wet, with periodic flooding. He feels the voles may have fled to the nearby blueberry field whenever the forage field flooded. Ransome’s research included live-trapping the voles in blueberry fields with low, medium and heavy levels of vegetation as well as in grass fields, as a control plot. He found that the most voles were captured in fields with the heaviest levels of vegetation—whether they were the control fields or
blueberry fields.
By contrast, the majority of captures in the first year were deer mice rather than voles and most of those mice were
caught in fields with low levels of vegetation, he reports.
A clear indicator of the amount of vole activity is after snowmelt, when the runways are visible on top of the ground.
In fact, he suggested monitoring the relative abundance of runways may provide a reliable indicator for growers to assess the level of vole activity in their blueberry fields, which can then be used to evaluate the need for using rodenticides.
He noted that Townsend’s voles tend not to move very far from their primary activity area, so in fields with a high abundance of voles, the density of bait stations for rodenticides should be increased or they should be moved around on a regular basis.
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