Eenie, Meenie, Miney, Vole

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Blueberry growers are learning more about controlling voles in their fields thanks to the work of Sofi Hindmarch, who wants to educate and help reduce the volume of rodenticides used in local fields. She also wants to see vineyard managers take more of an integrated pest management approach (IPM) when it comes to voles, like the vineyards in California do with pocket gophers.

Hindmarch’s work with barn owls and other raptors around the Lower Mainland is known by many in the agriculture and conservation industries. She is part of a team working on sharing vole research and information with growers, which has been partly funded through grants from the Investment Agriculture Foundation, Fraser Basin Council, Abbotsford Community Foundation and the BC Blueberry council.

“Voles are the only small mammal that causes damage to the blueberry bushes,” Hindmarch says.

She adds that they will also harm grape vines in a similar fashion. Voles will eat the roots of the plants plus they will also munch on the bark of mature plants, girdling them.

“We just want to make sure that when a farmer sees a mammal that he knows what type it is,” she notes. “So that he doesn’t start putting out poison when he sees a deer mouse for example, because deer mice don’t do any damage to blueberry fields.”

The overall objective for the project - which includes fact sheets and video on the BC Blueberry Council website - is to get growers to think differently about rodenticides.

“The goal is to ensure that rodenticides are only used as a last resort in an effective manner in a farm, agricultural setting,” Hindmarch says. “We’re basically ensuring that farmers have a knowledge level of which type of mammals make the damage in the blueberry fields.”

The project has several levels that apply to both blueberry fields and vineyards. The first is landscape management to make the field unappealing if voles aren’t yet present. The second is to ensure growers can identify what mammal they have in their field, so that rodenticide isn’t used on just any small mammal seen in the field. The third is to know which rodenticides are allowed for use in a field and that they are used in the most effective manner. Finally, owl box installations are being offered as part of a larger IPM strategy.

Identification 101

The Townsend’s vole is the trouble-maker growers need to keep an eye out for. It is a larger rodent of typically 45 to 90g and 11 to 14 cm in body length, with chocolate brown fur that hides the ears. It also has a relatively short tail of less than half the body length.

Deer mice are very common and are much smaller (15 to 25 g) with light brown to grey fur, visible rounded ears, long tails and they tend to hop along the ground rather than run like a vole. Shrews and moles are often in blueberry fields but are seldom seen.

The primary way to determine if a rodent is a vole, mole or mouse isn’t just through appearance, but from their tunneling. Voles leave holes in the ground of about five centimeters in diameter, whereas the mouse holes are much smaller at about two-and-a-half cm. There are no dirt piles over vole holes – that is a telltale sign of a mole (which eats worms). The tunnels of voles are also often visible on the surface of the ground as runway depressions that lead to holes and deeper tunnels. The highest vole densities often occur in fall and winter and their tunnels are commonly seen after a snow melt.

Voles like to burrow along the rows of blueberry bushes and grape vines, giving them easy access to roots and stems for food. Some of the signs of feeding on blueberry bushes include parallel grooves from front teeth, scratch patterns in various directions, damage is above or below ground and any damage will also have tunnels and runways nearby.

While weevil damage may mimic vole damage, the differences are the lack of parallel teeth grooves (as opposed to random scratches weevils cause), a presence of weevil larvae, leaf notching from adult weevils and a lack of vole tunnels and runways.

According to Hindmarch, monitoring shows that fields with less vegetation (or shortly mowed grass), that flood and aren’t next to grassy fields will experience a lower number of voles.

“We want to reduce the amount of rodenticide in the agricultural landscape,” she says. “The best way is to be targeted and efficient in manner. [Farmers have] been defaulting a lot to just putting out rodenticides all the time. We want them to use it over a short period of time, assess whether it’s working or not and then they remove it from the field when it’s reduced the damage.”

Both the fact sheets and the video (which is in the works) will be available on the BC Blueberry Council website.

“It’s trying to reach people in an easier media,” Hindmarch says. “Everyone’s got a phone and if they can look at those videos on the phone or a short visual, instead of a loose fact sheet that’s going to end up in your catch-all drawer and then in the recycling bin, that means they can just download it right there in the field.”

While blueberry fields are a main issue Hindmarch notes that the pocket gopher, which causes trouble in California vineyards, is often controlled with barn owls.

“Barn owls are used quite extensively in grape fields in California as part of IPM. They try to encourage barn owls there,” she says. “There it’s pocket gopher that’s kind of the equivalent of our vole.”

The project is intended to be a new way for growers to monitor rodent issues, identify them and take the appropriate action.

“Not only are we making those videos, we’re hoping to create a potential monitoring program for farmers so they can assess the presence of voles,” she says. “Fresh droppings, fresh vole runs, an idea of their abundance and how current it is so they’re not just putting out rodenticide in the fall without even knowing if there are voles in the field.”

Hindmarch says that growers are quite receptive to the approach and that misuse of rodenticide is accidental in her opinion.

Rodenticides approved for use in fields include brands like Ground Force, Ramik Green and Ramik Brown with have the approved active ingredients of chlorophacinone, diphacinone or zinc phosphide. But, Hindmarch would rather see raptors like barn owls or hawks used to control vole populations and continues to set up nest boxes for farmers and advise on where to place perching poles for other raptors.