Integrated Pest Management Guide

TOWNSEND'S VOLE, Microtus townsendii (Bachman)

Pest Status: These vertebrate mammalian pests are often found in cranberry beds. Since Townsend's vole is common in agricultural lands in the Lower Mainland, this species is most likely to be the one found in cranberry fields.

Life cycle and feeding habits: Voles, also called meadow mice, field mice, short-tailed mice, or orchard mice, are small short-eared, short-tailed rodents. Townsend's voles produce their litters continuously every few weeks from April through October, or later. They may have up to nine young per litter per female. All voles are plant feeders. Townsend's voles eat crowns and roots of grasses, sedges and other succulent herbaceous plants. They also feed above ground on seeds, bark and leaves. These small rodents tunnel through cranberry beds. They cause damage by feeding on the roots and by cutting the vines. Voles are active day and night in all seasons. They spend most of their time underground or in dense grass. They are the main food source for many birds of prey. Crows also feed on them. Townsend's voles are considered good swimmers and dive readily.

Observation of damage and detection: The first signs of vole activity are 2.5 - 3.7 cm (1 - 1.5 inch) open holes in the ground with connecting compacted paths. Voles cut vines along the corridor of the main run. Because voles confine most of their above-ground feeding to these paths, clipped vegetation can generally be found around the open holes and along runways. If you were to begin digging at one of the holes you would find a second runway, just below the soil surface, where these animals spend the rest of their time feeding on plant roots. Digging a little deeper, you would find another set of burrows 15 - 25 cm (6 - 8 inches) below the soil surface where they store food, build nests, and rear their young.

Control: Non-chemical approaches:

• frequently mow ditch banks to reduce food and protective habitat for the voles;
• encourage raptors such as owls, hawks, and kestrels by mowing ditch banks to allow easier visual contact with their prey; and
• flood if possible.

No rodenticide baits are registered for vole control within the beds. Therefore, only bait stations placed off the beds can be considered. Several bait stations should be used around a bed. It is not necessary to treat the entire area, but only those edges adjacent to vole habitat. Best control with all baits will occur with applications in fall or winter when food is scarce. There are several types of bait stations. PVC pipe 2.5 - 4.4 cm (1 to 1.75 inches) in diameter, constructed in an L-shape or upside-down T-shape, makes an excellent bait station. The horizontal pipe should be at least 30 cm (12 inches) long so that bait does not spill out the end and so that it will stay dry. Zinc-phosphide baits should not be reapplied within 90 days of a previous application because voles become bait-shy due to the fast action of these baits. The anticoagulant baits kill after 3 - 5 days of continuous feeding. More than a single feeding is usually necessary with anticoagulants.

Fill the tube no more than one-quarter full with bait if the tube is closed at one end. If the tube is open at both ends, coat the bait with syrup to stick it to the inside of the tube. Remove uneaten bait from stations. All baits are attractive to domestic pets and also kill non-target birds and other wildlife. It is very important to avoid injury to non-target animals. Do not pile the bait. Pick up all spills. Dispose of bait properly.

To estimate the degree of control obtained by using baits, put apple pieces in vole runs before you put out bait and monitor the number of munches after 12 hours. Then follow up with more apple sections a week or two after you put out the bait.
 

Townsend's vole

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