Wednesday, November 30, 2016

Strategies for Vole Management

The following article By Indiana Joe appeared in the Summer Issue of WCT Magazine. Voles are a common pest in North America, and present multiple challenges in effectively mitigating the damages caused by this rodents behavior. In this article we outline an effective IPM strategy for the control of Voles, and discuss why the classical reliance on rodenticide baiting is proving to be less than optimal. Introduction The name "Vole" refers to any species in the genus Microtus, also known as the meadow mouse. They have small eyes and ears,short tails, and dark fur. Around 23 species occur in North America, but 3 species are of most concern to PMPs; the meadow vole, the prairie vole, and the pine vole. Although there is overlap in the preferred habitat of each species, usually only one type is found in a given area because of species competition and separation from the others by either an ecological or a geographical barrier. PMPs must consider the location, species, and type of damage before planning an effective IPM strategy. The prairie vole (Microtus ochrogaster) has a medium length tail and inhabits grassy fields, mixed deciduous woods and tall grass adjacent to wetlands or seasonal ponds. The meadow vole (M. pennsylvanicus) has a long tail and inhabits wet marshy areas, grassy stream sides and drier, grassy fields. Meadow voles are more of a surface dwelling species and rely on trails or runways as opposed to other species which are more subterranean in habit. The pine vole (M. pinetorum) has a short tail and is found in woods along wetlands, meadows near trees and shrubs , and where-ever mixed grasses and various forbs (broadleaf plants) are in the undergrowth. The pine vole has a more underground lifestyle than the other two, making tree wraps and baits less effective. It is interesting that the vole that has the shortest tail also spends the most time underground, where a long tail might get in the way. In general, all voles are semi-subterranean, and prefer areas with heavy ground cover. Most species of voles live in colonies. They occupy a variety of habitats, but are mostly associated with grasslands. They are active all year, both day and night. They feed on a variety of plant materials (and the occasional insect or snail) and their feeding preferences shift through the seasons. They reach sexual maturity in a few months and females can have 5 or more litters per year with 3–6 young per litter. Voles breed throughout the year, with peaks occurring during spring and summer. Voles damage lawns, golf courses and gardens with their above-ground runways and underground tunnels. Girdling of woody plants by voles can reduce the yield of fruit and even kill trees. Tree damage is most common during the fall and winter when other foods are limited. Damage to trees may not be readily noticed because the root gnawing and stem girdling often occurs under the cover of snow. Once signs of damage are noticed the trees have already received substantial damage. Management Although rodenticides offer an easy solution, they are both expensive and potentially hazardous to non-target species. There is also the potential of the target animals developing resistance and/or “bait-shyness”. Rodenticide use should be in combination with other control measures such as trapping and exclusion. Monitoring Vole population can fluctuate throughout the year, so monitoring is essential. The most useful method of monitoring voles is called apple-indexing. Apple slices are weighed and strategically-placed in the animals runway system or burrow for 24 hours. Then weigh the apple slice again and figure about one vole for every half ounce of apple eaten. This will give you a ballpark figure for the number of voles you are dealing with. The slices with the most damage are the areas most at risk. Habitat management This includes elimination of weeds, ground cover, and litter around lawns and ornamental plantings. Lawns should be mowed regularly. Vole pathways are chosen in proportion to risk associated with travel. In other words, they are more likely to take a long trip to get food if it has cover from predators than a short trip that would expose them to danger. Survival rates are lowest where dense cover is not available Exclusion If the voles are damaging trees, you can create a buffer zone around them by clearing mulch 3 feet or more from the base of trees, and placing hardware cloth tree wraps on the trunks. The mesh size of the hardware cloth used to construct tree wraps should be no larger than 1/4 inch in size. The tree wrap should be buried at least 6 inches below the ground surface to ensure that voles will not burrow under the hardware cloth. Biological Control A large variety of predators prey upon voles, in fact the short-tailed weasels specialize in hunting voles. Their diet can be up to 98% percent voles. Perches and nest boxes for avian predators such as kestrels and red-tailed hawks can be found or constructed. Hiding places for predators such as foxes, snakes, and feral cats can be incorporated into the landscaping. Repellents Repellents may provide a little protection for plants, but their effectiveness usually is temporary. If you've ever been to the city dump, you know that the smell is terrible at first, but pretty soon you get accustomed to it. It's the same with repellents. Undesirable groundcovers may be used around the perimeter as a deterrent by including unacceptable food items, such as crownvetch, myrtle and endophytic grasses such as fescue and perennial rye. Electronic devices have very little effect. Trapping The good old snap trap is very effective in reducing numbers on small to medium sized jobs, but it is labor intensive and may only be useful as a monitor on bigger jobs. Snap-traps should be placed at right angles to the runways and flush with the ground. Do not prebait in an attempt to increase trapping success, as there is no difference in trapping success in prebaited traps compared to non-prebaited traps, but non-target species are more likely to be caught. In fact many times bait isn't necessary at all; the voles will set off the traps as they run through their pathways. Live-trapping and pitfall-trapping can also be used. Rodenticide baits Baiting is most effective in winter, when populations are low, and food is scarce. Bait acceptance will be higher and secondary poisoning of non-target species will be less likely. Baits should be hand placed at burrows or placed in runways. Bait must be dry and fresh or it will be rejected by the animals, so a shingle or small board can be used to protect it from the snow. Fumigants are of limited utility due to the complexity of the network of tunnels. Voles are an integral part of their ecosystem. They reduce sagebrush in rangelands thereby increasing grazing productivity, they aerate the soil, and they offer food to numerous types of predators. As such they should only be controlled when they come in conflict with human needs.

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