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Doug Ransome
Vole
The Townsend vole is less common than the meadow vole, but tends to be more destructive to farmer’s fields.
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© Brian Kushner | Dreamstime.com
Deer
Deer can be repelled by human hair, soap and lion dung.
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Doug Ransome
Meadow Vole
The Meadow vole is often called a field mouse in Canada, but is a different species.
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© Jiri Castka | Dreamstime.com
Rabbits
One of the most effective methods to deter rabbits is fencing about three feet high, with the bottom six inches buried to prevent digging.
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Doug Ransome
Vole
The Townsend vole is less common than the meadow vole, but tends to be more destructive to farmer’s fields.
Time to put a ‘Stop to the Pests with Backbone’
Part of the appeal of being a fruit grower is spending time outdoors communing with nature. The birds, the bees, the wildlife – it’s all part of Mother Nature’s big happy family unless some of Mother’s children begin to exhibit too much backbone in your field or orchard.
You take action or face serious losses. Whether large mammals, rodents or birds, the creatures snacking on your property are known as vertebrate pests.
The starling is the most obvious, but this article will focus on ground-based pests, the small, furry mammals that farmers find neither cute nor cuddly.
Small vertebrate pests include voles, mice and gophers – of those, the vole is generally the most destructive. These hungry rodents eat roots and can destroy an entire operation.
In his talk at the January Pacific Agriculture Show, Mark Sweeney, BC Agriculture’s berry industry specialist, said, “Voles are a growing problem.”
Voles and mice are different species, yet look and behave similarly. They hide under weeds, leaves and other ground cover prompting many orchardists to create weed-free strips between trees. Removing debris and material piles will aid in denying rodent-friendly refuge. Wood mulch has been used effectively in some regions, but damp climates break down the chips to a soil-like material, allowing for tunneling.
“What works in one region may not work in another,” Mullinix says.
Douglas Ransome, a fish, wildlife and recreation program instructor with BCIT, notes voles seem to prefer high vegetation sites, but studies are still underway to determine the relationship between vegetation and voles.
“We’re not sure yet,” he says. “Many of the sites [studied] with grass have encountered voles. It looks like grass has a role in population, but we’re uncertain what that means for [crop] damage.”
Thus, having voles doesn’t always equate to crop damage.
“We don’t know when [a trigger to damage] happens,” Ransome notes.
Voles can reproduce every 21 days sometimes causing “eruptive population cycles.” Studies about the tipping point that causes a population explosion are underway. It is during this growth from one or two voles per hectare to 600 to 800 that crop damage occurs.
Coastal based growers on Vancouver Island and the Lower Mainland are faced with the tunneling Townsend vole’s tricky behavior.
Ransome notes, coastal growers are “really kind of stuck. I still tell farmers to definitely put up perch poles [for raptors], but when you start getting hundreds per hectare, the predators can’t control them.”
Ransome says it is assumed that these, high volume years force voles to turn to crops as a food source.
Trapping is difficult with mice and voles, but is more effective with gophers according to Mullinix. Other possible solutions for small rodents are propane torching of runs and poisoning.
Poison may seem like the easy answer, but organic farmers can’t use rodenticides and poison frequently harms helpful raptors and snakes.
In her study of raptors for Delta Farm & Wildlife Trust, Sofi Hindmarch explains that modern anti-coagulants have the most toxic effects. These poisons have been found in many of the raptors studied. It is unknown what levels of secondary poisoning will kill or disable a raptor.
“The doses are very small, but it is very toxic,” Hindmarch says. “Definitely think twice before putting rat poison out.”
In a study of dead owls, 70% had traces of poison in their liver. Generally, this comes from secondary toxicity (from eating prey that has consumed the poison), but in some cases birds access the poison directly.
Ransome says in his studies of voles in fields he has found the majority of farmers have used poison, at least sometimes.
Mullinix confirms this and further comments, “I do not have any statistics, but in my experience most conventional perennial fruit crop farmers would feel it appropriate to poison small rodents…because they can do extensive damage quickly.”
With little alternative control available, poison has become an acceptable solution, though not necessarily a comfortable one.
“I think we need to do more work to develop biologically based integrated vertebrate pest management methods and strategies,” Mullinix says. “[Poison] disrupts or preclude biologically-based systems, disturbs and diminishes the ecological complexity and hence the integrity/resilience of our agro-ecosystems. [It can also] directly harm pets and other off target species [like] people.”
Mid-sized pests with attitude include beaver and rabbits. Everyone knows how difficult beavers can be; they won’t give up a good home, so trapping and relocation is essential. Because the over-sized rodent doesn’t climb or jump, flaw-free low fences can be effective. Fortunately beavers only damage trees. They are seldom interested in cane or bush crops.
Rabbits take delight in the bark and vascular system of trees just above snow level, thereby girdling it. They will also dine on new shoots, leaving many plants at risk.
One of the most effective methods to deter rabbits is fencing of about three feet high with the bottom six inches buried to prevent digging. Rabbits are not long distance travelers – they stay within a radius of about 20 acres – so deterrents need to encourage the rabbits to stay out of the production area. Search the internet and you’ll find a number of repellent ideas from human hair to lion dung. If you can control rabbits this way, the key to continued success is regular replacement.
Like mice and voles, desirable rabbit habitat needs to be removed – debris piles, dense vegetation and rock piles. Rabbits are also controlled by raptors; and a dog or two running the field will further deter them. Ultimately, because of their high reproductive ability, it takes a combination of methods.
Some vertebrate pests are a problem simply because of their size. Deer, elk and bear can trample, crush and swat plants and trees.
Combined with this unintentional damage is regular feeding. Deer and elk eat both fruit and new plant buds.
“Deer and elk [graze] on shoot tips during the winter dormant season and can remove all terminal buds as high as they can reach,” says Mullinix.
Control methods are similar to that of other pests. Repellents like human hair, soap and lion dung may be effective, but deer and elk are quick to habituate. Flawless fencing is an effective option, but the expense can make it prohibitive, especially given the height necessary.
Mullinix states one of the best deterrents he witnessed was a Great Pyrenees dog. The nocturnal and protective behaviour of the dogs make them excellent herd guardians as well as family pets.
Eliminating high vegetation and other nearby cover will help control bears along with picking ripe fruit quickly and keeping the ground clear. Motion sensors can be a deterrent, but bears too are easily habituated. Electric fencing is perhaps the best bet, but it must be operational before the growing season begins as bears will proceed through the fence if they are already food conditioned.
It’s time for you to gently push back some of Mother Nature’s creatures. If the pests in your orchard or field are exhibiting a little too much backbone, identify the pests and take responsible action to ensure your crop has the best chance possible. ν
