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Each January, right after the New Year, we turn our attention back to the orchard. It’s bare root fruit tree planting season!

Last summer we noted that two fruit trees in our orchard had sustained significant damage as a result of Meadow Voles.  Last spring, for the first time, we had an explosion of Meadow Voles in the orchard and gardens, that caused significant damage to a number of plants.

Voles stripped the base of this tree of bark, and also damaged roots

As we don’t use poison baits on the farm, we elected to trap the voles, which is a lot of work, but with perseverance we were modestly successful at decreasing their populations.

We find conventional snap traps to be the most effective at catching voles

However, voles are active night and day, 365 days a year, and their populations can quickly rise again.  As an acre of land can support up to 500 voles, vigilance year around is critical to sustained control.

To prevent their populations from rising again this spring, addressing the voles now, in winter, is important to minimize our potential for damage later in the year.

Meadow Voles can become plentiful where there is ample feed, and ground cover to protect them from predators

As we don’t use baits, we’re left with with habitat management, and trapping, as our best options for controlling our vole populations.  Voles live in burrows underground, and use vast networks of surface runways to travel from burrow-to-burrow.

Voles prefer to travel under cover, so we cover our snap traps with metal covers

In the winter months, which is when most of the damage to plants occurs, voles can move around relatively undetected.  They can construct their surface runways through snow, or protective vegetative cover.  This enables them to avoid predation.

The most important thing we can do for vole control this time of year, is remove as much protective ground cover as possible near the fruit trees to force the voles out into the open where they’re exposed to predators, like owls, and hawks.

Predators, like this Red-Shouldered Hawk in our orchard, will catch voles, if they can see them

Removing the ground cover also removes the primary food source of the meadow voles, forcing them to go elsewhere to feed. [1,2]

Vole holes are small and round. They don't make mounds of soil like gophers, nor do they push up surface soils like moles.

We’ve already noticed a few new tunnel entrances appearing on the orchard slope, so the past few days we’ve been removing all of the vegetation on the slope, except for the fruit trees.  Sadly, this will mean few to no wildflowers in the orchard this spring.  We’ll miss the flowers, as will our bees, but it’s a small price to pay compared to the extensive damage these tiny furry rodents did on the farm last year.

No Goldfields in the orchard this spring, they provide too much shelter for meadow voles

There is a suggestion that voles dislike crown vetch (Securigera varia)[1], which should thrive on our sunny orchard slope, and could be planted as a ground-cover to curb erosion, and to discourage the voles.  However, this species is toxic to livestock, so for now at least, we’re opting to simply keep the ground clear.

With the vegetation cleared, for the remainder of the season we will need to be vigilant, keeping the grasses and weeds down as low as practically possible.  Last year, with unrelenting rains, this was somewhat challenging, but so far this season the weather appears to be working in our favor.

With the slope all but scalped over the last few days, we then inspected the base of every single fruit tree in the orchard, as now is the perfect time for us to acquire replacements for any damaged trees.  Vole damage, unlike deer, or rabbit damage, can frequently go undetected, so cursory visual inspections aren’t enough.[4]

All of our trees were fitted with both gopher wire around the roots, and with vole guards protecting the trunks at time they were originally planted.  However, it was clear last year that the voles managed to defeat the trunk guards.  Yesterday, we raised up each vole guard so we could inspect the trunk of every tree, and then the surface soil was pulled back all the way down into the root zone.  This is because vole damage often lies below the soil line.

This is our Frost Peach. The damage caused by voles was entirely below the soil line, where the bark and cambium were stripped.

We knew the damage to our Frost Peach and our Bosc Pear trees last season was significant, so in November we had pre-ordered replacement trees.  Our trees arrived just in time for the New Year, so yesterday we set out to remove the damaged trees.

It was so difficult to bring ourselves to dig out the peach tree.  To our surprise there was already noticable bud swell on this tree, and the upper branches seemed remarkably healthy.   The canopy did not even hint at the severity of damage below the soil line though.

From above, the Frost Peach tree looked remarkably healthy, forming plenty of buds for spring.

Removing the soil around Frost, the magnitude of damage was readily apparent.  At least 50-60% of the bark and cambium below the soil was gone.  Not only that, but all of the major roots on the down-slope side of this tree were also severed.

I could push my hand completely under the base of this tree, as so many roots were missing

Although this peach tree may survive this damage, and not die, the size of this defect around the trunk, and the missing roots, will significantly impede the flow of nutrients to the canopy.  Last summer, the first clue something was wrong with this tree was that the leaves were continually wilting during warmer weather, when all of the other trees, including a neighboring Indian Free Peach, were just fine.  This tree will always be set back, vigor will be always be reduced [3], and fruit set will never be optimal, so yesterday, reluctantly, we removed this Frost Peach from the orchard.

With the tree removed, and the damaged area rinsed, you can clearly see where bark is missing (yellow arrow)

We replanted with a new, healthy Frost Peach tree, on the same rootstock.  Although the replacement tree was healthy, with a good trunk caliper, the graft union itself left a lot to be desired.

This is not an ideal graft union, as too much rootstock extends above the graft

Too much root stock base protruded above the union, and left in place this could potentially trap soil or plant debris, and hold water against the trunk.  Before this bare root peach was planted, we carefully removed the excess root stock, cutting at an angle to ensure it sheds water.

By trimming the excess rootstock, we'll prevent soil and debris from trapping moisture against the trunk

The cut was then wrapped in Parafilm to prevent the cut from desiccating while it heals.

In an attempt to prevent the voles from defeating the vole guards again, we modified the base of all of the guards on all the trees in the orchard, by flaring out the base slightly to ensure the bottom of the guards follows the angle of slope on the hill.  We’re hoping this will make it somewhat more difficult for the voles to cheat underneath the guards.

We've now toed out the base of each vole guard, and molded them to follow the angle of the slope on the hill in the hopes of preventing the voles from easily digging under

We’ll keep the vegetation cleared in the orchard, and cross our fingers that the owl box we built and installed over summer will find itself with a new vole-hungry resident moving in this spring.

We're hoping some hungry owls move into this box above the orchard this spring

As for the Bosc Pear, we’ve chosen to leave this tree in place for another season.  Although approximately 25% of the tree was girdled at the base, the damage has healed somewhat, but to hedge our bets we’ve planted the replacement tree nearby.

On closer inspection, the damage to Bosc was relatively less severe, so for now we've chosen to leave it in place

Best case scenario we’ll have two trees of the same variety in the orchard, but if the damaged Bosc fails to thrive and needs to be removed, its replacement is already in place.

In the meantime it will be up to us to keep a very watchful eye on the rate of vegetation growth in the orchard over winter and spring, especially once our rains return…at least we hope our rains return as right now we’re only just over 30% of our normal winter rainfall for this time of year.

We may never get rid of voles completely, but hopefully with good management we can keep their numbers within tolerable limits, and minimize potential for damage.

We're looking forward to our replacement Frost Peach producing these beautiful pink blooms in spring

It will take a couple of years for the new Frost Peach tree to set fruit, but we’re looking forward to making peach jam again in the very near future.

In the meantime, we’re excited that fruit tree grafting season is also upon us.  The San Francisco and Monterey Bay Area Scion Exchanges, hosted by the California Rare Fruit Growers, are coming up in January:

January 15, 2012: Monterey Chapter Exchange, Cabrillo College, Aptos, Santa Cruz
January 21, 2012:  Golden Gate Chapter Exchange, Laney College, Oakland
January 22, 2012:  Sacramento Exchange, Cooperative Extension Offices, Sacramento
January 28, 2012:  Redwood Empire Chapter Exchange, Veterans Hall, Sebastopol

For more information regarding these events, see here.

Scion exchanges are an excellent place to acquire material for grafting rare, unique heirloom fruit varieties, that aren’t readily availabe in area nurseries.  Last season we grafted a number of apple and crab apple varieties.  Who knows what we might find this year!?

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[1] Identifying and Preventing Vole Damage. Colorado State University Extension.

[2] Protecting Trees from Vole Damage.  Extension Notes.  Ontario.

[3] Pearson, Karen.  1977.  The Influence of Pine Vole Damage on Apple Tree
Vigor and Fruit Yield
.  Eastern Pine and Meadow Vole Symposia.  University of Nebraska.

[4] UC IPM Online.  How to Manage PestsPests in Gardens and Landscapes.  Voles (Meadow Mice)