Hi Karl: Here is an article that I have written for our growers on vole
control. It is more organized than the way it looks in this cut and paste.
I will be happy to send it to you as an attached file.. Mosbah Kushad,
University of Illinois
VOLE (MICE) CONTROL IN COMMERCIAL APPLE ORCHARDS
by:
Mosbah M. Kushad
University of Illinois
Vole damage to apple trees in Illinois and many mid-western states
can be devastating unless preventative measures are taken to reduce their
population. In Illinois, vole population is very high, especially from
Spring to early Fall when there is plenty of grain and vegetation for these
animals to feed on. Tree damage from vole occurs during late Fall to early
Spring, particularly if the ground if covered with snow. During this
period, there is very little vegetation for these animals to feed on,
because corn and beans have been harvested and the ground cover is frozen or
dormant. As a result, the animals will likely feed on less desirable woody
plants such as apple and occasionally peach trees.
Vole Species
There are three species of vole in Illinois and most of the mid
western states. These species are:
a. Pine vole (Pitymys pinetorum). This species has a relatively small
body, short tail (about the length of the hind-leg), a pointy nose, sunken
eyes, and a brownish fur. Pine voles are usually very shy of venturing into
the open, so they tend to feed mostly underground on young root and root
bark. Pine voles are very damaging to apple trees, because it is very hard
to detect injury to the root system until it is too late to save the tree.
It is also difficult to correct the problem by bride grafting.
b. Meadow vole (Microtus pennsylvanicus). This species has a larger
body than pine vole, it had a longer tail (about two times the length of the
hind-leg), prominent eyes, and dark grayish fur. Meadow voles are less shy
than pine voles and so they tend to feed in the open, especially if there is
enough groundcover to hide under. They will also feed immediately under the
soil surface. Most of the injury to apple trees from this species occurs at
the soil surface. They use their sharp teeth to peel off the bark,
especially of young trees. However, the damage is not restricted to young
trees, I have seen twenty year old trees girdled by meadow voles.
c. Prairie vole (Microutus ochrogaster). This species is very similar
to meadow vole in appearance and eating habits.
Identification of Vole Species and Population Monitoring
Growers need to determine the potential for tree damage before they apply
any treatment. Vole species and population size are two very important
factors for predicting the extent of the damage and for deciding on what
control measure are needed to reduce the population.
To identify vole species in an orchard, place approximately 20 traps
per orchard close to active runs and in heavy cover areas. Measure the
length of the tail relative to the hind leg. If the tail is very short
relative to the hind leg and the fur is brownish, then it is likely that it
is a pine vole. However, if the tail is about the length of the hind leg
and the fur is grayish, then chances are it is a meadow vole. Estimate
percentage of the population is pine versus meadow vole. As I will discuss
in the chemical control section, it is important to know what percent of the
population is pine versus meadow vole.
The most effective way of determining vole population is to place a
half apple close to tree trunk or at the site of an active run. Depending
on the size of the orchard, place an apple slice every 4 to 5 trees in an
orchard of 2 to 3 acres. In larger orchards, place an apple slice every 20
to 30 trees in each block. Distribute the apple so they are not close to
one another. If there are shrubs adjacent to the orchard, place an apple
slice every 10 to 20 feet in that area as well. Approximately, twenty-four
hours after placing the apple slices in the orchard, check them for gnaws
(teeth marks). Percent of apples with teeth marks will give an approximate
percent of trees that will be damaged if the vole population is not
controlled.
Orchard Vole Control Program
a. Non-chemical. Mowing on a regular basis, especially during early
fall, is the most effective treatment for vole control. When mowing an
orchard, it is as important to mow between the trees as it is to mow within
the row. Any tall grass between the trees will likely be a haven for pine
and meadow vole. I have seen an apple orchard in Illinois in 1994 where
every tree within a row was damaged by voles because the grower failed to
mow between the trees. It is also important to keep a clean area of about
150-200 feet around the orchard to prevent any meadow voles from moving into
the orchard. Such practices can cut vole population by more than 50% in any
given year. A herbicide strip or a circle around the tree can also be
effective in reducing pine and meadow vole populations. Herbicide strip
alone, however, will not eliminate the problem of vole damage, especially of
meadow voles. When combined with chemical treatment, herbicide strips will
reduce vole populations. Another important non chemical practice is to
encourage vole predators to move into your orchard. A good example is to
encourage cats to live in and around the orchard. Also build an observation
tower for owls, hawks, and other predatory birds. This observation tower
can be as simple as a 10 to 15 foot pole with a "T" top.
b. Chemical baits. At the present, there are two types of chemical
baits available for vole control in apple and peach orchards. These baits
are: Acute baits (Zinc phosphide) and anticoagulants (Chlorophacinone and
Diphacinone). Deciding which of these chemical baits to use depends
entirely on the vole species. Although these chemicals will provide some
control of both vole species, zinc phosphide has been shown to be more
effective against meadow vole, while Chlorophacinone and Diphacinone have
been shown to be more effective against pine vole. Zinc phosphide baits are
marketed either as weather resistant pellets or combined with several types
of grains, such as cracked corn and oats. When vole population is very high
an additional application of zinc phosphide may be made within 1 to 2
months. Zinc phosphide grain baits applied by hand were found not to be
very effective against pine vole, however, better control was achieved when
apple slices were coated with zinc phosphide liquid at the rate of one
teaspoon per quart of water. Phacinone baits are marketed in a weather
resistant pellet form. Several days of continuous feeding on these
formulations are needed for an effective control. A second application may
be added within 3 to 4 weeks after the first one, but not within 2 weeks,
because the first application will not take its effect until about 18 to 20
days.
Methods and Timing of Bait Application
Baits can be applied in several different ways, however, not all of these
methods are effective.
a. Hand baiting in the active run. This method involves placing baits
in the active runs at each hole. This method is very effective, however it
is not practical in large planting with sever vole population. An
alternative method is to place the bait under a bait station, as will be
described in the next section. This method is more practical and effective
for vole control. It is also less hazardous to other animals and birds in
the orchard.
b. Broadcast baiting. This method is effective for control of meadow
vole, but not for pine vole. Other animals and birds may be harmed by
broadcast bait and, therefore, it is not recommended.
c. Trail baiting. A trail building machine may be used to apply the
bait in furrows. This method is not very effective for control of meadow
vole and only slightly effective for pine vole.
d. Spray. Zinc phosphide spray in late fall was found to be somewhat
effective against meadow vole population. However, this practice is harmful
to the environment and to other animals and, therefore, we do not recommend
it.
Placing bait by hand under bait stations is a better way of controlling
voles in apple orchards. The best time to apply these chemicals is late
summer through early spring when there is little vegetation for these
animals to feed on.
Bait Stations. The most effective bait station is the one that will provide
dark shelter with some ventilation to prevent the bait from molding.
Shingles, PVC pipes, metal sheets, split tires, and many other types of
stations have been used to cover chemical baits. Metal stations may damage
the blades of mowers. If you do use metal stations make sure to remove them
in early spring. Ross Beyers from Virginia found that split tires were
more effective than other stations that he tested. The tires are split in
half along the thread.
It is very important to place bait stations in the field by mid
summer so the animals will get accustomed to their presence. However, there
is still time to place the stations before any snow buildup.
General Recommendations.
1. Mowing is critical especially during late summer and early fall to
prevent any over growth. Mow between rows and between trees in each row.
2. Remove any shrubs and tall grass at least 200 feet around the
orchard.
3. Never place straw or any type of mulch around the tree that will
attract vole.
4. Place bait stations 2 to 3 months before baiting.
5. Check bait periodically for mold.
6. Move stations to active runs.
7. Avoid placing bait immediately before or immediately after a rain
storm.
8. Zinc phosphide is not a good repeat bait.
9. Read the label and follow it carefully.
10. Acquire any necessary permits before you apply any type of bait.
-----Original Message-----
From: [email protected] [mailto:[EMAIL PROTECTED]
On Behalf Of Karl Townsend
Sent: Friday, November 09, 2007 4:33 AM
To: Apple-Crop
Subject: Re: Apple-Crop: Mouse Bait
> the orchard. As I recall, it was a bait that was supposedly very
> effective. Does anyone recall that subject? . . . if so, what is the
> name of the stuff, who makes it, & where can I buy it? I've been
> using an anti-coagulant called "Tom Cat" and it just doesn't seem to
> be very effective.
You're most likely thinking of Zinc Phosfide (sp?). ZP is one name, sold as
pellets. provides a quick knock down, bait disolves when wet and mice
quickly get bait shy.
I think a complete approach is needed. Get rid of as much cover as possible.
Use mouse tree guards. Use ZP once/year, late in the season(now). I also
have sheets of old barn roofing steel all around the perimeter of the
orchard. Apply the Tom Cat chunks underneath the steel sheets just before
winter sets in. Then the mice have a nice place to get out of the weather
AND a little to eat <Grin>
Karl
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