October 2021 - 32

WILDLIFE & RODENT MANAGEMENT
Controlling rodent pests in the orchard
By Crystal Nay
Western Editor
In addition to insect pests and
disease, rodents and other wildlife can
be pests in the orchard, causing various
degrees of damage to both plants and
equipment. Survey data collected in
the 2010s in cropping systems, which
included nuts, revealed an 8.7% loss
in revenue when ground squirrels are
present, 6.1% from pocket gophers due
to tree mortality since they don't feed
on nuts, 9.6% loss from birds and 4.2%
from voles.
There are other critters as well who
like to cause problems in the orchard.
Coyotes, rabbits, rats and others will
sometimes chew irrigation lines, and
raccoons and opossums might find a
tasty snack up in the tree and cause
some damage, but these are more
localized incidents.
Rodents, however, tend to take the
lead.
Vulnerability of young trees
As if there weren't a myriad of other
things to worry about when establishing
new trees, wildlife pests are another
concern. Both rabbits and voles can
girdle young trees, but become less of a
problem when trees reach 4-5 years.
Voles, however, can be particularly
damaging to newly planted trees,
especially those with cover crops. Voles
are very cover dependent, so fields with
new trees and either an unmanaged
cover or a lot of weed growth provide
plenty of food and shelter for a critter
that can multiply extremely quickly.
" They can have a new litter every
month, basically, and those litters can
have their own litter after a month, " said
Vole by a tree. Photos: Roger Baldwin.
Roger Baldwin, Extension specialist
with University of California, Davis,
specializing in human-wildlife conflict
resolution. " And if a grower creates a
perfect environment for them, those
populations have the ability to explode. "
Also targeting young trees are pocket
gophers, which spend most of their time
below ground, girdling the trees below
ground level and consuming the roots.
Above ground damage can be
extensive, but burrowing rodents
can cause more damage beneath the
ground, such as redirecting water,
increasing soil erosion, damaging
farm equipment, posing a risk to
Ground squirrel at a bait station in an
almond orchard. Photo: Roger Baldwin
Knowing a pest's behaviors can help with targeting them. Some control measures
are more effective during specific parts of the year based on the activities of the pest,
as illustrated here with the California ground squirrel. Graph: University of California
Agriculture and Natural Resources
farmworkers, and chewing on and
damaging tree roots.
Transforming habitat
Each rodent situation is different, and
a site assessment can help determine the
most effective way to transform habitat
in order to prevent further damage.
However, habitat transformation works to
varying degrees for all the rodent species.
One example of where habitat
transformation is very effective is with
voles. Since they are cover dependent, a
good way to prevent damage to trees is by
removing any vegetation from around the
base of the tree, and by mowing any cover
to within a couple of inches of stubble
height or less.
" For other species, it's a little more hit
and miss, " said Baldwin.
For a lot of rodent species, decadent
growth or old, weedy cover around the
orchard can become a preferred habitat,
in which rodent pests will stay before
moving into other areas and causing
damage. Things like brush and pruning
piles that are left along the edge of an
orchard create shelter for a variety of
different species, which will then come
out at night and feed on the trees. Or,
in the case of ground squirrels, during
the day.
20 | FruitGrowersNews.com
http://www.FruitGrowersNews.com
October 2021

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