 From
"Midwest Tree Fruit Spray Guide 2003," mice (more specifically
known as voles) can cause serious damage to fruit plantings. Frequently,
damage occurs but is not noticed until trees become weak, die or are
removed. Damage can be anticipated each year, particularly from late
summer to early spring, as they eat bark from the base of small saplings.
Such damage can result in girdling death of the tree. Apple trees
are most susceptible, but hungry voles will attack other fruit trees.
Apple trees on dwarfing root stocks are particularly palatable to
these mice.
Many
plantings are being made in a hedgerow pattern; this does not permit
cultivation between trees. Such plantings favor vole migration,
as do mulches and vigorous sods. High populations also favor vole
migrations. No single material or technique is effective for complete
control of voles. It is therefore suggested that both the materials
and the methods of control be varied during the season.
General
Orchard Management Practices
A number of general orchard management practices can be employed
to reduce the risk of injury and improve the effectiveness of control
programs. Tree guards can be constructed from “hardware cloth”
or similar materials with no larger than 1/4 inch mesh. These guards
should enclose the tree and extend from several inches below the
soil surface (voles dig in the top 2-3 inches of soil) to several
inches above maximum snow line (about 18 inches). Pea-sized gravel
or cinders, when placed around the trees, 4-6 inches wide and deep,
also tend to discourage meadow voles from attacking the crown of
the tree, but do not discourage other mouse species. To proliferate,
voles must have abundant amounts of cover. Thus, maintaining a clean
area 1 to 2 feet wide around the base of the trunk of the tree discourages
surface feeding. This will also regulate vole populations in the
long term. Chemical weed control in early spring significantly reduces
the amount of labor involved in keeping the area around the tree
clean.
The
orchard cover or sod should be mowed short in late August and again
after harvest. This reduces runway cover and aids baiting procedures.
Cleaning out drainage ditches and fence rows, as well as either
picking up or crushing all dropped fruit, discourages large mouse
populations.
Orchard
Mouse Control Program
Essential Knowledge
Determine species of vole (with snap traps). Three species may be
found: Meadow Mouse (Microtus pennsylvanicus), Prairie
Mouse (Microtus ochrogaster), Pine Mouse (Pitymys pinetorum).
Materials for control may be the same, but control methods differ.
Quick field identification may be made for both juveniles and adults
based on the length of the tail.
-
Pine Vole: tail length about same length as the length
of the hind foot.
- Meadow
and Prairie Vole: tail length about twice the length of the
hind foot.
- Determine
infestations (with snap traps). There is a definite advantage
in knowing when and where mice are most abundant. This makes control
easier
Control
Control of mice in orchards can be accomplished using either zinc
phosphide or chlorophacinone baits. Both baits will provide good
control if used according to label directions.
Zinc
phosphide is considered an acute bait and causes death of mice within
24 hours. It is available as either a weather-resistant pellet bait
or mixed with prepared grains such as oats and corn. It is usually
well accepted by mice. Zinc phosphide is not effective if applied
more than two times.
Chlorophacinone
(e.g.,RoZol ™) is an anticoagulant bait also available in
some states (check your state regulations) as a weather-resistant
pellet style bait. This bait is highly accepted by rodents, but
death does not occur for several days. For effective control, a
second application of chlorophacinone is needed within 20 to 40
days.
In
general, all baits can be attractive to other wildlife including
some birds and to domestic pets as well. Care must be taken that
bait is applied directly in runs, bait stations (see below), or
broadcast. Pick up all spilled materials to avoid consumption by
non-target animals
Effectiveness
of baits against meadow and pine voles
Chlorophacinone is more effective against pine vole than meadow
vole, while zinc phosphide is more effective against meadow vole
than pine vole. Consistent use of one of these chemicals will result
in a shift of the vole population from one species to the other;
therefore alternate baiting using zinc phosphide in the first application
followed by chlorophacinone in the second application will likely
reduce the populations of both species.
Techniques
for Baiting
-
Machine baiting: Expose bait in artificial trail (Trail Builder)
-
Trail baiting: Expose bait in natural active runways only.
Broadcast baiting: (NOT RECOMMENDED FOR PINE VOLE CONTROL). Broadcast
bait by hand, cyclone type seeder, or tractor drawn equipment
at recommended rates. When using zinc phosphide baits, the 2%
concentration is recommended. OBSERVE SAFETY PRECAUTIONS. Zinc
phosphide is a restricted use material. Read and follow
all label directions and precautions.
Percentage
Comparison of Control Methods
Method |
Meadow
or Prairie Voles |
Pine
Voles |
Machine |
90-95% |
80-85% |
Trail |
80-85% |
70-75% |
Broadcast |
78% |
Not
recommended |
Timing
Apply on a sunny day in late fall when the mice are active. Mice
begin to build up in early August, but baiting should be delayed
to as late as possible in the fall. The most effective period for
application is just before snow cover, after the grass cover has
been reduced by frost, and when the fruit is rotted. Spot treatment
during the winter and into early spring is recommended. Treat marginal
lands to prevent re-invasion.
Pre-harvest
Baiting Is Not Recommended
Application of poisoned bait before harvest to prevent orchard mouse
damage to fruit in cold storage is not a sound practice for the
following reasons:
-
The recommended methods of orchard mouse control do not always
result in 100 percent control of the species in the orchard. Therefore,
some mice survive the pre-harvest control and may enter into the
boxes of fruit on the ground and still be carried into the cold
storage.
-
The pre-harvest poison application will reduce the population
of mice in the orchard; competition among the survivors will be
greatly reduced, and food and cover will be more than ample. The
survivors, under these favorable conditions, will breed and the
number of young per litter may be as high as eight. In a very
short time, the population will recover to its original level.
A large number of young mice will be present during the recovery
period. These mice, having a short home range, would not be exposed
to poisoned baits applied during the normal control season.
-
The recommended control season is just prior to freezing conditions.
This is the best time to control the mice in an orchard and prevent
their damage during the winter months, the season when population
recovery is slowest.
Check your control program with snap traps. Lack of visible
damage does not indicate the effectiveness of your program.
Control
in Storage
-
Before Harvest
a) Poison rats and mice in storage one month before picking; keep
storage area baited, and free of debris.
b) Clean up all outside debris, especially near loading door,
one week before picking.
c) Rodent-proof storage, seal all holes and cracks. Mice can fit
through a hole the size of a dime.
-
During Harvest
a) Move filled boxes into storage quickly as any left overnight
may have mice in them.
b) AS YOU LOAD fruit into storage, bait storage. Place teaspoonful
amounts in bait stations on floor along alleys, between rows of
boxes, and under pallets. Do not place open baits on floors or
any areas where contamination might occur. Commercial bait stations
are available from agricultural supply companies. Always prevent
contact with fruit.
Bait
Stations in the Orchard
Bait stations can be prepared in several ways and eliminate or reduce
the opportunity for non-target animals to contact the bait. Squares
of heavy roofing shingles or other weather-resistant materials placed
out of traffic areas between trees can serve as bait stations to
provide protection for the bait and hiding places for the rodents.
Some growers have constructed bait stations that require less refilling
by building inverted T-shaped stations from PVC tubing and fittings
that will provide bait storage and a protected feeding area. Place
bait stations in the field 2 to 3 weeks before adding the bait. |
