out daily for at least 2 weeks to ensure that
the poison is effective.
Anticoagulant rodenticides are commer-
cially available in several forms. They are
sold as ready-to-use baits that can be placed
in plastic or corrugated containers near
rodent runways; in pellet form, mixed with
grain for use in rodent burrows and dead
spaces between walls; in small plastic pack-
ages for placement in rodent hiding places; in
bait blocks; and as salts that are mixed with
water. The sanitarian or pest control opera-
tor should record the location of all bait
containers for easy inspection and replace-
ment. If bait is not consumed after two or
more inspections, it should be relocated.
Anticoagulants have been extensively used
to eradicate rats. One unfortunate result is
that rats have become increasingly resistant
to them. Consequently, new control strate-
gies are being studied that utilize alternative
cycles of anticoagulant and acute (fast-act-
ing) rodenticides. Difathialone, an active
ingredient similar in mode of action to other
second-generation anticoagulants, is effec-
tive at 25 ppm or half of the concentration
of other anticoagulant baits (Corrigan,
2003). Bromethalin, a nonanticoagulant
has been reformulated and remarketed by
two manufacturers since its introduction in
the early 1980s. This rodenticide produces
death in rodents 1 to 3 days compared to 5 to
7 days for anticoagulants, but is approxi-
mately twice as expensive as anticoagulant
baits.
If immediate death of rodents is required,
single-dose (acute) poisons, such as red squill
and zinc phosphide, are available. These poi-
sons can be mixed with fresh bait material,
such as meat, cornmeal, and peanut butter.
These baits should be prepared and adminis-
tered according to directions provided by the
manufacturer. Unfortunately, some of the
single-dose poisons are effective against only
Norway rats.
Baits should be deposited in several loca-
tions because rodents frequently travel only a
limited distance from their shelter. If suffi-
cient food and shelter are available, rats tend
to stay within a radius of 50 m. Mice tend to
journey about 10 m under similar conditions.
If baits are dispersed too sparsely or are not
strategically located, rodents may not locate
the poison. Where signs of rodent activity
are recent and numerous, baits should be dis-
persed liberally and replaced frequently.
Rodents that are killed by single-dose poi-
sons may die in their nests. Dead rodents
should be removed and burned or buried.
Most mice are destroyed from the same com-
pounds as rats.
Although use of bait is one of the most
effective methods of eradication, rats that
have suffered a toxic response by ingesting a
poison, such as discomfort and pain but not
death, may avoid the bait. They also become
cautious if dead or dying rats are near bait.
Therefore, the most acceptable bait is the
type with which the rat is most familiar.
Bait shyness and avoidance may be coun-
tered by the use of prebait, nonpoisoned bait
introduced for approximately 1 week. Then
the prebait is replaced with the same bait
containing a rodenticide. Prebaiting is espe-
cially important if single-dose poisons are
used but is not recommended when antico-
agulants are incorporated. Because mice
have weaker avoidance instincts than rats,
prebaiting for mice is not necessary.Tracking Powder
These compounds kill rats or, in the case
of nontoxic powders, identify their presence
and number. These powders may contain an
anticoagulant or a single-dose poison. This
poison kills rodents when they groom them-
selves after running through the powder.
Such powders are effective if the food supply
is abundant. It is best to use self-contained
bait boxes placed inside the buildings where