precautions should be taken to prevent humans, domestic animals, and pets from
eating baits containing anticoagulants. These chemicals are stable and are odorless
and tasteless to rodents in the concentrations used. A single feeding on bait containing
an anticoagulant at the recommended concentration is not sufficient to cause death.
Food baits or water solutions must be consumed over a period of several days before
they become effective. Even when weakened, rats and mice do not associate their loss
of strength with their food supply. This means that the problem of bait shyness
commonly associated with "one-shot" poisons is largely overcome. Maximum kill is
generally achieved between the fourth and ninth nights that poisoned bait is consumed
by the rodent. Continuous baiting for two weeks (or longer) is often required to obtain
satisfactory control. To control house mouse populations, continuous baiting for a
month or more may be necessary because of the nibbling habits of mice. Bait should
be placed in a bait station or in a place that offers the rodent a protected feeding place
and protects the bait from domestic animals and the weather. Spoiling of the bait
material will, of course, depend on the type of food used and on climatic conditions. Dry
cereal baits remain in good condition much longer than meat or vegetable baits and are,
therefore, the foods of choice for use with anticoagulants. Baits should be replenished
before they are completely eaten to prevent the rodents from abandoning the feeding
stations and to prevent infestation by stored products pests. Anticoagulants are
provided in two formulations -- a prepared material, ready for use, and concentrated for
use in the preparation of food baits or water solutions. The active ingredient may be
one of the following chemicals: Diphacinone, Warfarin, Fumarin, Pival, or PMP.
a. Rodenticide, Anticoagulant, Ready Mixed. This formulation is a
ready-to-use bait containing an anticoagulant chemical, rolled oats, sugar, and mineral
oil (to increase its acceptability). A red dye has been added to distinguish it from
ordinary rolled oats. The item is used directly from its container without further mixing.
b. Rodenticide, Anticoagulant, Universal Concentrate. This item is a
concentrate that can be mixed with food, bait, or water. It consists of a warm soluble
anticoagulant chemical, sugar (to make water solutions more palatable), sodium
benzoate (a preservative), and a complexing agent to hold the anticoagulant in solution.
Glass, plastic, or paper water-holding containers may be used for dispensing. Poisoned
water is especially effective where water is scarce. The use of poisoned water and
poisoned baits simultaneously will increase the effectiveness of the control program.
1-10. ZINC PHOSPHIDE
Zinc phosphide is a highly poisonous black powder consisting of about 75
percent zinc phosphide and 25 percent antimony-potassium tartrate. The latter
compound is an emetic that has been added to prevent accidental poisoning of humans
and domestic animals. One feeding of poisoned bait containing 0.1 percent zinc
phosphide is sufficient to kill a rodent. A single sublethal dose can cause bait shyness
for baits containing this poison. Therefore, an acceptable food must be used as bait to
achieve successful control. Although zinc phosphide has a disagreeable odor to
humans, it is not repellent to rats and may even attract them.