Baiting Strategies

Because each rodenticide product has a recommended use pattern, professionals need to consider in which situations the various compounds are best used. The single-dose rodenticide zinc phosphide, for example, should be used only at intervals (such as six months) to prevent the development of wide-scale bait shyness.

Each effort should be a maximum one. With these types of baits, it is best to use as many bait placements as possible during several days of baiting and then stop. The professional may decide to shift to alternate rodenticides, if necessary, to kill remaining animals.

With first-generation anticoagulants, an adequate bait supply must be maintained during the entire control period because the rodent must be able to feed daily for a week or more. With some of the first-generation compounds, as many as 10 successive feedings are required. Missing a day cancels the effect of previous feeding. Maintaining such amounts of bait may increase the chances that nontarget species will consume it.

The second-generation anticoagulants have much greater activity with much smaller doses. Thus, relatively small amounts (usually acquired with a single feeding or within one day of feeding) of bait are required to be effective. Unfortunately, it still takes several days for death to occur, and in the meantime, rodents continue feeding.

One method called "pulsed baiting" was proposed and studied by researchers in the early 1980s. The researcher A. Dubock believed that only a single feeding is required to produce a lethal result and can be used as a basis for an efficient baiting regimen in those cases where the professional expects to conduct follow-up visits on a weekly basis. (These should be done with an initial cleanout program against rodent infestations.) Bait initially placed to satisfy the estimated number of rodents should be increased if rodent signs or activity persists. However, bait initially placed will result in death to those rodents that ate it. Similarly, this result will be true of the second (and third) baiting. Thus, the effect of each baiting is maximized.

Not all rodents will come in contact with the bait in the initial placement. Especially with mice, populations may exist in ceilings, attics or other relatively inaccessible sites. Not until the dominant individuals are removed can these other animals expand their ranges and find the bait. Thus, several waves of feeding may occur.

Several different types of rodenticide bait stations are used in the industry. Some are more effective and/or appropriate for use in one type of facility than in another or within certain areas of a facility (e.g. indoor baiting vs. outdoor baiting).

Placing baits in containers offers the advantages of keeping the bait fresh and protected from dirt and moisture, and also reduces the chances of accidental poisoning of people, livestock, pets and nontarget wildlife. It also allows the monitoring of bait consumption and activity in particular areas.

When bait stations are used for elimination and maintenance programs, they should be spaced at 8- to 12-foot intervals for mice, and 25- to 50-foot intervals for rats in areas showing rodent activity. Use closer spacing for severe rodent infestations.