Field trials of difenacoum against warfarin-resistant infestations of Rattus norvegicus.

The anticoagulant difenacoum was tested at two concentrations, 0-005 and 0-01%, in bait against warfarin-resistant rat infestations in farm buildings. Twelve out of the 14 treatments in which the lower concentration of the anticoagulant was used resulted in complete control. One of the remaining two treatments was probably also completely successful, but in the other a few rats, that were not eating the poisoned baits, were still active after 30 days of baiting. All six treatments done using the stronger concentration of poison were completely effective. Since it took as long to control infestations with 0.01% as with 0.005% difenacoum in treatments carried out under similar conditions, the lower concentration is recommended for use against warfarin-resistant rats.