Norbormide at 1·0 and 0·5% and zinc phosphide at 5·0 and 2·5% were each tested in four types of cereal bait, after prebaiting and as direct poisons, against infestations of R. norvegicus on forty-eight farms in Montgomeryshire.
The relative success of treatments was measured by the reduction in the number of takes from wheat baits put down for 2 days, 13 or 16 days before, and 5 days after, poisoning.
Treatments with zinc phosphide were significantly more successful than those with norbormide, irrespective of the cereal bait, concentration of poison or method of treatment used, and in spite of conditions on many farms that partially restricted the distribution of the baits containing zinc phosphide.
Differences between these results and results of laboratory tests with the same rodenticides are discussed.
Norbormide is recommended for use in situations where zinc phosphide cannot be used efficiently without risk to livestock.
We are indebted to Messrs Tavolek Laboratories Limited, Slough, for the free supply of norbormide made available early in the trial; also to Messrs. Lloyd and Pritchard, who were responsible for all the treatments; to Miss E. J. Taylor and Miss P. Cullen for assistance with some of the census baiting, and to J. H. Greaves for permission to examine original data and present them in Table 3.