A study of the persistence of warfarin on wheat bait used for the control of grey squirrels (Sciurus carolinensis)

Abstract

SUMMARYWheat was treated with 14C‐warfarin sodium (0–02%, w/v. a.i.) using the recommended method for preparing bait for the control of grey squirrels (Sciurus carolinesis L.). The persistence of this anticoagulant on sterilised grain was determined by monitoring the rate of change of radioactivity in five different treatments. The time taken for the initial concentration of warfarin to decrease by half in the samples buried in three forests with different soil types varied between 9 and 60 days, and appeared to be correlated with the soil conditions and rainfall. Wheat kept in a hopper exposed to the weather showed no loss of warfarin during the 12 month study period, although warfarin was lost from a pile of bait left exposed on the soil surface.A sixth radioactive treatment involved normal wheat (as purchased from a merchant) since most squirrel control work is done with unsterilised wheat. This showed that during the summer months when squirrel control is permitted the buried unsterilised wheat germinated, but there was no detectable radioactivity in the shoots. Warfarin was lost from both sterilised and unsterilised grain at similar rates when buried in the same forest.