Technical Abstract: In Southern Brazil Baccharis coridifolia is an important toxic plant. The poisoning occurs when animals raised in areas without the plant are transported to, and allowed to graze in, pastures infested by B. coridifolia. Intoxication risk increases considerably when recently transported animals are stressed, fatigued, hungry, or thirsty. Farmers prevent B. coridifolia poisoning using several unconventional methods to reduce ingestion: 1) burning plant material under an animals’ nose, and having the animal inhale the resulting smoke; 2) rubbing the plant on the animals’ muzzle and mouth; and 3) gradually introducing animals into B. coridifolia-infested pastures. We studied the aversive plant effect in sheep and tested the empirical methods used by farmers to induced aversion to B. coridifolia to cattle. In Group 1 four sheep ingested 0.25 g/kg bw of fresh B. coridifolia. In Group 2, four sheep were treated by rubbing the plant in the mouth. In Group 3, four sheep inhaled smoke produced by burning B. coridifolia. In Group 4, two sheep were treated by oral gavage with 175 mg/kg lithium chloride. In Group 5, two sheep received alfalfa by oral gavage. In Group 6, two sheep inhaled the smoke produced by burning ryegrass. Results demonstrate that B. coridifolia is as efficient as LiCl in conditioning an aversion to a previously unknown food. It was concluded that the administration of 25% of a lethal dose of B. coridifolia to cattle induces strong aversion to the plant and prevents poisoning if the animals are introduced at least 24 hours after treatment in paddocks with 20% of forage as Baccharis.