Sheep as a biological control agent for tansy ragwort

Abstract

Tansy ragwort (Senecio jacobaea) is a biennial weed commonly found on forest and pasture lands in the maritime regions of the Pacific Northwest. Pyrrolizidine alkaloids in tansy ragwort, when consumed by most types of livestock, produce progressive and irreversible liver damage. Sheep, however, appear immune to these alkaloids. To evaluate the possibility of using sheep to suppress tansy ragwort in cattle pastures, 100 plants were marked and their status followed during 1977 and 1978 in pastures grazed by cattle alone and in pastures grazed by both cattle and sheep. Total tansy ragwort mortality did not differ between pastures. However, the cause of mortality did differ. Mortality on the cattle-grazed pasture was predominately due to completion of the plant's biennial life cycle (blooming and seed set), while most plant mortality on the sheep plus cattle pasture appeared to be the result of grazing. The data suggest that sheep may be used as a biological control agent to suppress tansy ragwort populations by reducing their ability to produce seed.