BIOECONOMIC MODEL OF WEEDS IN PASTURES

Interactions between weeds, pastures and grazing animals are reviewed. It is argued that the economic interpretation of effects of weeds should be based on a farm unit. The weed, Silybum marianum, is examined in relation to a specific farming system. Within a wholefarm framework, two of its effects, competition and reduction of accessibility of pasture, are assessed using hypothetical data. Quantitative data on the physical effects of a weed are shown to provide only a modest indication of the economic consequences of weed infestations on farms. This is due to variable pasture value, management options and carryover feed effects. © 1979.