MYCOHERBICIDES AND OTHER BIOCONTROL AGENTS FOR SENECIO SPP

Classical biocontrol of Senecio jacobaea (ragwort) has generally utili sed herbivorous insects, although the rust Puccinia expansa has also b een considered. Although this rust is specific and damaging in the gla sshouse, it has not been used in the field. Research into the ecophysi ology of Senecio vulgaris (groundsel) infected by the rust Puccinia la genophorae has revealed the extent to which the effects of infection a re dependent on environmental factors. The damage caused by rust is en hanced under mild drought conditions, during periods of frost in winte r and by competition between groundsel and neighbouring plants, but is reduced by nutrient deficiency. Rust injury is also greatly increased by secondary infection of pustules by necrotrophic fungi. Such second ary infection can be achieved artificially with a range of opportunist ic necrotrophs and can selectively kill groundsel: the effective inocu lum dose of both fungi is significantly reduced. Attempts to apply our understanding of rust-necrotroph injury to ragwort have been partiall y successful but we have not succeeded in causing significant mortalit y of this host. This paper discusses these, and other weed-pathogen-en vironment interactions, and their possible application to biocontrol.