Invertebrate and fungal associations of the pastoral weed, Madagascar ragwort, Senecio madagascariensis Poir, in Northland, New Zealand, and implications for biocontrol

Abstract

ABSTRACT Senecio madagascariensis Poir is now found in New Zealand colonising pastoral habitats north of a latitude 35.5°S. This prolific, continuous flowering, toxic perennial weed may not have reached its potential geographic range in New Zealand and is poorly controlled by herbicides. Prior to embarking on a biocontrol programme for this weed, we present a survey of invertebrates and diseases which found relatively few natural enemies and no specialised herbivores or plant pathogens in its current range in New Zealand. The most significant herbivorous insect pests were Hemipteran sap-suckers from 8 families. Percentage infestation of seedheads by the multivoltine tephritid fly, Sphenella rufriceps (Macquart) ranged from 16.7% to 49.8%. Fewer stems of S. madagascariensis were found in plants infected by the fungus, Puccinia lagenophorae Cooke. A search in Western Province (RSA) and in Madagascar for biocontrol control agents host specific to S. madagascariensis is planned.