Prospects for biological control of cutleaf mignonette, Reseda lutea (Resedaceae), by Cercospora resedae and other pathogens

Abstract

Four leaf pathogens were screened as biological control agents for the weed Reseda lutea (Resedaceae) in South Australia. Cercospora resedae isolated from Reseda luteola growing in south-eastern Australia produced a maximum damage to R. lutea seedlings of 54% of leaf area damaged at 22°C and 96% of leaf area damaged at 27°C under laboratory test conditions. By contrast, European isolates of C. resedae from both R. lutea and R. luteola produced a maximum of 10% leaf area damage to R. lutea seedlings. Field releases of Australian C. resedae failed to establish in dense populations of R. lutea on Yorke Peninsula and the mid-north of South Australia, perhaps because the climate was hotter and drier than the source locations. Attempts to enhance the effectiveness of the pathogen by passaging it through R. lutea, leaf abrasion, inundation, or the addition of surfactant or sublethal doses of metsulfuron-methyl failed to increase damage beyond that caused by the pathogen alone. The leaf pathogensAlternaria tenuissima, Cladosporium sp. and Peronospora crispula did not produce damage levels that could be useful in biological control. It is concluded that in the areas of South Australia where R. lutea is a significant weed, the prospects for control by any of these leaf pathogens are not good.