Integration of herbicide treatments with the plume moth for horehound control
N. Ainsworth and C. Morris, Keith Turnbull Research Institute, Victorian Department of Natural Resources and Environment, CRC for Weed Management Systems, PO Box 48, Frankston, Victoria 3199, Australia.
The plume moth Wheeleria spilodactylus (Curtis) is becoming widespread and demonstrating a useful impact on horehound Marrubium vulgare L. There are circumstances in which herbicide may be used to control horehound when W. spilodactylus is present and there is a need for more information on how the biological control agent may respond to herbicide if the outcome of these treatments is to be predicted. Herbicide applied to M. vulgare will prevent flowering for some time even if the plant is not killed. Previous work found that lack of M. vulgare flowers to feed on significantly shortened the lifespan of adult W. spilodactylus.
The present study confirms this finding and shows that flowers of other species are not of any benefit in increasing the lifespan of W. spilodactylus that are deprived of M. vulgare flowers. Another important question is whether adult female W. spilodactylus will avoid herbicide sprayed M. vulgare, in favour of untreated plants several metres away, when selecting oviposition sites. Four separate trials at different times after herbicide application found that by three or four weeks after herbicide was applied female W. spilodactylus released on herbicide treated plants did move within a few days to adjacent untreated plants. The findings are discussed in relation to potential effects of herbicide treatment on population size and impact of W. spilodactylus in the field after herbicide is applied in different ways.
Plant Protection Quarterly (2000) 15 (1) 37-39.