Horehound (Marrubium vulgare):a comparison between European and Australian populations
John Weiss and Jean-Louis SaglioccoA, Keith Turnbull Research Institute, Victorian Department of Natural Resources and Environment, CRC for Weed Management Systems, PO Box 48, Frankston, Victoria 3199, Australia.
A Previous address: CSIRO European Laboratory, Campus International de Baillarguet, 34980 Montferrier sur Lez, Cedex, France.
Horehound (Marrubium vulgare L.), a noxious weed throughout southern Australia, was imported from its native southern Europe during the 1800s. Horehound in its native habitat shows weed potential, but is scattered and occurs in less dense infestations than in Australian infestations where the plant is larger and more vigorous. The seed production and seed bank studies indicate that there is at least a one hundred-fold difference between the two populations. At Victorian infestations, either space or water appear to be the limiting factor affecting survival and recruitment while sustained herbivory pressure restricts horehound in its native range. Climate modelling based on overseas populations indicates that horehound in Australia maybe close to achieving its full distribution.
The insect fauna of horehound has been examined and a total of twenty-eight insects have been found feeding on the plant in Mediterranean Europe. In comparison only a couple of oligophagous insects are on horehound in Australia and in consequence four European insects have been identified as suitable agents for biological control. Two of these have been approved and released into the Australian environment.
Plant Protection Quarterly (2000) 15 (1) 18-20.