Emex australis Steinheil – doublegee

Emex australis and Emex spinosa (Polygonaceae) are annual winter-growing herbs. E. australis, doublegee, originates from southern Africa and is widespread across southern Australia where it is a weed of crops and pasture. E. spinosa, lesser jack, is native to the coastal areas of several countries bordering the Mediterranean Sea. In Australia, distribution of E. spinosa has remained restricted to a few locations and it has less impact on crops than E. australis. Consequently, Australian biocontrol projects have primarily targeted E. australis. A South African weevil, Perapion antiquum, was successful in controlling Emex in parts of Hawaii. However, when released in Australia it failed to establish at most locations and had no beneficial impact. Other natural enemies found on E. australis in South Africa were either not suitably host-specific or were already present as accidental introductions to Australia. An example of the latter is the widely established fungus Phomopsis emicis that reduces seed survival in E. australis. To expand the list of potential biocontrol agents for E. australis, surveys for pathogens and invertebrates were conducted on Mediterranean populations of E. spinosa. Two weevils, Apion frumentarium and Lixus linearis, attack both Emex species and were approved for release in Australia, but both failed to establish. A northern hemisphere aphid, Brachycaudus rumexicolens, that was not part of the biocontrol program, appeared in Australia in 1985. It spread naturally across southern Australia and under favourable climatic conditions can have a severe effect on Emex. Priority organisms for future study include the weevil Perapion neofallax because of its ability to diapause over summer, and the pathogen Cercospora tripolitana. Both originate from E. spinosa in North Africa. Any future biocontrol project will need to take into account the use of Emex seeds as a food source by native birds and the risk to native Rumex species, as well as an assessment of the continuing importance of Emex species due to changing agronomic practices.