Spiny Emex australis burrs caught in a car tyre.
Biological control of Emex: the weed and potential agents
Emex, an introduced weed that competes with crops and pastures, is a pest across Australia's southern temperate regions.
16 November 2006 | Updated 14 October 2011
Emex australis, doublegee (Western Australia) and three-cornered jack or spiny Emex (eastern states), is originally from South Africa. It was intentionally imported into Western Australia (WA) in 1830 as a vegetable, Cape spinach. Once in Australia, it spread rapidly and now occurs throughout Australia's southern-temperate regions.
An annual weed, it competes with crops and pastures and is estimated to cost A$40 million a year in crop losses/production costs in WA alone. A single plant can produce more than 1 000 burrs which can contaminate agricultural produce such as wool, grain and dried fruit.
Lesser jack (E. spinosa) is also a problem in some areas of southern Australia. It looks similar to E. australis but has more erect stems and smaller burrs.
Seeds from both Emex species can remain dormant in the soil for more than seven years and this dormancy, together with rotational cropping-grazing farm practices, can make controlling them a problem.
Emex is estimated to cost A$40 million a year in crop losses/production costs in WA alone.
Seedlings from both Emex species are selectively and effectively killed by broadleaf herbicides within the crop phase of a cropping-grazing farming system, but seed banks build-up during the pasture phase when suitable herbicides are often not applied.
Many herbicides that control the Emex species also damage other beneficial broadleaf-pasture species and/or the growers are not willing to expend resources on weed control during the non-cropping phase due to lower economic returns in this phase.
These problems led to CSIRO Entomology, in 1974, to begin investigating the possible biological control of E. australis.
Potential biological control agents
The first agent released on Emex was the weevil, Perapion antiquum. Although this species controlled Emex in Hawaii, it did not establish in Australia because of our harsh summers.
A second weevil, Lixus cribricollis, was collected from E. spinosa in Morocco and released in Western Australia in 1981. This species also appears to have not established.
Later studies concentrated on E. spinosa populations in Israel where summer extremes are similar to those in Australia.
Red apion (Apion miniatum) is a potential biological control agent, approved by Australian regulatory bodies for field release in 1998. Despite extensive releases (see red apion in Related Topics) the weevil also did not establish.
Other potential biological control agents such as fungi and weevils, are known from north Africa, but have not been studied to determine their potential for use in Australia.
Two exotic organisms that attack Emex have been found in Australia:
the dock aphid, Brachycaudus rumexicolens
the fungus, Phomopsis emicis.
Laboratory and field studies showed these reduced the amount of dormant seed produced by E. australis.
Read more about the Ecology and management of Australian weeds.