Background

What is the weed problem?

Sea spurge is a significant environmental weed of coastal dune ecosystems in southern Australia. Re-invasion from ocean-dispersed seed is a constant threat to achieving long-term control. Along the NSW South Coast, sea spurge keeps re-invading sand dunes and is progressively moving northward. Infestations of sea spurge can negatively affect threatened flora and fauna species and Aboriginal cultural heritage sites, alter the geomorphic processes on the coast, transform native vegetation communities and reduce public amenity in coastal recreation areas. Sea spurge can also cause skin and eye irritations in those who inadvertently touch its milky latex sap. Each plant can produce up to 5000 seeds that can survive for several years on ocean currents – the primary means of dissemination from beach to beach.

How is the weed currently managed?

Control of sea spurge infestations with manual and chemical control techniques is difficult because of the close proximity to estuaries, the marine environment and native vegetation, its persistent seed banks, and constant re-invasion from beaches within and outside of NSW. Government agencies and local community groups devote large amount of time controlling it, but ongoing efforts are required because of the established seed bank and the relentless re-invasion that occurs.

Hand pulling of sea spurge is popular with community groups, as it requires no special training, costs little, and avoids exposing community members to chemical herbicides. It can be quite effective for small populations less than a few thousand individuals. The incomplete removal of the plants’ roots however, can lead to their re-establishment. Even when plants are completely removed, recruitment of seedlings from the seed bank can occur for up to ten years. The application of herbicides is popular with land management agencies (parks, local councils or NRM organisations). While often effective in reducing large populations of sea spurge, herbicides can cause off-target damage to sensitive native coastal vegetation and aquatic and marine ecosystems.

What can biocontrol offer to the weed’s management?

The hardiness, mobility and longevity of sea spurge’s seeds in combination with the remote locations of many infestations, make management of sea spurge in southern Australia difficult using currently available control methods. Biological control would provide a sustainable, landscape scale approach for sea spurge management with no chance of off-target damage. A successful biocontrol program across the range of sea spurge in Australia would reduce the density of populations and seed production, thus reducing spread via ocean currents and infestation of new beaches. A substantial improvement of biodiversity outcomes would be expected from a progressive reduction of the number of beaches invaded by sea spurge as a result of biocontrol and the commensurate recovery of dune habitats for native flora and fauna.

Previous research (pre-2017)

Due to its importance as an environmental weed, sea spurge was nominated and endorsed by the national Invasive Plants and Animals Committee (IPAC; now known as the Environment and Invasives Committee) as a target for biological control in Australia in August 2010.

In previous projects supported by the Tasmanian government and the Rural Industries Research and Development Corporation (RIRDC; now known as Agrifutures Australia), two damaging fungi with potential for biocontrol – the foliar blight fungus Venturia paralias (previously referred to as Passalora euphorbiae) and the rust fungus Melampsora euphorbiae – were discovered on sea spurge during field surveys in France and Spain. Initial tests, performed at the CSIRO European Laboratory in France, indicated that the two pathogens may be promising candidate biocontrol agents for sea spurge in Australia (Scott et al. 2010, 2012). Out of 15 non-target species tested with the rust fungus, only Euphorbia marginata and E. dendroides developed disease symptoms, albeit not as severe as those on sea spurge. Preliminary testing with the fungus showed that it is possibly highly specific. It was tested on eight Euphorbia species, but none were native to Australia. It was also tested on two species in the sub-family Acalyphoideae and one species in a related family to Euphorbiaceae. In all tests, disease symptoms only developed on sea spurge. The damage caused by the fungus on sea spurge in the field is impressive in the native range (M. Jourdan pers. comm.).

Baseline data on  sea spurge growth, phenology and reproductive output, and impact on native vegetation were gathered in 2011-12 at sites in WA and Victoria (Scott et al. 2012). A recent Honours thesis at Wollongong University (Kelly 2015), indicated that sea spurge is or has been present at 309 of the 481 beaches (64.2%) assessed in NSW based on information gathered from land managers, management documents and field surveys.

Kelly LJM (2015) Patterns of sea spurge (Euphorbia paralias) invasion in New South Wales, Australia. Honours Thesis, The University of Wollongong.

Scott JK, Jourdan M, Morin L, Thomann T, Yeoh P (2010) Exploration for potential biological control agents of Euphorbia paralias, a major environmental weed of coastal ecosystems in Australia. In: Proceedings of the 17th Australasian Weeds Conference, (ed. Zydenbos SM), pp. 223-226. New Zealand Plant Protection Society Inc., Christchurch. http://caws.nzpps.org/awc/2010/awc201012231.pdf

Scott JK, Jourdan M, Morin L, Webber BL, Yeoh PB, Ebeling SK, Cousens R (2012) Sea spurge, Euphorbia paralias, ecological assessment and testing of potential biological control agents. In: Proceedings of the 18th Australasian Weeds Conference, (ed. Eldershaw V), pp. 223-226. Weed Society of Victoria Inc., Melbourne. http://caws.nzpps.org/awc/2012/awc201213751.pdf