Management of the invasive cord grass, Spartina alterniflora, in the Groot Brak Estuary: challenges and progress
Ernita van Wyk1, David G. Harding2, Virgil Jacobs1, Nolwethu Jubase1, Janine Adams3, Taryn Riddin3
1Invasive Species Programme, SANBI; 2Invader Plant Specialists; 3Department of Botany, Nelson Mandela Metropolitan University
Spartina alterniflora is an invasive cord grass native to the Atlantic and Gulf Coasts of North America. The species is adapted to living in salt marshes and estuaries and was found growing in the Groot Brak estuary between Mossel Bay and George in 2004. Research shows that, if left unmanaged, the population in the Groot Brak estuary can spread at a rate 0.162 ha per year, with the possibility of covering 41% of the total vlei area. Currently, the plant occupies less than one hectare of the intertidal marsh. Experiences from Washington State (USA) suggest that small populations of this species can be eradicated. Despite the potential for eradication in the Groot Brak estuary, management of the species in a seasonally open-closed estuary is challenging as natural estuarine conditions create limited windows of opportunity for access and treatment. Foliar herbicide application has proved to be the most effective treatment on S. alterniflora in the Groot Brak system. Following on initial research done on this population by the Nelson Mandela Metropolitan University (NMMU), we set out to discover whether we can control or even eradicate the Groot Brak population. We present preliminary results based on herbicide treatments and on-site population monitoring conducted between 2009 and May 2014. In addition, we present results from an aerial photography exercise applied to this S. alterniflora population to demonstrate the potential value of this method as a monitoring tool.