River red gum, a native of Australia, is valued in South Africa as a shade tree, ornamental and street tree, as well as for its ability to survive cold and drought. Together with other gum species, it is a crucial source of pollen and nectar that supports honeybees, which act as the major pollinators of deciduous fruit, vegetable seed crops, subtropical fruit, nuts, oilseeds and berries. Due to its branched shape, however, it is no longer planted as a timber tree. Despite its beneficial qualities, river red gum is highly invasive in riverine situations, where dense stands damage river banks, choke water courses and evaporate excessive amounts of water. 

In terms of the Alien and Invasive Species Regulations (AIS), National Environmental Management: Biodiversity Act (Act No 10 of 2004), river red gum has been declared a category 1b species within the Fynbos, Grassland, Savanna, Albany Thicket, Forest and Indian Ocean Coastal Belt biomes. Its category 1b status necessitates its control or removal and destruction if possible, and no trade or planting is allowed. As a concession to those who depend on its utilization, it is not listed as an invasive within the Nama-Karoo, Succulent Karoo and Desert biomes, nor within cultivated land that is at least 50 metres away from untransformed land, nor within 50 metres of the main house on a farm, nor large trees (diameter >400 mm) growing in urban areas, except if they grow in riparian areas, declared protected areas, listed ecosystems or ecosystems identified for conservation, where the gum will still be regarded as a category 1b species.  All river red gums used in plantations, woodlots, bee-forage areas, wind-rows and the lining of avenues (excluding those in the exempted biomes mentioned above) are declared as category 2 species. This means that land managers have to apply for a permit to carry out a restricted activity (such as having, growing, breeding or propagating the trees or allowing them to spread) in a demarcated area. Enquiries regarding permits can be addressed to AISpermits@environment.gov.za.

Trees whose removal is required by law, can be ring-barked, and for the sake of safety the dead trees should preferably be felled before they fall over. Instead of killing the trees in this way, land users might make use of a contractor linked to a Government initiative to make school desks for marginalized communities from invasive trees; contact info@invasives.org.za​.  

Research, using funding from the Working for Water Programme (DEA:NRMP), was carried out to investigate the possibility of using host-specific organisms to prevent seed production in river red gum. It was hoped that such organisms would reduce the invasive potential of the gums, while still allowing the utilization of the trees, even by honeybees. The outcome of the research was that a chalcid wasp, Quadrastichodella nova, which must have entered the country from Australia with seeds imported for afforestation, is already producing galls within the seed capsules of river red gum in South Africa. These galls have the potential to severely limit the number of seeds in affected seed capsules, but the gall-inducer is heavily parasitized by several wasp species that are also thought to have arrived from Australia. It seems unlikely that there would be room for another seed-reducing biocontrol agent for river red gum in South Africa, and no more research into this subject is currently underway.

• Quadrastichodella nova and its gall associates

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