The lebbeck tree can easily be mistaken for one of our indigenous acacias as it superficially looks like many indigenous trees. Planted as an ornamental, this tree has spread from urban areas to natural coastal forests and bush. It grows 15 metres in height.
The climate in KwaZulu-Natal is favourable to this tree as it originates from tropical Asia. Exotic trees with invasive tendencies mean that they will eventually outcompete indigenous trees and over time will alter the biological integrity of a given ecosystem.
Scented agrimony was cultivated for medicinal use but has jumped the fence and invades wetlands, streams and riverbanks. Over time when the plant is widespread it competes with indigenous plants.
It is an erect, perennial herb reaching slightly over a metre in height. It has deeply toothed leaves which are somewhat rough in texture. If found growing in your garden dispose of it responsible and do not dump it into waste fill sites as it can continue to spread.
The long-leaved wattle was imported for dune stabilisation and for wood but is highly invasive and forms dense stands. Two biological control agents are used to manage the spread of this tree. Melanterius ventralis is a seed-feeding beetle and Trichologaster acaciaelongifoliae is a bud-galling wasp.
Biocontrol agents are effective in reducing the seed production of plants thereby slowing down their spread. Other means of control such as mechanical removal are required to effectively limit the spread of invasive trees and shrubs. Wattle contribute to intense fires in the fynbos biome and alter grasslands.
Pepper tree wattle
The peppertree wattle is a large evergreen tree reaching 20 metres high with a broad, spreading canopy. It invades forests, fynbos and grasslands. It was cultivated as an ornamental and shade tree and often planted on pavements but must now be removed and destroyed.
This tree, like many of the Australian wattles, poses a threat to South Africa’s unique fynbos ecosystem and adds to the fuel load of fires.
Parrot’s feather disrupts natural aquatic processes and impacts on water quality. It can completely cover the surface area of water. This may alter aquatic food webs and in turn impact negatively on indigenous fish species. A beetle in the genus Lysathia is used as a biocontrol agent to control the spread of this aquatic fern.
Cat's Claw Creeper
A prolific climbing and creeping plant that covers and smothers trees and shrubs. It also anchors and grows up the sides of buildings and walls, as well as communications and electric poles where it can damage infrastructure.
Smelter’s bush is a semi-herbaceous annual plant which reaches one metre in height. It thrives along roadsides and drainage lines but will also infiltrate wetlands and other damp localities. However, they do tolerate relatively dry areas and this weed is prolific around towns like Kimberley in the Northern Cape and Thabazimbi in Limpopo Province.
Patricia Duncan is undertaking a PhD research project on Paterson’s Curse. She needs to know what you think about his plant. Help her out and fill in the 15-minute online survey questionnaire at https://tinyurl.com/patersonscurse
Paterson’s Curse (Patterson’s curse) comes from the Mediterranean region of Europe and is a well-publicised agricultural weed in Australia. It is thought to have arrived in Cape Town during a pit-stop of a vessel from the UK destined for Australia during the late 1700s. These vessels often carried livestock and feed which may have been contaminated with Paterson’s curse seeds.
Yellow oleander is a popular garden ornamental, but it is classified as a Category 1b invasive plant, and therefore must be removed and destroyed. The seeds are particularly toxic, but all parts of the plant are poisonous and therefore a hazard to livestock, wild animals and people.
Yellow flag iris
Yellow flag was introduced as a garden pond ornamental, but it is highly invasive and quickly overwhelms sedges and reeds bordering rivers, dams and ponds. It produces seeds inside three-angled capsules. The plant spreads through seed dispersal and spreading rhizomes. Never dump garden refuse or plant fragments alongside wetlands and always use a designated waste site.