The five worst invasive species in South Africa are:
1. Pompom weed (Campuloclinium macrocephalum) – Category 1b
Pompom weed was introduced to South Africa in horse feed (hay) during the Anglo Boer War (1899) that was imported from Brazil and Argentina. The plant is a serious threat to the conservation of grasslands in South Africa. This invader causes serious degradation of the veld, lowering the biodiversity and reducing the grazing capacity by being unpalatable to large herbivores. Infestations become conspicuous when the plants are in flower between December and March, transforming the veld from green to pink.
2. Water hyacinth (Eichhornia crassipes) –
Category 1b
Water hyacinth is one of the world’s worst aquatic weed due to its invasive potential, negative impact on aquatic ecosystems, and the high rate of costs to control it. This invader forms dense mats which completely cover the water surface of dams leading to altered water chemistry and composition to the detriment of other organisms. Negative effects associated with water hyacinth infestation include the destruction of local aquatic biodiversity, the blockade of river flows which may aggravate flooding and interference with water utilization for activities like recreation or irrigation.
3. Famine weed (Parthenium hysterophorus) – Category 1b
This aggressive plant rapidly invades disturbed areas, agricultural land used for crop and animal production, fallow land, roadsides and watercourses, causing severe economic losses and threatening biodiversity.The plant is a known irritant – continuous exposure causes respiratory problems such as hayfever and asthma in humans, as well as allergic contact dermatitis. Cattle that have consumed famine weed are not fit for human consumption and their milk may become toxic.
4. Lantana (Lantana camara) – Category 1b
Lantana camara is a poisonous invader of veld and plantations. It replaces indigenous species. Allelopathic suppression of indigenous species interrupts regenerationprocesses and reduces biodiversity of natural ecosystems. Dense stands in plantations obstruct access and utilization. This plant is poisonous to humans and animals and responsible for livestock mortalities amounting to millions of Rands every year in South Africa. It also reduces the grazing potential of the land.
5. Bugweed (Solanum mauritianum) – Category 1b
Bugweed replaces indigenous riverine and forest margin species. This invader also competes with young trees in plantations, particularly pines and black wattle, inhibiting growth and causing stem deformation. It is a host of the KwaZulu-Natal fruit fly which is an economic pest. It has no fodder value and the plants are generally avoided by grazing animals. The unripe fruits are poisonous and the hairy leaves and stems can cause allergic dermatitis and asthma.
