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Removing alien invasives


JOHANNESBURG City Parks and Zoo are removing invasive alien plants in the city of Johannesburg’s protected conserved areas and in wetlands. The invasive species are plants that are non-native to an ecosystem, and which may cause economic, environmental harm and/ or adversely affect human health. In particular, they impact adversely upon biodiversity, including decline or elimination of native plants - through competition, or transmission of pathogens (disease carriers) - and the disruption of local ecosystems and ecosystem functions.

The program will run till May 2017 and the objectives are to reduce the spread of alien plants through eradicating, controlling and managing the growth. Johannesburg City Parks and Zoo aim to educate and increase awareness amongst communities about the scourge with hopes that residents would remove alien invasive species from their gardens. Removal of invasive species will contribute to protecting Johannesburg’s biodiversity and water resources by eradicating alien plants.

Top ten category 1 alien plant species

alien1Acacia mearnsii, dealbata and decurrens (Wattle)

alien2Arundo donax (Giant Spanish reed)

alien3Campuloclinium macrocephalum (Pompom weed)

alien4Eucalyptus (Gum trees)

Cotoneaster francheti (Cotoneasters)Cotoneaster francheti (Cotoneasters)

Populus x canescens and alba (Grey and white poplars)Populus x canescens and alba (Grey and white poplars)

Robinia pseudoacacia (Black locust)Robinia pseudoacacia (Black locust)

Solanum mauritianum (Bugweed)Solanum mauritianum (Bugweed)

alien9Lantana camara (Tickberry)

Acacia melanoxylon (Blackwood)Acacia melanoxylon (Blackwood)


Invasive alien plants are combated by detecting at an early stage and eradicating them before they become established.

Biological control is an attempt to introduce the plant’s natural enemies to its new habitat, with the assumption that these natural enemies will remove the plant’s competitive advantage until its strength is reduced to a level comparable to that of the natural vegetation.

Natural enemies that are used for biological control are called bio-control agents.

In the control of invasive plants, the bio-control agents used most frequently are insects, mites and pathogens (disease-causing organisms such as fungi). Bio-control agents target specific plant organs, such as the vegetative parts of the plant (its leaves, stems or roots) or the reproductive parts (flowers, fruits or seeds).

The bio-control agents are mostly introduced from the country of origin of the plant.

Mechanical and Chemical methods include:

  • Basal bark: Application of suitable herbicide in diesel can be carried out to the bottom 250mm of the stem. Applications should be by means of a low pressure, coarse droplet spray from a narrow angle solid cone nozzle.
  • Ring barking: Bark must be removed from the bottom of the stem to a height of 0.75-1.0 m. All bark must be removed to below ground level for good results. Where clean de-barking is not possible due to crevices in the stem or where exposed roots are present, a combination of bark removal and basal stem treatments should be carried out. Bush knives or hatchets should be used for debarking.
  • Frill: Using an axe or bush knife. Make angled cuts downward into the cambium layer through the bark in a ring. Ensure to affect the cuts around the entire stem and apply herbicide into the cuts.

Where trees can be felled and removed use chainsaws, brushcutters or cane knives.

  • stump1Cut stump treatment: Stems should be cut as low as practical as stipulated on the label. Herbicides are applied in diesel or water as recommended for the herbicide. Applications in diesel should be to the whole stump and exposed roots and in water to the cut area as recommended on the label.

  • stump2Stem injection: Punch downward slanting holes into the main stem using a sharpened metal spike. Space holes around entire circumference of lower stems. Inject the herbicide directly into the plant – ensuring to inject around the stem.

Manual Removal

Hand pull: Grip the young plant low down and pull out by hand (using gloves).

Not everyone is allowed to apply herbicide. Only those who have certification


  • Herbicide certification obtainable from DAFF
  • Training in plant identification (certificate)
  • PPC (Overalls, safety boots, goggles, boots, gloves, helmets, dust masks, shin guards)
  • PPE (Chainsaw, knapsac/ hand spray, panga, cutting scissors)

NB! Climatic conditions must be sunny/ cloudy and calm. Do not apply when it’s raining and/ or windy. All the cut material must be loaded onto a truck and removed from site immediately.

Check out the latest Invasive spesies


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