Alien plants

What are invasive alien plants?

Invasive alien plants have been brought to South Africa from other countries for their beauty, economic value or an ecological purpose. As they are without their natural enemies in South Africa, they reproduce and spread prolifically. The plants or seeds enter the country in different ways, for example on people’s shoes, tents, and by mail order on ships and planes. Even animals that cross the borders can bring seeds in. The invader plants and seeds spread rapidly and take up the growing space of our indigenous plants. Invasive alien plants threaten the indigenous vegetation as they use up valuable and limited water resources. Most of them drink more water than indigenous plants and are depleting the underground water resources. Many invasive plants are also responsible for causing exceptionally hot fires and affect the makeup of the soil. Negative impact of weeds and invader plants

Weeds and invader plants are associated with the following negative impacts.

They:

• Compete with the agricultural environment;
• Impact negatively on natural vegetation;
• Displace indigenous plants and animals;
• Increase the severity of fire;
• Consume more water than the indigenous plants and therefore lead to the loss of water in catchments; and
• Cause obstruction and erosion, and increase flood damage.

What can I do?

• Learn how to identify and control (remove) invasive alien plants.
• Join or form a hacking team to remove invaders from your area.
• Remove invasive plants while they are still small.
• Plant indigenous (local) plants in your garden.
• Buy only indigenous plants from your nursery.
• Replace invasive alien plants with indigenous plants.
• Tell people about the dangers of invasive alien plants.

Control methods

When controlling weeds and invader plants in areas where they are not allowed in terms of Regulation 15 of the Conservation of Agricultural Resources Act (CARA), control methods should be used that are appropriate for the species concerned, as well as for the ecosystem in which they occur.

One or a combination of the following control methods may be used: uprooting, felling, cutting, burning, treatment with registered herbicides, biological control or any other recognised and appropriate method. Repetitive follow-ups are necessary to achieve control.

Biological control is the use of host-specific natural enemies such as insects or disease-causing micro-organisms to destroy alien plants. Before introducing agents, scientists first test these natural enemies in the plant’s country of origin extensively under quarantine conditions to ensure that they will not damage crops or other plants in South Africa.

Invaders in Tshwane

Category 1: Declared weeds

These plants must be controlled (removed) on land or water surfaces by all land users. These plants may no longer be planted or propagated and all trade in their seeds, cuttings or any other propagation material is prohibited. Category 1 plants:

Lantana, pompom weed, bug weed (Solanum Mauritianum), azolla, queen of the night, pampas grass, cat’s claw creeper, red sesbania, yellow oleander, yellow bells and water hyacinth

Category 2: Declared invaders with commercial value

These plants pose a threat to the environment but they are a source of fruit, fuel, medicinal extracts, animal fodder, building material or shelter, or they can be used to stabilise soil. These species are only allowed to occur in demarcated areas. If the plants are used for commercial purposes, land users have to obtain a water-use licence, as the plants consume large volumes of water. Where the plants occur outside demarcated areas they have to be removed. Category 2 plants:

Black wattle, patula pine, sisal, red eye, grey poplar, watercress, Port Jackson willow, guava, cluster pine, honey locust, weeping willow (not to be confused with the indigenous willow)

Category 3: Declared invaders with ornamental value

These plants can become invasive but are considered to have ornamental value. In terms of Regulation 15 of CARA, the plants are not allowed to occur anywhere except in biologically controlled reserves, unless they were already in existence when the regulation came into effect (30 March 2001). This means that existing plants do not have to be removed by the land user. However, they must be kept under control and no new planting may be initiated and the plants may no longer be sold. Category 3 plants:

Jacaranda, syringa, Australian silky oak, St Joseph’s lily, sword fern, Tipu tree and New Zealand Christmas tree

More information can be obtained from:

• http://www.agis.agric.za/agisweb/wip
• http://www.nda.agric.za/docs/landcare/landcare.htm
• http://www.weedbuster@dwaf.gov.za

Weedbuster hotline: 0800 005 376 0800 005 376