Clear those invasive plants

nd 4 Mexican sunflower Tithonia diversifolia Mexican sunflower (Tithonia diversifolia) is a category one invader which is now invading natural land and roadsides.

National WeedBuster Week runs until Saturday and gardeners are asked to identify and remove alien plants from their gardens. The awareness week represents the annual culmination of an ongoing campaign to manage and contain invasive alien plants. It is an initiative led by the Department of Environmental Affairs through the National Resource Management Programmes (NRMP) and supported by various partners and stakeholders.

Here are some facts:

What are invasive alien plants?

Invasive alien plants (IAPs) have been introduced to South Africa, either intentionally or unintentionally. They have established natural populations and are spreading out of control to the detriment of indigenous vegetation and water resources.

Why are they a problem?

They are highly adaptable, vigorous plants that easily invade a wide range of ecological niches. They have invaded more than 10 million hectares of land to date and experts maintain that more than 7 percent of all water run-off is lost to IAPs which use 3.3 billion cubic metres of water – much more than their indigenous counterparts.

nd1 Lantana Lantana camara Pic L Otto Lantana (Lantana camara) is a category one invader which thrives in the humid coastal areas of KwaZulu-Natal. Pictures: L Otto, W Schmidt

They also threaten our rich biodiversity by replacing indigenous and endemic vegetation. This in turn will threaten species that are dependent upon indigenous plants for food and shelter. They are known to exacerbate the intensity of fires, flooding, erosion and siltation.

Durban’s garden invaders

Our subtropical climate ensures prolific plant growth, but the indigenous vegetation is being strangled by a proliferation of invasive alien plants. Some of the most problematic invasive plants from Durban gardens include lantana (Lantana camara), balloon vine (Cardiospermum grandiflorum), bugweed (Solanum mauritianum), castor-oil plant (Ricinus communis), triffid weed (Chromolaena odorata), Indian laurel (Litsea glutinosa), inkberry (Cestrum laevigatum), Mexican sunflower (Tithonia diversifolia), seringa (Melia azedarach) and yellow bells (Tecoma stans).

The law and invasive species

There are 198 invasive plants listed in three categories under the Conservation of Agricultural Resources Act. Plants listed in category one may no longer be grown anywhere in South Africa and if they grow in your garden, they should be removed and destroyed immediately. Trade in these plants is prohibited.

How to remove invasive plants from your garden

nd 3 Yellow bells Tecoma stans Pic W Schmidt Yellow bells (Tecoma stans) is a popular ornamental tree, but may not be grown in the garden as it is listed as a category one invader.

When seedlings appear, pull them out.

Shrubs and small trees can be cut off and the crown and roots then removed from the soil.

Large trees need to be ring-barked, which involves removing a ring of bark from the stem of the tree near ground level.

There are also a number of effective herbicides on the market. Avoid dumping cuttings and removed plants in open landfill sites, as they may take root and spread into neighbouring land.

Celebrating biological control

South Africa is a world leader in the field of biological control and it is the official theme of this year’s WeedBuster Week. Biocontrol involves the use of a plant’s natural enemy and includes insects, mites and fungi. The first biocontrol agent released in South Africa was against the drooping prickly pear (Opuntia monocantha), which was a problem along the South African coast.

For more on the identification and removal of invasive alien plants, visit the Invasive Species South Africa website www.invasives.org.za – Lifestyle Reporter


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