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December 2013

As the year draws to a close, we deviate from our series describing the identification and control of Invasive Alien Plants (IAP’s). Since 2013 marks the 100th anniversary of Biological Control of IAP’s in South Africa, it is appropriate that we take a closer look at this programme in this, the last issue of 2013.

The tiny gall fly had a big impact on invasive black wattle


A beetle of the genus Zygogramma targets famine weed.
Photo courtesy of Agricultural Research Council

South Africa is regarded as one of the world leaders in the field of biological weed control, which is the use of natural enemies such as insects, mites and pathogens to reduce the vigour or reproductive potential of IAP’s. Plants become invasive when introduced to a new region without their natural enemies. They therefore gain a competitive advantage over our indigenous vegetation because all indigenous plants have their own natural enemies that feed on them or cause them to develop diseases.

In the past 100 years bio-control programmes have been initiated against more than 50 plant species and have provided complete to substantial control of 27 species. These species include several notoriously invasive cacti such as Sweet Prickly Pear and Jointed Cactus as well as the mat-forming, floating aquatics such as Water Hyacinth, Salvinia and Red Water Fern.
The potential risk posed by a candidate bio-control agent is determined by bio-control researchers through extensive host range studies carried out in a quarantine facility. These trials determine the range of plants that a potential bio-control agent is able to use as a host plant through its life cycle. The candidate agent must only target one host species or it may have a wider host range, provided that none of these occur in SA or surrounding countries either as indigenous or introduced crop plants.

Mass rearing of bio-control agents is carried out at the SA Sugarcane Research Institute (SASRI) at Mount Edgecombe in KZN. From here, they are despatched by courier all over SA for release against problematic invasive weeds. Monitoring of the establishment and spread of agents on the weeds is important and the public can play a big part in this respect.

Bio-control has to be integrated with other control methods since it only gives complete control of a few species. The integration of biological, mechanical and chemical control methods is therefore essential for successful control.

Sources: SA Plant Invader Atlas (SAPIA) News No. 21 & 29

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January 2014

After Indonesia and Brazil, South Africa is the third-most biologically diverse country in the world. Occupying only 1% of the world’s terrestrial land area it is home to...

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December 2013

Since 2013 marks the 100th anniversary of Biological Control of IAP’s in South Africa, it is appropriate that we take a closer look at this programme in this, the last issue of 2013.



November 2013

This month, we describe the first two alien invaders that are currently quite evident in our area as they are early spring bloomers

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October 2013

One of the prime causes of habitat degradation - namely the introduction of alien plant species.

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September 2013

Biodiversity is the all-encompassing term to describe the variety of all life on Earth.

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February 2014

This month, we revert to our series on Alien Invader Plants (AIP’s) and how to identify and eradicate them.

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March 2014

As promised last month, our next “candidate” is the notorious weed Lantana camara.

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