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Triffid weed in KwaZulu-Natal

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Triffid weed or chromolaena (Chromolaena odorata) is an invasive weed of agriculture, forestry and conservation in many parts of the world. In KwaZulu-Natal, it rapidly degrades indigenous forests and savannas and is a weed problem in commercial plantations.

Research has shown that chromolaena is easily killed by herbicides applied to the foliage, stumps or to the soil at the base of the plant or by mechanical control.

Notwithstanding these efforts, the spread of the weed has not been curbed. Successful biological control remains the only viable solution for reducing the current and potential impact of chromolaena.

Where is this plant from?

Efforts have been made in finding out where the South African biotype originated from. The first place to look at was the herbarium specimens in the United States of America. It was found that morphologically, the South African biotype was more similar to the Jamaican and Cuban specimens, also from Guyana.

Researchers have ascertained that the South African biotype came from Jamaica and Cuba.

Biological control

Recent studies have clarified the morphological and genetic differences between the biotype of chromolaena invasive in Southern Africa and more widespread chromolaena biotype invasive in Asia and West Africa.

Incompatibility of biological control agents with the southern African chromolaena biotype has been suggested as a possible factor responsible for the limited success of the biological control of this weed in South Africa.

The first biological control agent to establish on chromolaena in South Africa, Parauchaetes insulata, a moth that was collected in Florida, USA, on chromolaena plants dissimilar to the southern African biotype.

This moth was first released in 2001 in South Africa. It was only present in southern KwaZulu-Natal for many years, but has recently been found in Zululand and Swaziland

Although this insect did establish at one site, out if 30 sites at which over one million individuals were released, its population level in the field generally remain low.

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CAPTIONS:

1. Triffid weed (Chromolaena odorata) flowers are white or pale blue in terminal, surrounded by speckled bracts.

2. It completely smothers and suppresses indigenous vegetation and known to replace up to 100% of indigenous vegetation in some regions.

3. Pareuchaetes insulata adults are nocturnal, and may be found around lights at night.

4. During the day, the younger larvae of pareuchaetes insulata often sit under the leaf near a hole that they have fed on the previous night.

5. Pareuchaetes insulata, a moth released for biological control of triffid weed feeding holes are quite characteristic but there are other invertebrates that make holes in leaves.