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Scientists deploy ‘insect army’ in war against water hyacinth weed at Harties

Boats stuck in invasive green water hyacinth weed at Hartbeespoort Dam in the North West.
Boats stuck in invasive green water hyacinth weed at Hartbeespoort Dam in the North West.

The Hartbeespoort Dam in the North West used to be brimming with people enjoying scenic landscapes and recreational water sports. These days visitors are greeted by the sight of boats stuck in a sea of invasive green water hyacinth weed.

The spike at Harties, as Hartbeespoort is known, can be attributed to pollution, with sewage, industrial chemicals, heavy metals and litter flowing in rivers from Johannesburg and Pretoria.

We are only treating the symptom of a much larger problem.
Kelby English, scientist at Rhodes University.

“We are faced with highly polluted waters,” said Prof Julie Coetzee, who has studied water hyacinths for more than 20 years and manages the aquatic weeds programme at the Centre for Biological Control at Rhodes University.

Nutrients in the pollutants act as perfect fertilisers for the weed, a big concern for nearby communities due to its devastating impact on livelihoods.

Dion Mostert, 53, is on the verge of laying off 25 workers at his recreational boat company after his business came to a standstill because of the carpet of water hyacinths.

“The boats aren't going anywhere. It's affecting tourism in our town, tourist jobs,” Mostert said, pointing towards his luxury cruise boat Alba marooned in the weeds.

He has considered using herbicides but admitted it would only be a quick fix against the weed.

Scientists and community members have, however, found a unique way to deal with the invasion by introducing a water hyacinth eating bug called Megamelus scutellaris.

The tiny phloem-feeding insects are the natural enemy of the plants. Both are originally from the Amazon basin in South America and are released by the thousands at a time.

The insects destroy the weed by attacking tissue that transports nutrients produced in the leaves during photosynthesis to the rest of the plant.

The insect army has previously reduced the expanse of water hyacinths to 5% on the dam, Coetzee said. At times the weed has covered at least 50% of it.

Environmentalist Patrick Ganda, 41, mass rears the bugs at Grootvaly Blesbokspruit wetland conservancy southeast of Harties, once home to more than 100 species of birds, which attracted a lot of tourists.

Unable to find food such as fish and small plants with much of the wetland's water covered in plants, there are only two to three species of birds left, he said.

Scientists warned that while the insects have been fairly successful in controlling the situation, more needs to be done to treat its cause, which authorities could tackle by tightening regulations on waste water management.

“We are only treating the symptom of a much larger problem,” said Kelby English, a scientist at Rhodes University.


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