10 Aug 2017

Human activities such as fishing and boat cruises are responsible for the increase and spread of Kariba weed or salvinia molesta weed along the Tlhamalakane River, says Dr Naidu Kurugundla.

Speaking at a stakeholders workshop in Maun recently, Dr Kurugundla described  the weed as a floating aquatic plant which has the potential to block the water system and affect the ecosystem if not controlled or eliminated.

Dr Kurugundla, who is a specialist with the Department of Waters Affairs in Maun, said human activities negatively impacted on their efforts to eliminate the weed.

Dr Kurugundla added that the weed was now threatening the Okavango swamps.

He noted that the weed had no seeds, but that it was easily moved from one place to the other through various human activities.

He said the recent infestations in the Tlhamalakane River were first seen at the Matlapana Bridge and Borolong Treatment Plant.

Dr Kurugundla said the Matlapana Bridge infestation and those in Nxaraga were likely caused by fishing nets relocations.

He, however, said weevils were the answer to eliminate the weeds for the DWA, adding that they solely feed on the weed, which was first discovered at Lake Kariba in Africa.

Dr Kurugundla said weevils were worms that the government of Botswana and Namibia had used eliminate the weed in the Chobe/Linyanti area around 1983.

He said the weevils were discovered in South East Brazil in 1980, and were initially used in Australia before being adapted by other countries which were facing the same challenges of the weed.

He noted that the Kariba weed was concentrated in the Moremi Game Reserve area before 2000, following the first infestation in the Linyanti/Chobe area and Okavango before 1980.

He said heavy rains, floods, people and hippopotamus’s were also responsible  for the spread of the weed.

Dr Kurugundla said the other method of eliminating the weed was by cutting and burning the weed, but said it was now difficult because the Tlhamalakane River had become a perennial river instead of seasonal.

“It is in the midst of other vegetation and, therefore, a challenge to remove physically when the river is flowing,” he said.

He said the DWA carried regular surveys of wetlands to monitor the devil weed.

Stakeholders who attended the workshop asked how the department ensured the weed does not infest other important sites and areas such as Lake Ngami.

Some advised that the department should embark on a public campaign and awareness on the weed. ENDS