The pompom weed — a plant in the daisy family — is rapidly becoming one of the most serious threats to the conservation of South African grasslands, the Working for Water programme said on Thursday.
”The weed produces enormous amounts of wind-dispersed seeds every summer, and has underground tubers that enable it to survive fires and the dry season,” said spokesperson Theo Rossouw.
In addition, the weed’s beautiful flowers are leading members of the public to collect and inadvertently spread it to more places, Rossouw said.
”We know that it originates from South and Central America but don’t know when or how it got into South Africa.”
He said the first record of the presence of the weed was from Johannesburg in 1962.
The weed is prominent throughout the Gauteng province, and occurs in Mpumalanga, Limpopo, North West, KwaZulu-Natal, Eastern Cape, the Western Cape and Free State.
Rossouw said several strategies have been implemented to control the pompom weed throughout the country.
The first involves creating awareness of the weed, because it is very conspicuous during its flowering period (December to March), he said. Members of the public can identify, report and even control outlying pompom populations.
The second strategy has already been implemented in KwaZulu-Natal — all known infestations of the weed have been treated with one of two registered herbicides for pompom in South Africa. The plants were spot-sprayed to minimise the effects on non-target plants. A follow-up programme will be conducted in early 2008.
Chemical programmes in other affected provinces have mainly focused on spraying roadside infestations of pompom weed, in order to minimise the dispersal of seeds by vehicles, he said.
”Biological control is the final strategy for sustainable control in the fight against pompom. This involves the introduction and release of effective yet safe insects or disease-causing organisms to reduce the invasiveness of the weed.”
He said researchers had undertaken three exploratory trips to Argentina and one to Brazil to search for natural enemies. Two leaf rust fungi and nine insect species were found on the plant in its native range — of these, one rust fungus and three insect species are currently being reared and tested in quarantine in South Africa, Rossouw said.
”The results from laboratory host-specificity trials so far indicate a narrow host range and it is envisaged that applications for permission to release the rust may be submitted towards the end of 2008 and the insects at the end of 2009.” — Sapa