The pink invader that is taking over our grasslands

Pompom weed is an Argentinian plant in the daisy family, with its striking pink powder-puff-like flowers. It is a serious threat to the conservation of South African grasslands. The first record of its presence was from Johannesburg in 1962 when it began invading disturbed areas along roadsides and unused fields. The weed is now prominent throughout Gauteng Province.

Under the NEMBA Alien and Invasive Species Regulations, pompom weed is listed as a Category 1b invader in Gauteng, North West, Limpopo and Mpumalanga and Category 1a in the rest of South Africa, meaning that every effort must be made to remove and destroy it.

The distribution of pompom has almost doubled in the past five years. It threatens grasslands, open savanna and wetlands by decreasing the carrying capacity of the land. The plant is unpalatable to wildlife and agricultural livestock.

It also threatens indigenous herbs and grasses. It is almost impossible to control mechanically due to its robust root system and copious seed production. Herbicide application is expensive and labour intensive and therefore restricted to roadsides and smaller, manageable areas, so biocontrol is deemed to best long-term solution to control pompom weed.

Biocontrol agent

On 23 October 2013, the thrips (Liothrips tractabilis) was released in Pretoria at Rietvlei Nature Reserve. Additional releases were made a month later at Swartkop Airforce Base and Rietondale (ARC-PPRI research farm) and Roodeplaat Nature Reserve. At the beginning of December 2013, releases were made at a further six sites around Pretoria.

Recruited from Argentina, where pompom weed is indigenous, the pompom thrips causes significant damage to the stems and leaf tissue at the growing tips. This causes deformities in plant growth, reducing the height, biomass and flower production of this unwanted weed.

A second promising biocontrol agent for pompom weed is the flower-feeding moth (Cochylis campuloclinium) which is still undergoing testing by scientists in quarantine facilities around the country.

How to control pompom weed on your property
Herbicides registered for use on pompom weed are Plenum, Access and Climax. The two physical methods include uprooting and burning of the plant. Herbicides must always be used in accordance with the manufacturer’s guidelines as well as national and provincial regulations.

Anyone wanting to include biological control in their management strategy against pompom weed can have their names, contact details and locality added to an existing database by contacting: Almie van den Berg (This email address is being protected from spambots. You need JavaScript enabled to view it.) or Liamé van der Westhuizen (This email address is being protected from spambots. You need JavaScript enabled to view it.).