Origin and Distribution

Pompom weed has a wide natural distribution that extends from Argentina in South America to Costa Rica and Honduras in Central America and Mexico. How or when the plant was introduced into South Africa remains unknown. The earliest record in the Pretoria National Herbarium is of a specimen collected in Johannesburg in 1962. Currently it is most prominent in Gauteng, but also occurs in Mpumalanga, Limpopo, NW Province, KwaZulu-Natal, E Cape and Free State.

The earliest record of its establishment in the wild is from Fountains Valley, Pretoria in the early 1960s and Westville near Durban in 1972. In the 1980’s its distribution expanded in the Pretoria area, and it was also recorded from Hilton in KwaZulu-Natal and Wolkberg in Limpopo Province. In the 1990’s it spread further to Port St Johns in Eastern Cape, Rooiberg in Limpopo and Nelspruit in Mpumalanga. From 2000 to 2003 it exploded in Gauteng and was recorded for the first time in the Free Sate at Kroonstad. During the same period there was wide spread in the Nelspruit, White River and Barberton areas. By 2006 it had spread to the Piet Retief area in southeastern Mpumalanga and Swaziland. (compiled by Lesley Henderson, Jeremy M Goodall & Hildegard Klein, ARC-Plant Protection Research Institute, revised September 2006)

About the Pompom Weed (ARC LNR, 2014)

It is rapidly becoming the most serious threat to the conservation of grasslands in South Africa. Infestations become conspicuous when the plants are in flower between December and March, transforming the veld from green to pink. The plant initially establishes itself in disturbed sites such as roadsides, but then invades natural grasslands, open savanna and wetlands. This weed displaces native species, reducing both the biological diversity and carrying capacity of wetlands and veld. During winter the plant is not visible above-ground.

The plant has evolved to be the perfect opportunist. One pompom can drop 300 seeds a season. These survive any fluctuations in temperature and rainfall. In winter, the plants wither away and all that remains are the roots, keeping them safe from the veld fires that kill off any indigenous competition. And in spring, people unwittingly aid the spread of the weed by picking the flowers.

Pompom weed is a perennial, erect herb up to 1.5 m high. The stems and leaves are covered with rough, bristly hairs. Leaves are scattered along the length of the stem but clustered at the base to form a rosette. The plant has a short woody rootstock that ends in thick tuber-like perennial roots. In spring, shoots arise from, and in autumn die back to, the rootstock. The showy pink flowerheads (inflorescences) are produced in dense clusters at the ends of the aerial stems and look like bright-pink powderpuffs.

Each flowerhead, measuring 15 mm long × 25 mm wide, consists of hundreds of tiny, star-shaped florets (individual “flowers”) surrounded by purple bracts (brightly coloured, leaf-like scales). A long, protruding style from each floret gives the flowerhead a fluffy appearance. Mature florets each produce a single-seeded dry fruit (achene) with a tuft of brown hairs (pappus) that promote wind dispersal.

Pompom weed is a listed invasive species (category 1b plant) in terms of the IAS Regulations (August 2014) of the National Environmental Management: Biodiviersity Act, (NEM:BA) (2004). It is illegal to harbour, plant, propagate or sell pompom weed. Landowners are therefore compelled to control pompom weed by whatever means are deemed appropriate.  Information courtesy of the Agricultural Research Council (ARC LNR, 2014)

Control Measures – Biological Control Methods:

Liothrips Tractabilis

The pompom thrips, Liothrips tractabilis, is native to Argentina. The insect was collected there on Campuloclinium macrocephalum (pompom weed) in 2005 and imported to South Africa where it was cultured and tested in quarantine to demonstrate that it is host specific (does not feed or lay eggs on any other plants) and is damaging to pompom. This was shown to be the case, and permission for its release was granted by South African authorities on 18 June 2013. The first insects were released at various sites in Gauteng, Mpumalanga, Limpopo and North West Provinces in the summer of 2013/2014. These releases are on-going, . The distribution map will be completed as soon as this information is available.

Life Cycle

Adult pompom thrips lay eggs either singly or in clumps on the stems and leaves of pompom (ii). They hatch after about 10 days at 25°C. The pompom thrips has three nymphal instars and two pre-adult stages. The nymphal period lasts approximately 11 days, while the pre-adult stage lasts about seven days. Egg to adult duration is about 28 days

Impact on Pompom Weed

Biological control represents the only long-term, sustainable solution for controlling pompom weed. It is hoped that the pompom thrips will combine synergistically with the already present pompom rust to manage this weed. With its high reproductive rate and ability to disperse, the thrips should have a marked impact on its target. (ARC LNR, Besaans,L. 2014)

Puccinia Eupatorii

The pompom rust fungus, Puccinia eupatorii Dietel, was collected in 2003 in northern Argentina as a biological control agent against pompom weed (Campuloclinium macrocephalum (Less.) DC.). Owing to its high specificity and virulence on pompom weed, the rust fungus was considered to be suitable for release in South Africa. However, in 2006, a rust fungus was discovered on pompom weed in the Pretoria area, and was confirmed to be the same species. Since then, pompom rust has spread through wind dispersal to most areas invaded by the weed.

Life Cycle

Wind-dispersed urediniospores germinate and infect the leaves and stems from the start of the summer rainfall months and continue until March. Germination occurs at tempera-tures between 15 and 20°C, with 6 to 12 hours of high humidity. Infected leaves and stems turn yellow (iii), and the rust fungus becomes more visible as the brown pustules emerge on both the upper and lower surfaces of the leaves. Heavily infected pompom plants lose their leaves and dieback occurs. The pompom rust fungus overwinters as teliospores, reinfecting the pompom plants as they emerge at the start of summer.

Impact on Pompom Weed

The leaves (both sides) and stems of infected plants are covered with noticeable brown pustules. Heavily infected plants will turn yellow (iv). Unfortunately, despite the presence of this fungus, pompom weed populations have remained constant – largely due to the plant’s perennial rootstock, which produces annual stems in spring (September/October), and die back in autumn (May). Nevertheless, augmentative releases of the pompom rust fungus early in spring could potentially cause greater dieback throughout the growing season, resulting in less rootstock growth and seed production. (ARC LNR, Besaans,L. 2014)

Control Measures – Physical Methods:

uprooting or hoeing are ineffective and make the problem worse through disturbance. It is not advisable to plough lands with pompom weed as this will damage the rootstock, stimulating further vegetative growth and denser stands. Spread of the plant can be limited by preventing seed production. Aerial stems can be cut right back before the flowers produce seed.

However, be warned that the plants will be stimulated to produce more stems and in order for this method to work the plants will have to be cut back several times until the end of the growing season. Repeated cutting back of aerial growth should deplete nutrients stored in the roots, weaken the plant and limit seed production. This method however is only practical on a small scale. Where there is little pompom weed it is advisable to remove all cut stems from the roots. (ARC LNR, Besaans,L. 2014)