The pretty pink flowers you see in concentration in the grassland along the left side of the Rocklands 13th fairway and dotted in several other areas on the Greater Woodmead Estate any time from November through to March is the Pompom weed.
This is an invasive weed of our grasslands, savanna and wetlands and listed as a Category 1 invasive alien species. Plants from this category are prohibited on any land or water surface in South Africa and must be controlled or eradicated where possible.
Infestations become conspicuous when the plants are in flower between November and March transforming the veld from green to pink. The plant initially establishes itself in disturbed areas such as roadsides then invades natural grasslands, open savanna and our wetlands where the weed displaces native species reducing both the biological diversity and carrying capacity of vleis and veld.
WHERE HAS THE POMPOM COME FROM?
Pompom weed commonly known as this in SA, is a South American invasive plant that was first recorded in South Africa in the early 1960‟s. Then in the 1980‟s, pompom started slowly extending its range and in the 1990‟s and 2000‟s it entered a dramatic expansion phase.
How the pompom was introduced to South Africa remains unclear but it is thought to have come in from Argentina in bales of imported hay. The plant is increasingly disrupting conservation of grasslands in South Africa and without intervention it could invade the entire grassland biome. The weed it is feared could potentially spread across a greater region than Gauteng, Limpopo, Mpumalanga and North-west Province where it is presently recorded.
The absence of natural enemies better explains the plant‟s ability to invade. While the weed has been shown to cause a significant decline in plant diversity, its impact on insect diversity has not yet been noted. To date mechanical and chemical methods have been relied on to control pompom. Many of these methods have proved ineffective while mechanical approaches have been found to exacerbate infestations through disturbance.
Cutting the flower heads a route initially prescribed appears not to be sufficient, during the pompom growing season. The stems where the flowers have been cut grow up to five new stems, each bearing a flower. Effectively the flowers are five times more when the stems are cut during the growing season.
While herbicides are not ideal for environmentally sensitive areas several have been registered for use on pompom, especially for roadside applications.
NEW BIO CONTROL WEAPON!
“Tiny insect wages war on weed…..”
Due to the extent of the invasion, the financial and environmental costs of treating all pompom infestations with herbicides would be prohibitive. As a result, a biological control program was initiated against the weed in 2003.
Professor Walter BARKER from the Wits dendrological society after a visit to the Greater Woodmead Estate in January 2013 warned the then TEC (the CCJ tree and environment committee) of this scourge invading our grasslands and advised us that it required urgent attention. Several ineffective approaches were followed. The pompom infestation remained as bad and out of control.
Then purely by chance in February of this year I came across an article in the Star 48 HOURS section about this tiny insect Liothrips tractabalis being used as the new bio control weapon. It had just been released against the spread of the “beautiful but invasive pink – flowering pompom weed, a Category 1 invasive alien species”
This little insect was recruited from Argentina, where pompom weed is indigenous. The tinyliothrips causes significant damage to the stems and to the leaf tissue at the growing tips, causing deformities in plant growth, reducing the height, biomass and flower production of this unwanted weed. Can you believe that scientists have been
working with liothrips since 2005, when they collected parent stock from Argentina? The liothrips was quarantined as soon as it arrived in South Africa and underwent rigorous testing in the quarantine labs to ensure it would only feed on the host plant and not threaten indigenous plants or agricultural crops. Liothrips was cleared for release in June last year and the insect was released into selected sites around Gauteng, Mpumalanga, Limpopo and North-west Provinces.
This led me to get in touch with the Agricultural Research Council (ARC ) – Plant Protection Research Institute and am happy to report that we are on the list and included in the program to receive the „little insect‟ sometime in November/ December.
For good results from this bio control method the plant has to have enough re growth (young shoots and leaves) as there must be enough food to sustain the insect‟s development. Pompom has a perennial rootstock that produces annual stems in spring (Sept – October) that can grow to 1.3 meters in height. The plant stems age in autumn (May) and the plant survives as rootstock during winter. Winter is the dry season and the pompom is not adversely affected by grass fires, frost and next to no rainfall at this time of the year. The showy flower heads are produced in dense clusters at the ends of aerial stems .Each of these flower heads consists of hundreds of tiny star-shaped florets, surrounded by purple bracts.
This bio control method is funded by the Government and it is ARC that makes the releases. They will come to CCJ and show us exactly what needs to be done. They cable tie a piece of damaged thrips infected plant that shows the deformities and the damage to the plant, to a “healthy“ pompom cluster of plants. This little thrips insect is then able to go about its task of “causing problems for the healthy plant”.
Significant reductions in numbers of the plant can only be expected in 5 years. It seems as though pompom cannot be completely eradicated but in and over 5 years this scourge invading our grasslands will hopefully become manageable. The insect needs time to multiply for inroads into this plant explosion to be noticed.
This is not a „quick fix„ solution but it seems the eco balance will ultimately be restored. The decision taken to follow the bio control route must be the correct way to go as the herbicide route is cost prohibitive and invariably only a short term solution as the pompom will just keep returning!
So when next on the open road and you drive by a field of pink fluffy flower heads stretching as far as the eye can see don‟t stop and pick a bunch to take home. The flowers might be beautiful, but the sea of pink flowers could be the pompom weed which is seriously out competing local grasses and turning valuable agricultural land into pink – flowering wastelands. Our perception of this weed desperately needs to change.