Allergenic ragweed is NOT new to South Africa

On 20 January 2020, a media release entitled, “Pollen Alert: Highly allergenic ragweed invades SA” was issued by Meropa Communications on behalf of the University of Cape Town Lung Institute.

The media release reported that ragweed had been detected in a pollen trap in Westville, Durban and represented a new invasion in South Africa.

On 5 February 2020, weed scientists, invasion biologists and biocontrol specialists released information which indicated that ragweed is not new to South Africa.

Moreover, suggestions that ragweed is a brand new invader to South Africa are not only factually incorrect, but also spread unnecessary panic.

Ragweed has been in South Africa for over a century

Botanical records and herbarium specimens show that ragweed (Ambrosia artemisiifolia) is widespread and was recorded in …

1896 in Wynberg, Western Cape
1910 in Camperdown, KwaZulu-Natal (Hillard, 1977)
1946 in Pretoria (Hillard, 1977)
1966 in Gouda, Free State (Hillard, 1977)
2003 in Limpopo, NW, Gauteng, Mpumalanga, KZN and N Cape (Germishuizen and Meyer 2003)
South Africa weed scientist, Lesley Henderson says,

“I can confirm that three species of Ambrosia are known in South Africa. Ragweed (A. artemisiifolia) is especially widespread and the earliest herbarium specimen dates back to 1896.
Herbarium records from the South African National Biodiversity Institute’s (SANBI) BRAHMS online reflect it’s widespread distribution. The database can be accessed at the following web address:
SANBI’s BRAHMS online database shows that Ambrosia artemisiifolia has been recorded for some time in localities where pollen spore traps are located e.g. around Durban, but this is only the first time that they have detected it.
It is probable that the good rains in parts of the country have favoured the growth of ragweed and this is why the species has been detected in spore traps.”

Distribution Map

Three Ambrosia species are known to have naturalized in South Africa and to the untrained eye they look fairly similar: A. artemisiifolia, A. psilostachya and A. tenuifolia.

The map above shows confirmed populations of all three species. Most data was sourced from the Southern African Plant Invaders Atlas (SAPIA).

Ambrosia tenuifolia is known to occur only in the Eastern Cape and Ambrosia psilostachya has very finely dissected leaves resembling those of fennel.

Of these three Ambrosia species, it is most likely that famine weed could be confused with A. artemisiifolia due to their similar morphology and growth forms.

Ragweed ID Kit

Ragweed (Ambrosia artemisiifolia) also looks remarkably similar to famine weed (Parthenium hysterophorus).

In 2015, Reshnee Lalla (SANBI Invasive Species Unit) developed an illustrated kit for field workers that highlighted how to differentiate the three ragweed species found in South Africa (Ambrosia spp.) from famine weed (Parthenium hysterophorus).

This ID Kit is intended for use as a broad guideline only, as exceptions do occur due to the many factors that affect the growth and vigour of individual plants and populations.

Download the Ragweed vs Famine Weed ID Kit. Example of a page from the 15-page ID kit (above).

Lorraine Strathie, a biocontrol scientist working on famine weed says:

“I have not seen ragweed (A. artemisiifolia) in particularly dense stands in my fieldwork – which is conducted mostly in parts of KZN and Mpumalanga. I have only ever seen small, isolated patches.
It is good to be aware of this plant, but it is not immediately problematic, as the article inferred, creating panic”.
Are there any biocontrol agents for ragweed?

Lorraine Strathie says:

There are a few biological control agents for ragweed (A. artemisiifolia) available in the world.
Epiblema strenuana – which is currently being screened for suitability for famine weed (Parthenium hysterophorus) – is also a biocontrol agent for ragweed (A. artemisiifolia).
Epiblema strenuana is currently being screened with regards to South African indigenous plants. There may be complications that need to be resolved with regards to its host range further afield as this stem-galling moth is not monophagous – ie not restricted to a single host species.

Ragweed …

Has been present in South Africa for more than a century;
Is relatively widespread across South Africa;
Is currently NOT regarded as a problematic ‘invasive weed’ by scientists working in the invasion biology sector in South Africa.
Against this backdrop, the scientists conclude that there is no need for panic regarding ragweed’s ‘arrival due to climate change’… as indicated in the original press release… and regretfully distributed and amplified in features published by Health24, Timeslive and numerous other media.


Original Press Release

POLLEN ALERT: Highly allergenic Ragweed invades SA

On 20 January 2020, a media release was issued by Meropa Communications on behalf of the University of Cape Town Lung Institute. This is the information issued in the media release:

Discovery of ragweed pollen in Westville, Durban

A highly allergenic weed known as ragweed – and native to North America – was detected in a pollen trap in Westville, Durban, for the very first time.
The discovery was made by Dr Dilys Berman, an aerobiologist at UCT and Prof Jonny Peter, who heads up the UCT Lung Institute’s Allergy Unit.
Palynologist, Dr Frank Neumann, based at Wits University whose research focuses on the impact that climate change has on vegetation, also confirmed that the pollen grains indeed belong to the invasive Ambrosia species.
Linking ragweed arrival in South Africa to climate change

Prof Peter says while the threat of allergic plants, such as ragweed migrating southward, because of climate change, has always been a concern, little did they know it was going to show up so soon.
“Ragweed is incredibly invasive, and its potent pollen has been problematic in the US for many decades. In recent years, allergy sufferers in Europe and South America have also come under threat as ragweed started to invade these areas.
“For now, KwaZulu-Natal residents are most at risk as ragweed pollen has recently been detected at the Durban monitoring site over the last few days. The counts are relatively low at this stage, but we are monitoring them daily to detect any sudden spikes. A small population of ragweed has also been found on the banks of the Vaal River near Heidelberg – about 50km away from Johannesburg, while the Eastern and Western Cape still remain ragweed-free.
“Based on historical data, ragweed thrives in hot, dry environments and produces more pollen when CO2 levels are high,” he says.
Prof Peter points out that because of the world’s changing climate, ragweed is projected to decline in some areas as it may over time no longer be climatically suitable to grow there.
“Either way you look at it, ragweed is on the move. Once it sprouts, it can multiply and grow up to 2 metres in height in a matter of weeks.
“Weed control boards should add it to their invasive weeds list as soon as possible if they haven’t done so already and removal thereof should be a priority before it becomes impossible to control.
Some studies also suggest that ragweed poses a threat to crop health. It drains the soil and oppresses plant growth, so is definitely a weed that should be kept an eye on and monitored carefully,” he says.
Ragweed pollen is a health risk for allergy sufferers

UCT aerobiologist, Dilys Berman warns that ragweed poses a serious implication for human health.
“It’s been one of the most loathed weeds in the US, causing misery for 23 million Americans and it’s estimated that ragweed allergy rates in Europe will increase from 33 to 77 million in the next two decades. While we haven’t reported sensitisation in SA yet, it is a cause for concern.
“Increasing amounts of fine-powder ragweed in SA could exacerbate hay fever symptoms and asthma for the estimated 17 million South Africans who suffer from allergies.
“Given that its highly allergenic, people who normally don’t suffer from pollen allergies, may develop a sensitivity to it in the future as the weed proliferates.”
Common hay fever symptoms include red, itchy and watery eyes, a runny, itchy or congested nose, post-nasal drip etc, which could irritate and restrict the airways making it difficult to breathe
Pollen monitoring in SA is funded by Clicks, Twinsaver, Thermo Fischer, A.Vogel Echinaforce, Zeiss and Durand.
To expand pollen monitoring efforts, financial contributions can be made by logging on to Pollen counts for SA can also be viewed on the same site.
Issued by Meropa Communications on behalf of the UCT Lung Institute. For further information, please contact Brigitte Taim from Meropa on 021 683 6464; 082 410 8960 or email: