Despite its being gazetted as a noxious weed in April 2010, and its threat to biodiversity, agriculture and human health, parthenium (Parthenium hysterophorus) continues to spread across as no government institution or department is yet to act to contain it.

Worryingly, the plant with the pretty white flowers is everywhere (including Nairobi) and spreading faster than the Prosopis jullifora (mathenge) and the water hyacinth even as the relevant agencies argue over who is to take it on.

According to Agriculture Secretary Dr Wilson Songa, the Kenya Plant Health Inspectorate Service (Kephis) must lead other agencies like the Kenya Wildlife Service, Kenya Forest Research Institute, Ministry of Environment and the National Environment Management Authority to contain the weed.

Kephis managing director James Onsando argued, “It will need a multi-institutional approach with budget implications.

Kephis will initiate the necessary meetings with the relevant institutions.”

Kenya Wildlife Service and CABI are at the forefront of fighting the weed. CABI is a not-for-profit science-based development and information organisation.

KWS has for the first time allocated resources to invasive species management in Kenya and will develop an invasive species strategy.
The weed is in wildlife areas such as the Maasai Mara and around the shores of Lake Elementaita, now a World Heritage Site.
Alarm bells were sounded in mid 2000 by Dr Arne Witt, an invasive species biologist at CABI.

Dr Witt rates parthenium as the worst weed among the top five with the water hyacinth, chromolaena (just starting to invade), prosopis, and cactus species such as Opuntia stricta.

Parthenium has been known to drive peasant farmers to suicide in India and Pakistan because it renders their hands (and often other parts of the body) useless with massive blisters. In some people it aggravates respiratory problems causing asthma and bronchitis.
In livestock, mother goats who have browsed on parthenium produce distasteful milk that even the kids reject.

The plant is also all over Siaya.

Again neither the authorities nor the residents know anything about it.

The minuscule seeds are often a grain contaminant and as such are introduced to new areas through food aid, finding their way into the soil and sprouting even under meagre rainfall. One plant can mature in four to six weeks and produce 10,000-25,000 seeds.

Dr Witt’s survey on Mombasa road three years ago revealed one plant, 50 kilometres east of Nairobi.

Now, strands of the weed are found 200 kilometres west of Nairobi.

“I see many people harvesting grass and other forage for feeding livestock. There is a good chance that it will now become contaminated with parthenium – and large amounts in the collected forage can be fatal to livestock especially sheep and cows,” warns Dr Witt.

She said the potential distribution will be worse in Kenya because of the two rainy seasons each year where the plants grow and produce seeds. It appears that 60 per cent of Kenya has the potential to be invaded — the agriculturally productive areas and areas with high biodiversity such as the Mara and Tsavo. 

This translates into about 348,220 square kilometres of Kenya’s land surface.
In vast areas in Ethiopia, parthenium has turned formerly good agricultural land into green deserts.

“It took about 20 years to invade two million hectares in Ethiopia,” Dr Witt said.

“In Kenya it is in its exponential phase so you will see a doubling in distribution every couple of years. There will be isolated infestations in most areas suitable for spread in about seven years from now.”

It is a frightening scenario. Dr Witt explains the bombshell waiting to explode.

“It will be gradual at first but over 10 years, farmers could lose about 40 per cent of their yield. In pastureland, it will take root in overgrazed areas. The overgrazed areas will be rapidly invaded and will not recover because of the allelopathic (poisonous) chemicals in the plant which render the soil infertile. This will result in higher grazing pressure on uninvaded land resulting in its degradation.”

According to Dr Witt, the water hyacinth pales in comparison with parthenium. Confined to water bodies, the former’s scope of invasion is limited.

But it has a big impact on fishing, water transport and hydroelectricity generation but not directly on agriculture on which 80 per cent of people in Africa are dependent. 

Water hyacinth is also not toxic and animals can eat it if they choose to; neither does it have a direct impact on human health although infestations may provide habitats for malarial mosquitoes and bilharzia transmitting snails.  

On the other hand, mathenge has a massive impact on biodiversity, pasture and water resources and has the ability to spread very quickly.

However, it has some benefits although the costs outweigh any potential benefits — pods but not the leaves can be fed to livestock but not more than 25 per cent in the diet.

The parthenium has no use whatsoever.