Killer weed invades farms, grazing lands and national parks

Just like hyacinth in the early 1990s, and Striga weed a decade later, the Parthenium hysterophorusa weed which “sneaked” into the country a few years ago threatens to hurt the flora and fauna if its spread is not curtailed.

There are fears that unless the government acts immediately, the Parthenium hysterophorusa, a noxious weed now spreading alarmingly in several parts of the country, will reduce agricultural and livestock productivity, and seriously affect wildlife.

At great risk from the weed also known as Santa Maria feverfew, are farmlands, grazing fields, national parks and game reserves. The weed multiplies and spreads fast, while inhibiting other underground growth.

According to the director of Agriculture, Mr Humphrey Mwangi, the weed is alarmingly sprouting in several places within the short period it has been noted.

Mr Mwangi said of the weed which came into the limelight early last year: “The weed was designated by agricultural authorities in the Ministry of Agriculture as plants that are injurious to agricultural crops because they grow aggressively, multiply quickly and adversely affect desirable plants’ qualities.”

The director noted that the weed had limited distribution but had the potential of becoming more widespread and cause impact on agriculture as well as human health and environment. The potential adverse impact of the weed exceeded far beyond the cost of implementing the control measures, he said.

Ms Triza Karanja a pathology and weeds officer at the ministry said the impact on the noxious weed was reduction in agricultural yields and grain weight. It also acts as alternate host to crop pests.

According to Ms Karanja, there was also an enormous impact on animal husbandry where the Parthenium weed could reduce pasture carrying capacity by up to 90 per cent.

“The problem with the weed is that it colonises the other underground plants and becomes the dominant weed, therefore inhibiting the growth of grazing grass which eventually leads to loss of pasture,” said Mr Karanja.

She said the weed was abundant in Nairobi and infestations have been seen in villages in Kiambu, Nyeri, Narok, and towns along the main road from Mombasa to the Ugandan border town of Busia.

Invasive species

Other serious dangers have been raised over the growth of the weed in game reserves and national parks. Maasai Mara ecosystem in Kenya which hosts the largest wildlife migration known to man has not been spared the attack by the noxious weed.

According to researchers, the weed originally from Central America has been found growing along parts of the Mara river and along some dirt tracks in Maasai Mara National Reserve.

Dr Arne Witt, an invasive species coordinator at the Centre for Agriculture and Bio-Sciences International (CABI) Africa said although the weed may look benign to most people, it probably posed one of the most serious threats to the ecosystem.

“Research suggests that conditions in the Maasai Mara are highly suitable for this weed so we should all be very concerned,” said Dr Witt. Parthenium had gained notoriety in Australia, India and Ethiopia where it was accidentally introduced.

The weed can grow from seed to maturity in 4-6 weeks and has an ability to produce 10,000–25,000 seeds; it produces chemicals which inhibit the growth of other plants.

To the researchers, this meant that if it invaded natural pasture, it could reduce the amount of available forage to such an extent that carrying capacities of grazing animals could be reduced by up to 90 per cent.

Fatal consequences