Invasion of the killer weed from South America

It looks nondescript. A plant with tiny white flowers. Yet the plant, parthenium, has the potential to create a pandemic that can destroy Kenya’s agricultural yields by up to 40 per cent, reduce pasture by up to 90 per cent and impact negatively on human health.

“In 50 years, the whole of East Africa could be drowning in a sea of invasive species,” warns Arne Witt, an invasion biologist at CABI, a not-for-profit science-based development and information organisation.

The organisation helps improve people’s lives by providing information and applying scientific expertise to solve problems in agriculture and the environment.

Parthenium originates from Central and South America. It is a weed but because it has an array of local insects that forage on it in its homeland, the plant is kept in check.

On new continents where the climate is similar but with no insects to feed on the weed, it is having a field day edging out the local flora to the extent of becoming a threat to them.

In the past five years, this weed has exploded in Kenya, and is now common along the edges of the Nairobi National Park, Mlolongo and Athi plains.

Its historical route into Africa follows that of food aid brought in by foreign agencies in war-torn and drought stricken countries.

First recorded in Ethiopia in the 1980s, it is now present in Uganda, Tanzania, Swaziland, Mozambique, Zimbabwe, Somalia and South Africa.

The grain route

It could be in other African countries but because there aren’t many people studying it, its full extent is not known.

The weed is often associated with places where food aid is distributed. During times of drought, Kenya is one of the largest importers of food in Africa.

“It’s a seed contaminant,” says Witt. He has been studying the invasive species since his student days at a South African university in the 1980s. South Africa has more than 300 recorded species of invasive plants.

Parthenium grows on farmed land — including wheat and maize fields.

Often, when the grain is harvested, so are the miniscule seeds of parthenium, which are then transported with the grain to other regions.

Once in Africa and free of natural enemies, the plant grows unchecked, just like the infamous water hyacinth — also from South America — now a major problem in the region’s fresh water lakes.