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4. Zambia: Control measures target destructive weed (Inter Press Service)

Control measures are underway to attack an invasive weed that has reportedly taken over almost 3,000 hectares of pasture in one of Zambia’s wetland areas, known as the Kafue Flats.

Originally from Mexico, the Mimosa pigra weed thrives on the fringes of floodplains and near dams. In the Kafue Flats, these same conditions have traditionally fostered the growth of indigenous plants that provide pasture to livestock and wild animals. But since the 1980s, Mimosa pigra has covered more and more pasture with dense thickets.

Highvie Hamududu is a member of parliament who represents part of the area affected by the weed. He said that urgent action is needed to keep grazing lands accessible to animals.

It is believed that a steady decrease in rainfall in the Kafue Flats has promoted the growth of the weed by limiting seasonal flooding. The construction of dams on either end of the floodplain has also made conditions more favourable to the weed.

Once the weed is established over a large area, intensive measures such as aerial spraying of herbicides are needed to curb or reduce its spread. A coalition of parties concerned about Mimosa pigra’s spread in the Kafue Flats says it cleared 100 hectares of the weed this year and plans to clear 1,000 hectares over the next two years.

Mimosa pigra is considered one of the world’s most invasive species, and has created problems for herdsmen in many countries. Ethiopia, Ghana, and Uganda have all faced the challenge of controlling the weed.

Fortunately, small infestations are relatively easy to control. Farmers and herdsmen can dig up individual plants and burn them, taking special care to remove as much of the root structure as possible. The area where the weed was found should be checked regularly for re-growth.

Mimosa pigra is a thorny shrub that grows between two and six metres high. It has green stems that become woody as it matures and fern-like green leaves that fold together at night or when touched. The Mimosa pigra flower is pink-purple in colour and 10 to 20 millimetres wide.