Paddy cultivation under giant threat

by Jagath Kanaherarachchi

Environmentalists have warned that low lands and abandoned paddy fields in the Western Province are under threat of being encroached upon by the invasive plant Yoda Nidikumba soon.

The aggressive invasive plant known as the Giant Mimosa (Mimosa pigra) has been identified as a significant threat, with the potential to spread across low-lying areas, including paddy fields in the Western Province over the next few years.

This plant causes severe impact on biodiversity, agriculture, and human activities. It was previously concentrated in the Central Province, particularly around the Mahaweli River and other waterways. However, it is now rapidly spreading into the Western Province, according to environmentalists.

The Giant Mimosa is taking over abandoned sections of the Central Expressway, particularly in the Kadawatha-Mirigama stretch.

Giant Mimosa at Central Highway construction site in Daraluwa

Unlike other Mimosa species found in Sri Lanka, such as Mimosa pudica (Medicinal Mimosa) and Mimosa invisa, the Giant Mimosa (Mimosa pigra) is an exotic, highly invasive species. It has been listed among the top 20 invasive plants in Sri Lanka.

First identified in 1995 at Tennekumbura in Kandy by agricultural scientists Senior Prof Buddhi Marambe of the Agricultural Faculty of the Peradeniya University and Dr. Lakshman Amarasinha, former Director of the Field Crops Research and Development Institute at the Department of Agriculture, the plant has since become a growing concern.

When asked about the rapid spread of the Giant Mimosa in the Western Province, Professor Marambe said that the Ministry of Environment, the Central Environmental Authority, and provincial agricultural and environmental institutions had to take urgent action to neutralise the threat.

“In 2002, our survey in the Central Province revealed that 474 acres were infested with this plant. The current situation may be even worse. The issue is that even if we eradicate all existing plants, the seeds of this species can remain viable for 23 to 50 years, meaning the plant could re-emerge anywhere in Sri Lanka. Additionally, the seeds spread through water, posing a significant risk to paddy fields and wetlands,” Professor Marambe said.

He also warned that the extensive wetlands along the Attanagalu Oya, including areas in Gampaha-Daraluwa, which are frequently flooded, could soon fall victim to the Giant Mimosa invasion.