Saga City officials are piloting a biological control method using a Chinese culinary vegetable to suppress an invasive aquatic plant [1, 2].

This experiment aims to prevent urban flooding by clearing drainage canals. The invasive plant, known as Nagaetsuru no Geitou, forms dense mats that block water flow, which increases the risk of overflow during heavy rainfall [2, 3].

Mayor Sakai Hidetaka announced the trial on June 18, and said the city is starting a new demonstration experiment against the water weed [1]. The plant is often referred to as the worst invasive plant on Earth [1]. To combat its spread, the city is utilizing Kousinsai, a vegetable common in Chinese cuisine, to suppress the growth of the invasive species [1].

Fukuda Kunihito, the deputy director of the Saga City Agricultural Environment Division, said the plant has overgrown the water's surface. He said that when it reaches this level of growth, it significantly hinders drainage and prevents smooth water flow during heavy rain [2].

The struggle against the weed is a long-term challenge for the region. Nagaetsuru no Geitou was first recorded in Japan in 1989 in Hyogo Prefecture [2]. Despite efforts to clean the canals, the plant typically reappears within approximately one year [2].

City officials are testing the method in both agricultural irrigation canals and a municipal drainage ditch located in a residential area [1, 2]. While a recent typhoon did not cause major damage, officials said that water flow was impeded by the vegetation [2]. Mayor Sakai said the demonstration experiment using the culinary vegetable is expected to potentially inhibit the reproduction of the invasive plant [1].

“The plant is often referred to as the worst invasive plant on Earth.”

The use of a competitive plant species like Kousinsai represents a shift toward biological control to manage infrastructure risks. By introducing a non-invasive but competitive vegetable, the city hopes to create a sustainable barrier that reduces the labor and cost of annual mechanical dredging while mitigating the flood risks associated with Japan's increasingly volatile weather patterns.