HYOGO, Aug 25, 2025 (News On Japan) - Rice paddies in Hyogo Prefecture are coming into harvest with a new threat on their margins: dense mats of the designated invasive species known in Japan as Nagaetsurunogeitou. Often described as one of the world’s worst invasive plants, the aquatic weed invades irrigation ponds and canals, saps nutrients, and wraps around rice stems, hindering growth.
Officials and farmers say the plant is highly adaptable, thriving both in water and on land and showing strong resistance to drying.
The weed’s explosive spread has clogged drainage pumps and at times forced large-scale removal by boat. As of July, reports of Nagaetsurunogeitou had expanded to 29 prefectures, straining local responses. In southern Hyogo, a reservoir supplying water to about 180 hectares of paddies has become a frontline. Crews lay light-blocking sheets across infested surfaces to suppress growth, but shoots push through tiny gaps within a month, turning weed control into a relentless cat-and-mouse battle.
A separate designated invasive species is threatening the prefecture’s beloved cherry trees. At Ishitani Park in Hyogo—famous for spring blossoms—protective netting now wraps the bases of trunks to keep out the red-necked longhorn beetle, an insect native to parts of China and elsewhere. Once the larvae bore in, they hollow the interior, weakening trees to the point that felling may be the only option to prevent collapse. The beetle’s prolific reproduction, with females laying roughly 500 to as many as 1,000 eggs, is accelerating the spread.
In August, Hyogo Prefecture established a Special Invasive Species Task Force to map the expanding distribution of these pests and step up measures. With risks ranging from reduced rice yields to the loss of cherry trees in public spaces, authorities are urging swift, sustained efforts to contain further damage to agriculture, ecosystems, and daily life.
Source: YOMIURI
