Optimum Mechanical Treatment Month for Aquatic Plant Control in the Ninoseki Irrigation Channel

Abstract

Growth of aquatic plants to physically large sizes can cause a decline in waterway areas and negatively impact scenic views. We determined optimum mechanical treatment month for aquatic plant control, of a colony consisting mainly of Elodea nuttallii, in an irrigation channel located in the Tohoku region of northern Japan. We removed aquatic plants using an engine-powered water jet in early August and mid-September and observed aquatic plant colony heights and surface aquatic plant varieties. We set up 4 test blocks, each of which consisted 48 monitoring stations and analyzed by comparing test blocks. Early August treatments did not show significant effects, since treated colony heights were similar to those of untreated blocks. However, colony heights did not reach the water surface and thus did not cause scenery deterioration. If aquatic plants do not grow rapidly enough to reach the water surface, mid-September treatments could be skipped. Conversely, mid-September treatments could effectively reduce October colony heights.