Occurrence of Rottboellia cochinchinensis (Lour.) Clayton in silage corn fields in Tottori Prefecture

Abstract

In the silage corn fields of Kotoura-cho, Tottori Prefecture, the annual grass weed itchgrass (Rottboellia cochinchinensis (Lour.) Clayton), which has rarely been reported in Honshu, is commonly found. The occurrence of this species in the area and its ecological characteristics that affect its establishment were investigated. The occurrence of itchgrass was confirmed in 210 silage corn fields, with an occurrence rate of 33.1%. Seedling emergence of itchgrass was observed in the field from mid-April, and heading began from late June to late July. By early August, when corn harvesting begins, seed-shedding began. In pot experiments, relatively many seeds sown on the soil surface in September emerged within the year, with 1.3–36.7% emerging the following year. When incorporated within the soil, the seed survival rate was higher than when surface-sown, with 24.0–57.5% emerging the following year. The plants planted in pots on May 3rd headed in early July, and those planted on July 6th headed in late August, and both produced mature seeds. However, the plants planted on September 8th headed in late November but failed to produce mature seeds. Itchgrass has ecological characteristics that allow it to colonize in silage corn fields in Tottori Prefecture, and it is considered a weed species whose invasion should be monitored carefully in temperate regions.