Suppression of entireleaf morning glory (Ipomoea hederacea Jacq. var. integriuscula A. Gray) growth by lawngrass (Zoysia japonica Steud.) on soybean field levees in southwestern Japan

The spread of morning glory (Ipomoea spp.) in Japanese soybean (Glycine max (L.) Merr.) fields has severely decreased soybean yields. Field levees are believed to be a source of this invasion. The introduction of Zoysia japonica Steud. is expected to suppress weed growth and reduce the required labor for weed management on the levees. In this study, field experiments were conducted on the soybean levees of turf (Z. japonica), bare, and weed (mainly broad leaf weeds such as white clover) from 2017 to 2019 to compare its effects on the occurrence, growth, and seed production of I. hederacea (L.) Jacq. var. integriuscula A. Gray. The canopy height in the turf levee was the lowest, and the vegetation cover rate was the highest. At the flowering and fruiting stage of I. hederacea var. integriuscula (September), the largest number of I. hederacea var. integriuscula that survived were on the turf levee; however, the plant length, dry weight, and the number of fruits were the least. Additionally, the stems of the morning glory on the turf levee were slight and spindly, and their growth and seed productivity were suppressed. Consequently, vegetation conversion to Z. japonica on the soybean field levees can be an effective strategy to suppress the colonization and growth of morning glory, thereby, improving soybean yields.