This study investigated the effects of imazamox ammonium salt, fluthiacet-methyl, and bentazon applications for Ipomoea lacunosa L. (pitted morning glory). Field experiments were conducted in narrow-row soybean fields in Hiroshima Prefecture, Japan. The combination of imazamox ammonium salt (0.026 kg a.i. ha⁻¹) application at soybean emergence and bentazone (0.600 kg a.i. ha⁻¹) application on the fifth trifoliate reduced the dry matter weight of I. lacunosa by 94% and controlled common weeds in soybean fields. This control system showed the highest soybean yield in this study. It was considered optimal as a control system for narrow-row soybeans, primarily focusing on controlling I. lacunosa.

The control efficacy of pre-plant soil incorporation of trifluralin emulsifiable concentrate against little-bell morning glory (Ipomoea triloba L.) was evaluated in soybean fields in 2021 and 2022, focusing on the effects of interval between herbicide application and soil incorporation and the degree of weed presence at the time of application. In both years, soil incorporation within 24 hours of application reduced the dry weight (DW) of I. triloba to less than 40% of the untreated control for 2–3 weeks after incorporation, corresponding to the soybean second-leaf stage. Incorporation conducted within 5 hours after application tended to maintain this suppressive effect for over one month. Furthermore, soil incorporation within 2 hours consistently reduced I. triloba DW regardless of weed presence at the time of application. At the soybean second-leaf stage, the leaf number of I. triloba was suppressed to three leaves or fewer, suggesting that early incorporation may enhance and stabilize the efficacy of subsequent foliar-applied herbicides.