Effects of differences in biological characteristics between Ipomoea coccinea and I. lacunosa on control of new selective post-emergence herbicides

Summary In Japan, the spread of morning glory ( Ipomoea spp.) in soybean fields has become a serious problem. The aims of this study were to elucidate the biological characteristics of red morning glory ( I. coccinea L.) and pitted morning glory ( I. lacunosa L.) as well as to investigate the control effects of an application system with fluthiacet-methyl and imazamox ammonium salt. Field experi ments were conducted from 2019 to 2020 in Higashi-Hiroshima city, Hiroshima Pref., Japan. The cumulative emergence rate of the pitted morning glory increased earlier than that of the red morning glory. The cumulative emergence rate of the red morning glory and the pitted morning glory reached 90% at 16 to 27 days and 10 to 14 days after soybean sowing, respectively. In addition, for the pitted morning glory, the rate of leaf age development was higher than that of the red morning glory. The morning glory vines also devel oped earlier, and the initial growth tended to occur earlier in the season than in the red morning glory. In the application plots for the selective post-emergence herbicides, a negative correlation was found between dry matter weight of the pitted morning glory and the number of soybean seedlings. In contrast, a positive correlation was found between the dry matter weight of the pitted morning glory and the relative photosynthetic photon flux density in the soybean canopy. Therefore, to enhance the control effect of the pitted morning glory by selective post-emergence herbicides, it is important to increase the number of soybean seedlings and the effect of shade by promoting soybean growth.