Ipomoea cairica and Pomacea canaliculata are invasive species that are very harmful to natural and artificial ecosystems and rice production in Southern China. Ipomoea cairica, a perennial herbaceous liana, is a highly invasive climbing plant. Pomacea canaliculata is a common freshwater snail that is especially abundant in water irrigation systems of paddy fields and in local wetlands. This snail feeds on the young stems and leaves of paddy, causing extensive damage. Therefore, it threatens the integrity of the rice bowl and the security of farmers and workers that rely on rice as their main staple food and source of income. Because of its extensive reproductive capacity and the substantial damage it causes to rice fields, P. canaliculata is classified as one of the 100 worst invasive pest species worldwide. Many methods have been developed and used to control P. canaliculata, the most common of which are chemical control methods. However, because of the long-term use of chemical molluscicides in some areas, snails have developed resistance to these chemicals. Therefore, new methods of biological control should be explored to control this pest. The aim of the present study was to investigate the toxic effects of substances produced by I. cairica on this pest, and on its host crops. The ethanol extract from I. cairica showed toxic effects against P. canaliculata. Previous studies have shown that coumarins are substances that are toxic to schistosome host snails. The aerial parts of I. cairica contain the coumarins umbelliferone (UMB) and scopoletin (SCO). Previous studies have shown that UMB has toxic effects against the fifth instar larva of Pierisrapae linne, and that SCO functions as a neurotoxin. We evaluated the UMB and SCO contents in different organs of I. cairica and in samples of I. cairica collected in different seasons by HPLC analysis. The highest concentrations of both UMB and SCO in I. cairica were in samples collected in summer, followed by those collected in spring, autumn, and winter. In each season, the concentration of SCO was higher than that of UMB. In summer, there were higher SCO concentrations in stems, but in autumn and winter, SCO was distributed in young leaves and stems. We evaluated the toxic effects of UMB and SCO against P. canaliculata, and found that at the same concentrations, UMB had a stronger toxic effect than SCO. At a concentration of 200 μg/mL, UMB killed 100% of P. canaliculata in 24 h, but SCO killed only 8% of P. canaliculata in the same time period. We evaluated the effects of UMB and SCO on growth of rice and barnyard grass seedlings in a pot experiment. The effects of SCO on growth of rice and barnyard grass were stronger than those of UMB at the same concentration. Both UMB and SCO promoted seedling growth when applied at concentrations of 50 and 100 μg/mL, but inhibited seedling growth when applied at concentrations of 200 and 400 μg/mL. When applied in combination, UMB and SCO had stronger effects on the growth of rice and barnyard grass and on P. canaliculata than either compound applied singly at the same concentration. Both UMB and SCO were well-degraded within 10 days in soil. The ecological functions of UMB and SCO in I. cairica plants deserve further investigation.