Delayed flood timing and rice cultivar influence infestations of rice water weevil and Mexican rice borer in drill-seeded rice

Rice water weevil, Lissorhoptrus oryzophilus, is the most important early-season pest of rice in the U.S. Additionally, lepidopteran stem-boring pests particularly the invasive Mexican rice borer, Eoreuma loftini, are increasingly becoming problematic in Louisiana rice. This study was conducted to evaluate the effects of flood timing and rice cultivar on weevil and stemborer infestations. Field experiments were conducted in Louisiana from 2019–2020. In each year, early- and late-planted trials were established according to a split-split-plot RBD. Four commonly grown rice cultivars were selected and were either treated or not treated with a chlorantraniliprole seed treatment. Permanent flood was established at normal timing (five-leaf stage) or delayed by two weeks. Seed treatment reduced weevil densities and stemborer injury by 70–84% and 87–94%, respectively. The cultivar ‘Jupiter’ supported the highest numbers of immature weevils, whereas low levels of stemborer injury were observed in ‘Jazzman-2’. Weevil densities were 72% and 20% lower in plots subjected to delayed flood in the 2019 and 2020 late-planted trials, respectively. Reductions of 79% and 93% in stemborer injury in the 2019 early- and late-planted trials, respectively, were observed in delayed flooded plots. Both pests negatively affected rice yields, with losses ranging from 14–49%. Losses were low in plots subjected to delayed flood but the difference was only significant in the 2020 late-planted trial. Our data suggest that the combination of cultivar resistance and flood timing can serve as a valuable component of an IPM program for both pests.