Impact of planting date on rice water weevil (Coleoptera: Curculionidae) and stemborer (Lepidoptera: Crambidae) infestations in drill-seeded rice.

The rice water weevil, Lissorhoptrus oryzophilus (Kuschel), is the most widely distributed and destructive early-season pest of rice in the United States. Injury caused by feeding of weevil larvae on rice roots results in significant yield losses. In Louisiana, a complex of stem-boring lepidopteran pests also attacks rice. Of this complex, the Mexican rice borer, Eoreuma loftini (Dyar), has recently invaded Louisiana and now poses a consistent threat to rice production. To study the effects of planting date on rice water weevil density and stem borer damage (whiteheads), field experiments were conducted in Louisiana from 2018 to 2020. Six rice cultivars (CL152, Cheniere, Cocodrie, Jazzman-2, Jupiter, and PVL01) were drill-planted in small plots across 6 planting date ranges per year. Weevil densities on rice roots were evaluated 3 and 4 weeks after permanent flood establishment, and stem borer infestations were assessed by recording the total number of whiteheads in each plot at 100% heading. At grain maturity, entire plots were harvested. Weevil infestation levels remained high throughout all planting dates; however, densities were slightly lower in the later planting dates. The rice cultivar 'Jupiter' supported higher weevil densities compared to 'Cheniere'. Whitehead densities increased with later planting. The rice cultivar 'PVL01' consistently had the highest number of whiteheads. In addition, yields were lower at late planting dates. Results from this study suggest that rice water weevil poses a consistent threat throughout the range of typical planting dates, whereas the stem borer incidence tends to become more problematic in later-planted rice.