Abstract
The rice water weevil, Lissorhoptrus oryzophilus Kuschel, 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 (Dyar), are increasingly becoming problematic in Louisiana rice. Although insecticidal seed treatments have been widely adopted and have proven highly effective against weevils and stemborers, alternative management tactics are needed. This study was conducted to evaluate the effects of flood timing and rice cultivar on rice water weevil and stemborer infestations. Field experiments were conducted in Crowley, Louisiana, from 2019–2020. In each year, early- and late-planted trials were established according to a split-split-plot randomized block design. 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 (approximately the five-leaf stage) or delayed by 2 weeks. Seed treatment reduced weevil densities and stemborer injury by 70–84% and 87–94%, respectively, across planting dates, years, cultivars, and flood timings. The rice cultivar ‘Jupiter' consistently 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 compared to normal flood timing 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. Weevil and stemborer infestations negatively affected rice yields, with losses among cultivars ranging from 14 to 49%. Yield losses were generally lower in plots subjected to delayed flood compared to normal flood timing but the difference was only significant in the 2020 late-planted trial. Our data suggest that the combination of cultivar resistance and delayed flooding can serve as a valuable component of an integrated pest management program for both rice water weevil and stemborers.
Highlights
Rice, Oryza sativa L., is one of the most important crops globally and is consumed by more than half of the world’s population (Mohanty, 2013)
This study examines alternative tactics to insecticidal seed treatments for managing infestations of rice water weevils and stemborers
The results from the experiments presented here demonstrate that rice cultivars vary in their susceptibility to infestations by rice water weevil and Mexican rice borer, and delaying flood application by only 2 weeks can reduce infestations and impact of these insect pests
Summary
Oryza sativa L., is one of the most important crops globally and is consumed by more than half of the world’s population (Mohanty, 2013). Adult weevils overwinter in leaf litter, bunch grasses, and stubble in and around rice fields and typically emerge from overwintering in early spring (Shang et al, 2004). Injury from adult feeding is generally not considered economically important except under unusually heavy infestations (Stout et al, 2013). The establishment of permanent flood in rice fields triggers female weevils to lay eggs in rice leaf sheaths beneath the water surface (Stout et al, 2002b). The majority of economic loss is caused by the soildwelling, root-feeding weevil larvae which cause extensive injury to rice root systems, resulting in reductions in tiller numbers, grain weights, and grains per panicle (Shang et al, 2004; Zou et al, 2004a). Yield losses can exceed 25% if rice water weevil infestations are left unmanaged (Stout et al, 2000)
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