Exploring the mechanisms of winter flooding as a cultural control against rice water weevil, Lissorhoptrus oryzophilus

Rice water weevils (Lissorhoptrus oryzophilus Kuschel) are the primary insect pest in California rice agriculture. They present a challenge for IPM because of their soil dwelling larvae, which prevents the effective use of parasitoids, nematodes and predators. However a possible cultural control method may present a sustainable solution if its mechanism can be explained. Data from the field experiments in the 1990s showed that winter flooding of rice fields to break down post harvest rice straw would result in reduced larval populations in the spring. Studies from the last two years have been exploring the mechanisms behind this decline. Similar results were shown in a greenhouse study in the summer of 2013, with reduced larval counts in treatments with a winter flood compared to treatments without the flood. As part of this study we also examined the addition of rice straw, which nullified the effects of the winter flood. The evidence suggests that  use of winter flooding in California will have benefits for growers against rice water weevil, but the mechanism behind it has yet to be determined.