Time to think about rice water weevil management
By Jeff Gore, Research and Extension Entomologist, Bobby Golden, Agronomist, Delta REC, Mississippi State University, Jason Bond, Research/Extension Weed Scientist, Tom Allen, Extension Plant Pathologist and Don Cook, Research Entomologist, Mississippi State University
A little rice has started to go to flood in Mississippi this week and that means it is time to start thinking about rice water weevil. Overall, the majority of the crop is behind because of all of the rain that we have had across the Delta over the last several weeks. In general, the rice that is currently being flooded was some of the earliest planted. As a result, the early rice has endured a lot of rainfall and adverse conditions.
The environmental conditions through March and April, especially the heavy rain between planting and now, were not ideal for performance of insecticide seed treatments. We recently had a graduate student, Mr. Andrew Adams, that finished his research looking at the time from planting to flood and flushes on the performance of seed treatments. He delayed the flood out to 8 weeks after planting and showed that it did not negatively impact rice water weevil control.
In contrast, flushing the field at least 2 times reduced rice water weevil control. Basically what his research showed was that the seed treatments did not perform as well when he flushed the field 2 times as they did when he did not flush the field or when he flushed the field 1 time. This was reflected in both weevil numbers and yields. Although flushing is not the same as rain, this does provide an indication that the seed treatments may not perform as well as we would like them to.
The bottom line is that it will be important to scout fields closely for feeding by adult weevils, especially in fields that have experienced a lot of rainfall. If excessive adult feeding is observed, a supplemental foliar insecticide may be warranted, even where a seed treatment was used. In fields where a seed treatment was used, a pyrethroid will likely be the most economical option. In fields where no insecticide seed treatment was used, a pyrethroid should do a good job if timed properly.
In some situations on untreated rice, Belay may be a better option. We have looked at Belay for the last two years and found that timing is less important than with pyrethroids. We presume that this is the case because clothianidin, the active ingredient in Belay, is systemic. Our research showed that it provided similar control to the pyrethroids, but was much more consistent in terms of control and yield protection on rice that did not have a seed treatment at planting.
Our results over the last several years have shown that yield losses are directly correlated with rice water weevil larval numbers. Regardless of whether a seed treatment was used or not, it is important to maximize rice water weevil control as fields are flooded to prevent yield losses.