MSU study: Rice water weevil densities vary within a row-rice field

• By Jeff Gore and Dan Roach •

MSU grad student read kelly

MSU graduate student Read Kelly counts rice water weevil larvae from a core sample — photo courtesy Mississippi State University

Read Kelly, a graduate student under the direction of Jeff Gore, has been investigating the relationship and densities of rice water weevils in furrow-irrigated or row rice.

During 2017 and 2018, Kelly conducted rice water weevil studies on 11 on-farm sites across the Mississippi Delta. Each location had a furrow-irrigated field compared to an adjacent conventional flooded field using the alternate wetting and drying, or AWD, irrigation method.

As stated in previous articles, furrow-irrigated rice fields are actually three sub-fields.

The top one-third is the driest, the middle is similar to the optimized AWD treatments (soupy wet but never dry) and the bottom one-third resembles a continuous-irrigated field.

Kelly collected core samples for water weevil larvae in each of the furrow-irrigated zones as well as the conventional AWD comparison field.

Here are Kelly’s results: 

1. Rice water weevil densities were moderate and increased each week in the flooded portion of the fields.

2. Rice water weevil densities were similar in the conventional field and the flooded lower one-third of the furrow irrigated field.

3. Rice water weevil densities were the lowest the the top two-thirds of the furrow irrigated fields.

4. Overall rice water weevil densities were lower in the furrow irrigated fields compared to the conventional AWD comparison

This study suggests that growers could adjust their management style for rice water weevils in furrow-irrigated fields. In general, insecticide seed treatments such as Cruiser or NipsIt are still recommended across the whole field, especially in fields with a history of other pests such as chinch bugs.

Foliar applications targeting rice water weevil adults can usually be confined to the lower third of row-rice fields where rice water weevil densities will be greatest.

Dr. Jeff Gore is a research and Extension entomologist at the Mississippi State University Delta Research and Extension Center in Stoneville. He may be reached at jg231@msstate.edu. Dan Roach is an Extension associate at the DREC.