Defoliators: Cutworms and Armyworms in Small Rice

by Jarrod Hardke, Rice Extension Agronomist - May 9, 2023

Defoliators: Cutworms and Armyworms in Small Rice

Nick Bateman, Ben Thrash, Glenn Studebaker, and Jarrod Hardke

A few weeks ago, we mentioned seeing some true armyworms in wheat and the possibility of them moving into rice.  Over the past week, we have gotten several calls on this.  We have also had numerous calls on cutworms in rice, soybean, and corn.  The cutworm calls seem to be outweighing the armyworm calls at the moment.

In general, true armyworms tend to “march” across a field, eating the rice back to ground level and moving to the next plant.  Cutworm feeding tends to be more sporadic throughout the field.  Cutworms are more prone to be in fields with old crop residue or standing stubble compared to a clean field.  If you are seeing clipped off plants, you can usually look under the stubble or down in the cracks near the plants and find the worms.

Recommendations for both pests are the same.  We generally don’t recommend treating small rice for defoliation.  We have done several years of work on this, and just do not see a yield loss from defoliation occurring through early tillering (Figures 1 & 2).  In a lot of cases, we see a minor yield increase.  With that said, there are always exceptions to thresholds.  If feeding is occurring on the growing point, below ground at the seed, due to soil cracking then an application should be considered.  If the caterpillars can feed down to the seed, they will kill the growing point and ultimately the plant.  Plants that have been eaten down to ground level or clipped off at the ground will regrow – in a couple weeks the area usually catches up with unaffected rice.

For insecticide options, if you are in a situation where you need to spray, we would suggest sticking to lambda-cyhalothrin products (Warrior II, Lambda-Cy, etc.).  It’s recommended that these applications be made very early morning or late evening since most of the feeding will occur at night.  If you have Dermacor or Fortenza as a seed treatment, then they should protect the rice with no issues.  These seed treatments don’t stop all feeding damage – the insects do have to eat some to be exposed to the insecticide.

Clipped rice plants from cutworms.

Photo Credit: Scott Greenwalt, Nutrien Ag

Black cutworm in small rice with clipped off plants.

Photo Credit: Scott Greenwalt, Nutrien Ag

Black cutworm feeding on small rice.

Photo Credit: Stewart Runsick, UADA

Figure 1. Yield compared to the untreated control for multiple defoliation levels and growth stages for April planted rice.

Figure 2. Yield compared to the untreated control for multiple defoliation levels and growth stages for May planted rice.

Additional Information

Arkansas Rice Updates are published periodically to provide timely information and recommendations for rice production in Arkansas.  If you would like to be added to this email list, please send your request to rice@uada.edu.

This information will also be posted to the Arkansas Row Crops blog (http://www.arkansas-crops.com/) where additional information from Extension specialists can be found.

More information on rice production, including access to all publications and reports, can be found at http://www.uaex.uada.edu/rice.

Acknowledgements

We sincerely appreciate the support for this publication provided by the rice farmers of Arkansas and administered by the Arkansas Rice Research and Promotion Board.

The authors greatly appreciate the feedback and contributions of all growers, county agents, consultants, and rice industry stakeholders.