We have begun seasonal monitoring for armyworms in rice. Our monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the true armyworm moths. Traps are set-up at three Delta locations, where at each location, there are three traps that span adjacent fields. The traps are checked weekly, and monitoring data since 2016 are depicted in Figure 1. The large blue arrow indicates the population trend line this year after the first week of trapping. Data are expressed as moths caught per day, averaged across all nine Delta traps. The data allow us to visualize how the population is tracking within the season and compared to previous years.
It is important to pair the monitoring data with observations in the field. Scouting should occur in the early morning hours. In the heat of the day, larvae recede into the canopy near the water line and are difficult to find, particularly the early instars. UC IPM provides treatment guidelines that include damage assessments and signs of the worms in the field. At the foliar stage, if at least 25 percent defoliation from feeding is observed, and worms are visible, then treatment may be warranted. UC IPM offers this procedure:
To monitor, choose a part of the field where you have observed injury. Walk into the field and inspect plants in a small area around you from the water level to the top of the leaves. Check the water surface for armyworms that may drop from the plants. Determine if 25% or more of the foliage has been removed by armyworms and if they are still present. Record your observations. Repeat this procedure every 5 to 10 feet across a transect until 10 stops have been examined. Repeat this procedure in several areas of the field to create a confident estimate of the average field condition.
At the panicle stage, if 10 percent of the panicles are damaged and worms are present, then treatment may be warranted. I want to emphasize that field monitoring is an important part of armyworm management. Do not rely on the trapping data alone because there is variability across farms and even across fields on the same farm.
Armyworm larvae will grow to full size and pupate in about 3 to 4 weeks. We have learned over years of trapping that when moth flights peak (usually in early July), that if treatment is warranted, the treatment is most effective if applied in the week or two after the peak moth population. While in the Sacramento Valley, a second peak may be observed in August, we have not observed a second, August peak in the Delta.
Over the season, I will be connecting with the rice farming community to communicate ‘real-time’ monitoring data to help advise management. Anyone who has questions about rice armyworm management, or who wants to be included in ‘real-time’ monitoring communications should reach out to me promptly so that I can update my contact list. I will post a blog summary of the seasonal data in the fall, along with a recap of Delta rice research. Good luck this season!
