I have been trapping armyworms in Delta rice since 2016, after the industry experienced an outbreak in 2015. Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the moths (Figure 1). I have traps at three Delta locations, and at each location, there are three traps that span adjacent fields. We can use trap counts and Growing Degree Day modelling (i.e. a temperature measure of time) to determine whether and when to treat fields. UC IPM provides treatment guidelines, and a Section 18 emergency exemption of methoxyfenozide (Intrepid 2F) has been approved for the 2022 season. (For more information, please contact your county Agricultural Commissioner's office.)
We have begun our 2022 monitoring, and trap counts are higher than they were at this same time last year (Figure 2). (Overall, 2021 was a low-pressure year.) The counts we are observing are not extreme but are on par with what we saw in 2020. It's hard to pinpoint why populations fluctuate from year to year, but it could relate to higher minimum winter temperatures (i.e. better winter survival), and/or migratory patterns from other western states and Canada.
The monitoring that I do in the Delta is part of a larger effort that is spearheaded by my colleague, Luis Espino, rice advisor in Butte and Glenn counties. Luis writes a weekly blog to provide real-time information on trap counts to help growers and consultants with scouting and decision-making. In his blog announcements, he will link to an interactive mapping tool called Ag Pest Monitoring, where you can view counts across trapping locations. Please consider subscribing to Luis Espino's blog, but don't hesitate to reach out to me if you'd like to discuss what is happening in the Delta.
Good luck this season, and I hope to see you in the field!
Figure 1. Bucket traps are placed along field edges. Nine traps are deployed across three Delta locations and are checked weekly. The traps include a pheromone lure that selectively traps true armyworm moths. (Photo by M. Leinfelder-Miles)
Figure 2. 2016-2022 Delta armyworm trap counts. The trap counts represent the number of moths caught per day, averaged across three Delta locations (9 total traps). The 2022 counts are still moderately low, averaging about thirteen moths per day during the week of June 13th, but now is the time to intensify monitoring since peak populations tend to occur between now and early July.