I have been trapping armyworms in Delta rice since 2016, in collaboration with my colleague in the Sacramento Valley, Luis Espino. Monitoring involves scouting for worm damage – like leaf feeding or panicle injury – and deployment of pheromone bucket traps that catch the moths. The worms are often difficult to find unless you are scouting early in the morning before it gets too hot, which is why we use the pheromone bucket traps. We can observe when moth populations are reaching their peak to inform treatment decisions. Over the years, UCCE has cooperated with the California Rice Commission to get Section 18 emergency approvals of methoxyfenozide (Intrepid 2F), and because we have trapping data from the Delta, San Joaquin County has been included on the approval. Thank you to the cooperating growers for allowing me to trap on their farms.

In previous years, we trapped for both true armyworms and western yellowstriped armyworms. It appears, however, that the true armyworms are the ones that damage rice, so this year, we focused our trapping on them. I trap on three islands in the Delta, and I did see some leaf feeding damage in June. Moth flights peaked in late June (Fig. 1), but overall, damage was not severe this year. In fact, the moth counts were the lowest that I have seen since I started trapping in 2016. Some growers indicated needing to spray, but others did not. For those who sprayed, populations fell and did not resurge later in the season. I saw very little, if any, panicle injury in August and September.

You can find more information about my Delta rice research and extension program on my website. I wish you a successful harvest season!

 

Figure 1. Delta true armyworm trap counts. The trap counts represent the number of moths caught per day, averaged across three Delta locations. The 2021 counts were the lowest seen since trapping began in 2016.