By UCCE Rice Farming Systems Advisor Luis Espino 

Overall, 2019 was a year with strong armyworm pressure. In many fields, armyworm densities were high during the tillering stage, requiring a treatment. During the heading stage, densities were low in most fields; however, in several fields, panicle injury was high. 

On average, our moth trapping found that the first moth peak was similar in magnitude than last year’s, about 25 moths/trap/night. However, the first peak in 2019 was a week later than in 2018. We monitored several fields during this time, and infestations only became serious when traps were catching more than 30 moths/night, and the worm population peaked a week after the moth peak. The Intrepid Section 18 was approved earlier than previous years, so growers were able to make treatment decisions early. The heading peak was 12 moths/trap/night; in 2018 this peak was 18 moths/trap/night. Again, the 2019 peak was about a week later than 2018.

Later armyworm infestations should be less problematic than earlier infestations because rice has more foliage and could withstand more defoliation. During the heading stage, fields that were planted early and headed early escaped the most severe armyworm injury that I observed in late planted fields. 

An anomaly observed this year was the population pattern of the western yellowstriped armyworm. In the past four years, the true armyworm has been the species causing problems; while we caught yellowstriped in the pheromone traps, the numbers were low and I did not find any worms in rice fields. This year, yellowstriped numbers in the traps early in the season were high in Colusa and Glenn counties, and then, during heading, high in Colusa and Yolo. I did find some yellowstriped worms in the field during mid tillering, but their density was not high. I’m still puzzled about where these moths are going, and if they are resulting in worm populations.

We will analyze our yearly data and get back to you with some more thoughts during our winter meetings and other outreach events. Thanks to all the growers and PCAs that let us put traps in their fields, Corteva Agriscience for funding, and FarmDog for letting us use their scouting app for free. Also, many thanks to Marcus Rehrman, our Student Assistant that checked all traps weekly even though the AC in the truck is not the best.

Keep updated on this and other important issues by following our UC Rice Blog.