Use of pheromone traps to monitor for armyworms, <i>Mythimna unipuncta</i> (Lepidoptera: Noctuidae), in California rice

Armyworm, Mythimna unipuncta (Haworth), moth populations were monitored using pheromone traps in 15 rice fields in the Sacramento Valley and three rice fields in San Joaquin County, California, between 2018 and 2023. Larval populations were monitored in four to seven rice fields in the Sacramento Valley between 2021 and 2023 by searching 10 min or 0.3 m2. Two moth flights and two larval generations were observed. Analysis of covariance showed larval numbers were related to moth numbers caught in the traps 1 to 2 wk earlier, but this relationship varied between fields. The week when the first moth peak occurred was similar across locations while the week when the second peak occurred was more variable. Results indicate that in the Sacramento Valley armyworm pheromone traps can be used to identify periods of peak larval density during which monitoring can be intensified to determine if larval injury will reach the economic threshold.