I have been monitoring some fields in the Glenn and Butte County area the past two week and I have been finding some significant number of armyworms. Defoliation is not noticeable yet, at least not just by looking at the canopy. If you look under the canopy you may see some defoliation. The worms are still small but I have been finding 5 or more worms per square foot. Past research has shown that more than 5 worms per square foot can result in defoliation exceeding 25%.

Armyworms found on June 28, 2024, Butte County

Boxplot of number of larvae per square foot found causing defoliation in seven locations of the Sacramento Valley of California, 2022 and 2023. Numbers above boxes correspond to the number of observations of that level of defoliation. 

Make sure you scout your fields closely this upcoming week. Early next week we will know if we are at peak moth flight, which would mean that next week is when we expect the most worm activity.