Delta rice acreage in 2025 continued its upward trend, with yields comparable to the statewide average. Estimates suggest that Delta rice fields approached or surpassed 15,000 acres during the year. The University of California Cooperative Extension (UCCE) collaborated with the California Rice Experiment Station to evaluate commercial varieties and advanced breeding lines, with the San Joaquin County Delta serving as one of eight locations in the statewide trial. Notably, it is the only drill-seeded site and a test location for very-early maturing varieties due to its cooler growing conditions. Results from these trials are expected in February 2026.
Monitoring efforts for true armyworms took place on three Delta farms in 2025. Moth catches peaked around June 30th, similar to observations from 2024 and less severe than years such as 2017, 2018, 2022, and 2023. Trap catches varied between farms and even within fields on the same farm, highlighting the importance of field-level scouting.
Disease incidence appeared low this season. Only one sample was submitted to the UC Davis disease diagnostics lab, which identified aggregate sheath spot. Both aggregate sheath spot and stem rot can be worsened by low potassium levels in soil—a known issue in some Delta soils—making proper plant nutrition an important management strategy. According to UC Rice Specialist Bruce Linquist’s fact sheet, potassium deficiency is indicated if soil extractable K is below 60 ppm; levels between 60 and 120 ppm may benefit from additional fertilizer. Fungicide treatment remains an option if diseases persist despite adequate fertility.
Herbicide resistance testing led by UC Weed Management Specialist Kassim Al-Khatib found barnyardgrass resistance to several herbicides—including Clincher, Regiment, Loyant, SuperWham!—on different farms. Redstems did not show resistance on tested sites. Resistance to Loyant was observed before its commercial use; Postdoctoral Scholar Deniz Inci noted that certain barnyardgrass and watergrass biotypes metabolize Loyant differently, affecting treatment efficacy. Growers are encouraged to observe their herbicide programs’ effectiveness closely and practice label-rate application timing and rotation strategies.
Weedy rice remains present on some Delta farms. UCCE hosted a meeting this summer to share management information with local industry members; presentations are available online at https://ucanr.edu/site/delta-crops-resource-management/meeting-presentations. For affected fields, post-harvest straw chopping without incorporation and winter flooding are recommended practices to help manage weedy rice seed viability.
A project funded by the CDFA Healthy Soils Program and CA Rice Research Board examined cover cropping’s impact on soil carbon and nitrogen dynamics within rice systems where rotations are infrequent. Brassicas emerged quickly but died off under wet conditions; vetches and balansa clover established more slowly but formed vigorous stands by early spring despite moisture challenges.
The report concludes with thanks extended to collaborating growers: “I want to take this opportunity to thank all the growers who collaborated with us on these projects, and I wish everyone a happy harvest season.”
UC Agriculture and Natural Resources (UC ANR), affiliated with the University of California (https://ucanr.edu/), supports agricultural communities through research collaborations like those described above. The organization operates offices in all California counties along with nine Research and Extension Centers (https://ucanr.edu/). It shares science-based practices designed to enhance lives statewide (https://ucanr.edu/) while applying university expertise through outreach initiatives across diverse ecosystems (https://ucanr.edu/). Glenda Humiston serves as vice president of UC ANR (https://ucanr.edu/).