Delta rice acreage has been steadily increasing, and yields are comparable with the statewide average. I estimate that acreage approached, if not exceeded, 15,000 acres in 2024. This article is my seasonal update on UCCE Delta rice research and observations.

Table 1. Rice acreage and yield. 

Variety Trial: UCCE collaborates with the California Rice Experiment Station to evaluate commercial varieties and advanced breeding lines. The San Joaquin County Delta was one of eight locations in the 2024 statewide trial. The Delta is the only drill-seeded site and is a test site for very-early maturing varieties because it has cooler growing conditions than other rice growing regions of the state. Variety trial results will be available in the February 2025 newsletter.

Armyworm Monitoring: In 2024, we monitored for true armyworms on three Delta farms, and moth catches peaked around July 1st (Fig. 1). I observed that feeding damage was highly variable across the three farms but also across fields on the same farm. This has important implications for in-season management and highlights the importance of scouting for crop damage and the presence of worms. UC IPM guidelines provide monitoring guidelines and treatment thresholds. While a second peak has sometimes been observed in the Sacramento Valley, we have not observed a second peak after heading in the Delta.

Figure 1. Delta true armyworm trap counts, 2016-2024. Data represent the average moth catches across nine traps (three traps at three different farms).

Weedy Rice: We need to stay vigilant in our efforts to prevent the spread and manage weedy rice. Early in the season, weedy rice is often mistaken for watergrass because it grows taller than the cultivated rice. However, I have noticed that watergrass (and barnyardgrass) will head sooner than weedy rice, and weedy rice has a lime green color in full light. There is a video on the CA Weedy Rice website that can help with identification or call me if you would like help. In-season management includes rogueing or spot spraying before viable seed is produced. The organic herbicide Suppress is registered for spot spraying. Post-harvest management should include straw chopping, but not incorporation, and winter flooding. This will keep seed on the soil surface where it can potentially deteriorate over the winter. With my colleagues, Whitney Brim-DeForest and Luis Espino, I will host a meeting for the Delta rice industry in early 2025 to provide weedy rice research updates and management information. Stay tuned for the meeting announcement.

Cover Cropping: With funding from the CDFA Healthy Soils Program and CA Rice Research Board, we are evaluating whether cover cropping improves soil carbon and nitrogen dynamics in the rice system. We are also assessing cover crop species performance, like survivability and biomass production. Since rice may be grown over multiple seasons without rotation, cover crops may provide an opportunity to introduce plant diversity, including nitrogen-fixing legumes. While the 2022-23 winter season was excessively wet, which hindered cover crop establishment, the 2023-24 season started off dry, so sowing and establishment were successful. We observed that the brassicas emerged quickly and started covering the soil after just one month, but when rainfall became more frequent after the new year, the brassicas died off. In contrast, the two vetches and balansa clover started off slowly but had vigorous stands by early spring, despite the wet conditions. For more information on these trial results, please visit my blog article. The 2024-25 winter season will be our third and final year of trialing.

Disease Observations: In past years, I have been called out to fields to help diagnose diseases, which were later confirmed as stem rot, aggregate sheath spot, or rice blast. The 2024 season, however, was a relatively light disease year, and my colleague, Luis Espino, also observed that in the Sacramento Valley. Just to recap, it is important to scout for these diseases at late-tillering and early-heading because fungicide treatments are most effective when applied between late-boot and early-heading. Rice blast may be exacerbated by too much nitrogen, and stem rot and aggregate sheath spot by low potassium (K), so proper plant nutrition is a good strategy to mitigate disease. K can be limiting in some Delta soils, so one of my future goals is to do K fertilizer rate trialing to determine if it can reduce disease incidence and/or boost yields.

Herbicide Resistance Testing: UCCE, under the direction of Extension Specialist Kassim Al-Khatib, provides herbicide resistance testing for rice growers. If you suspect that weeds have developed resistance to certain herbicides, please collect mature weed seeds at the end of the season and submit them to me.

Alternate Wetting and Drying: Earlier this year, I applied for funding from the Delta Science Program to evaluate the practice of Alternate Wetting and Drying (AWD) in the Delta. AWD is a management practice where a flooded field is temporarily drained during the growing season and then re-flooded. Research from other states and countries has shown that the practice can reduce methane emissions from rice fields, but there has not been research done in the Delta, with its unique soil and climate conditions. If the grant is awarded, this project would begin during the 2025 season.

I want to take this opportunity to thank all the growers who collaborated with us on these projects. I wish everyone a happy, healthy end to 2024.

Results for the 2024 UCCE Delta field corn variety trial are now available. The trial took place on Tyler Island in Sacramento County. The trial was planted on April 26 and included nine varieties submitted by seed companies and two by the cooperating grower. We evaluate varieties across three replicate blocks for performance under Delta conditions, including high organic matter soils and pest pressures typical for the region. The trial was harvested on October 14.

A couple things stood out in 2024. There were periods of exceptionally hot weather during the season, including during bloom. Corn has photosynthetic adaptations that impart heat tolerance, but research has shown that the photosynthetic capacity of corn can be impeded when high leaf temperatures inactivate photosynthetic enzymes. High mid-season temperatures may have impacted yield for some varieties, but overall performance appears comparable to previous years. Also, Fusarium ear rot incidence was relatively high this year, and members of the industry have confirmed this for other regions of the state. Head smut incidence was low this year, and common smut is not widely observed at this site.

Six varieties yielded similarly well, based on statistical analysis, and varieties that yielded lower in the trial had a higher incidence of Fusarium ear rot. In addition to yield, there were also statistical differences in stand count, days to bloom, ear height, grain moisture, and bushel  weight. A table of results, as well as more information about the experimental design, data collection, and statistical analysis are available from the full report.

The Kearney Field Crops, Alfalfa and Forage Field Day will be on Friday, September 13, 2024. The field day will take place at the Kearney Research and Extension Center, 9240 S. Riverbend Ave., Parlier, CA 93648. Sign-in and morning refreshments begin at 7:00am, and the field tour tram leaves promptly at 8:00am. There is no registration fee, but please pre-register for the event to help us with our planning. Only pre-registered attendees are guaranteed a lunch. CCA (1.0 SW, 1.5 PM, 1.0 CM), CDFA INMP (1.0), and DPR (2.0 of Other) continuing education credits have been approved. The agenda is below and attached to the bottom of this post. We look forward to seeing you at the field day!

Agenda:

7:00 am     Sign-in (refreshments provided)

8:00 am     Depart for Field Tour

• Sorghum Variety Trials (Grain & Forage) – Jackie Atim, UC ANR
• Sorghum Variety Trial under Deficit Irrigation – Jackie Atim, UC ANR
• Deficit Irrigation in Alfalfa – Daniel Putnam, UC Davis
• Blackeye Bean Variety Selection – Bao Lam Huynh, UC Riverside
• Weed Identification – Giuliano Galdi, UC ANR
• Pesticide Spray Calibration and Equipment Demonstration – Jorge Angeles, UC ANR

10:30 am    Return from Field Tour

10:40 am    Regional Garbanzo Variety Trials – Michelle Leinfelder-Miles, UC ANR

11:00 am    New Safflower Insecticide Uses– Nick Clark, UC ANR

11:20 am    Break

11:30 am    New Data on Insecticide Resistance in Alfalfa Weevil – Ian Grettenberger, UC Davis

11:50 am    Wheat, Barley, and Triticale Deficit Irrigation Trials – Ranjit Riar, Fresno State

12:10 pm    Lunch