In 2021, rice acreage in the Delta, south of the Yolo Bypass, was roughly 6,600 acres. Most of the Delta acreage is in San Joaquin County, with a few hundred acres in Sacramento County. Delta rice acreage has been steadily increasing over the last several years (Table 1). Most of the acreage was planted with variety M-206, but I have heard that a small amount of M-105 was also planted.
Table 1. Rice acreage and yield according to the San Joaquin County Agricultural Commissioner's crop reports. County rice production is predominantly (if not entirely) in the Delta region. The 2021 acreage estimate includes a few hundred acres in the Sacramento County Delta.
Pest pressure was not especially high across the region in 2021, but I consulted with growers and consultants on a handful of pests. Watergrass, barnyardgrass, and sprangletop can be problematic weeds. These are generally controlled by a spray program applied by ground pre-flood, when the rice has 3-4 leaves. Windy conditions can compromise optimal timing for herbicide applications, and this year was no exception. Typically, a second application is not made, but some growers contemplated it this year for escaped grasses. Over the last two years, I have conducted trials to evaluate the efficacy of a new product, Loyant (florpyrauxifen-benzyl; Corteva Agriscience), on these grasses in the Delta drill-seeded system. This year, we evaluated product efficacy on nutsedge, and those results will be forthcoming.
I have been trapping armyworms in the Delta since 2016, and like in the Sacramento Valley, armyworm populations were very low this year. Some growers indicated needing to treat some of their acreage, particularly where rice was neighbored by riparian or wetland vegetation, but other growers did not treat. Annual trap counts for the Delta are available on my website.
Last year, we started observing stem rot (Sclerotium oryzae) on some farms but not until late in the season when the fields were drained. We developed post-harvest straw management programs, which appear to have mitigated the problem but not eliminated it. Next year, we will monitor for the disease early in the year, and a fungicide application may be necessary on some farms. There is a tendency for stem rot to be more severe on low potassium soils, and most Delta soils are naturally low in potassium.
For a few years, we have been monitoring some ranches where we have identified weedy rice. On one farm that had a light infestation, it appears that the grower has eliminated weedy rice with in-season rogueing, post-harvest management that included straw chopping but no incorporation, and winter flooding. These appear to be important practices, especially with light infestations, and in particular until a herbicide is approved for spot-spraying. We also advise that growers pay attention to equipment sanitation – harvesting weedy rice fields last (if possible) and thoroughly cleaning out equipment after harvesting fields with weedy rice.
Cooler temperatures in the Delta, compared to the Sacramento Valley, make the Delta a challenging place to grow rice. Growers are limited to using only very-early and early maturing varieties. In 2021, we revived the UCCE variety trial in the Delta location, which will help in the identification and advancement of cold-tolerant varieties. Low night time temperatures can cause blanking, which results in empty grains. We expect blanking to occur when the developing pollen grains are exposed to nighttime temperatures at or below 55 degrees F for several hours. I am aware of a late-planted ranch that may have experienced some blanking due to cooler temperatures at the time of panicle development, but blanking should not be a problem for the majority of fields that were planted by mid-April.
Overall, 2021 was a successful year for Delta rice growers. Thank you to all my colleagues in the industry, and especially to my trial cooperators.
In previous years, we trapped for both true armyworms and western yellowstriped armyworms. It appears, however, that the true armyworms are the ones that damage rice, so this year, we focused our trapping on them. I trap on three islands in the Delta, and I did see some leaf feeding damage in June. Moth flights peaked in late June (Fig. 1), but overall, damage was not severe this year. In fact, the moth counts were the lowest that I have seen since I started trapping in 2016. Some growers indicated needing to spray, but others did not. For those who sprayed, populations fell and did not resurge later in the season. I saw very little, if any, panicle injury in August and September.
You can find more information about my Delta rice research and extension program on my website. I wish you a successful harvest season!
Figure 1. Delta true armyworm trap counts. The trap counts represent the number of moths caught per day, averaged across three Delta locations. The 2021 counts were the lowest seen since trapping began in 2016.
UC Cooperative Extension has responded to the problem by providing outreach on UC IPM guidelines for monitoring and treatment. We have also cooperated with the California Rice Commission on getting Section 18 emergency approvals of methoxyfenozide (Intrepid 2F), which has been approved for the 2021 season. (For more information, please contact your county Agricultural Commissioner's office.)
In cooperation with Luis Espino, Rice Advisor in Butte and Glenn counties, I have been monitoring armyworm populations in Delta rice since 2016. Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the moths. As of the week of June 14th, trap catches in the Delta are still low – about two moths per day – but there is some variation across locations, with lower Roberts Island having higher catches than Wright-Elmwood Tract and Staten Island. Over the years, the peak trap catches have occurred from the middle of June to early July (Figure 1), so now is the time to ramp up monitoring.
In previous years, we have trapped for both true armyworms and western yellowstriped armyworms. It appears, however, that the true armyworms are the ones that damage rice, so this year, we have focused our trapping on them. There are three locations in the Delta, and at each location, there are three traps that span adjacent fields. Therefore, we're able to monitor population variation within locations and across locations.
Armyworm larvae can grow to full size in three to four weeks. Because small armyworms are hard to scout and large armyworms are hard to treat, we use trap counts and Growing Degree Day modelling (i.e. a temperature measure of time) to determine when the worms are “just right” to treat. (Pardon the Goldilocks reference!) During the season, Luis writes a weekly blog to provide real-time information on trap counts to help growers and consultants with scouting and decision-making. This year, he is also using an interactive mapping tool called Ag Pest Monitoring, which you can use to view counts in real-time and across trapping locations. Please consider subscribing to Luis Espino's blog.
Figure 1. 2016-2021 Delta armyworm trap counts. The trap counts represent the number of moths caught per day, averaged across three Delta locations. The 2021 counts are still low, averaging just two moths per day during the week June 14th, but now is the time to intensify monitoring since peak populations tend to occur between now and early July.
UC Cooperative Extension has responded to the problem by providing outreach on UC IPM guidelines for monitoring and treatment. We have also cooperated with the California Rice Commission on getting Section 18 emergency approvals of methoxyfenozide (Intrepid 2F), which has been approved for the 2020 season. (For more information, please see CA Rice News.) Research and extension efforts have been led by Luis Espino, Rice Advisor in Butte and Glenn counties. He has conducted product efficacy trials and initiated widespread monitoring in the Sacramento Valley. In cooperation with Luis, I have been monitoring populations in Delta rice.
Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch true armyworm and western yellowstriped armyworm moths (Figure 1). Because small armyworms are hard to scout and large armyworms are hard to treat, we use trap counts and Growing Degree Day modelling (i.e. a temperature measure of time) to determine when the worms are “just right” to treat, knowing that armyworm larvae can grow to full size in three to four weeks. During the season, Luis writes a weekly blog to provide real-time information on trap counts to help growers and consultants with scouting and decision-making. Please consider subscribing to the blog.
I have been monitoring populations in the Delta since 2016. This year, I deployed the traps about a week earlier than I have in past years. The traps are already catching moths (Figure 2), so it will be important to begin scouting for feeding damage. I will provide periodic monitoring updates using this blog, but for weekly updates, please consider subscribing to Luis Espino's blog.
Figure 2. 2016-2020 Delta armyworm trap counts. The trap counts represent counts of true armyworm and western yellowstriped armyworm moths. The counts are average across three San Joaquin County fields.
The 2017 season was marked by weather extremes, including record winter rainfall and high summer temperatures. Despite those, Delta rice growers generally observed an average to above-average season. Total acreage for the Delta south of the Yolo Bypass was roughly 2900 acres. For some growers, acreage was up because they were able to get ground preparation done early, but for others, acreage was down because the ground was late to dry out. Most of the Delta acreage is in San Joaquin County, with a few hundred acres in the “tail” of Sacramento County. The acreage was entirely drill-seeded, as is typical for the Delta, and planted with M.206.
Annual rainfall (October 1, 2016 to September 30, 2017) for the region varied greatly by location. CIMIS stations for the south Delta reported rainfall from 16 to 20 inches, but stations in the north Delta reported 28 to 38 inches. Most of this rainfall fell in October through January. Spring rainfall lingered into the month of April, but accumulation of at least a tenth of an inch ceased by mid-April. Given the high organic matter content of many Delta soils, fields generally dried out for on-schedule planting in late-April through early-May, with few exceptions.
Cooler temperatures in the Delta, compared to the Sacramento Valley, make the Delta a challenging place to grow rice. The summer of 2017, however, brought many days over 100⁰F. This varied greatly by location, with some areas in the north Delta having approximately 10 days over 100⁰F and areas of the south Delta having 25 days over 100⁰F, according to CIMIS stations. Hot days meant warmer nights, which was a good thing for Delta rice culture. Delta rice can experience blanking due to low night-time temperatures, influenced by Delta breezes. We expect blanking to occur when the developing pollen grains are exposed to night-time temperatures at or below 55⁰ F for several hours. Across four Delta CIMIS stations, the average minimum temperature from August 1st to September 15th was 60⁰F.
Harvest was generally on-schedule and occurred from late-September to early-October. Anecdotally, yields were up and averaged over 90 cwt/acre. Growers suspect that the higher summer temperatures (including higher night-time temperatures) resulted in less blanking and higher yields.
Overall, Delta rice growers had an average to above-average year as we close out 2017. Let's hope for a similar 2018.