- Author: Michelle Leinfelder-Miles
In 2022, I estimate rice acreage in the Delta, south of the Yolo Bypass, was at least 8,000 acres. Most Delta rice is grown in San Joaquin County, but there is some acreage in Sacramento County. While Delta rice acreage is relatively small compared to that in the Sacramento Valley, it has been steadily increasing over the last several years (Table 1).
Table 1. Rice acreage and yield according to the San Joaquin County Agricultural Commissioner's crop reports. County rice production is predominantly in the Delta region.
Given the increasing interest in rice production among Delta growers, and the differences in production practices from the Sacramento Valley, UC Cooperative Extension and UC Davis will be releasing a cost of production report specifically for Delta rice later this year or in early 2023. A Delta rice cost study was last produced in 2007, so updating the study was long-overdue. I want to thank all the growers who participated in a focus group to update the study.
Cool temperatures can make the Delta a challenging place to grow rice. Low night-time temperatures can cause blanking, which results in empty grains. Growers are limited to using only very-early and early maturing varieties. Most of the Delta acreage was planted with variety M-206, but some growers also planted a portion of their acreage with M-105. In 2022, we continued the UCCE Delta variety trial, which will help to identify and advance cold-tolerant varieties. The Delta trial is part of a statewide network of trials, led by UC Rice Extension Specialist, Bruce Linquist, and coordinated by Staff Researcher, Ray Stogsdill. I anticipate that the statewide results will be ready in early 2023.
This year, I worked with growers and consultants on a handful of pests. Weed management is always top-of-mind for rice growers. There are limited practices and products that can control problematic weeds, and in some circumstances, the weeds may develop resistance to the herbicides that are available. If herbicide resistance is suspected, please contact me so that we can submit weed seeds for testing. We would collect the seeds in the late summer or early fall when they have matured but have not shattered. Resistance testing is overseen by UC Weed Science Extension Specialist, Kassim Al-Khatib, and takes place in greenhouses during the winter. By the following spring, we provide the grower with information on which herbicides are still working and which are not.
I have been trapping armyworms in the Delta since 2016, in collaboration with fellow farm advisor, Luis Espino. The traps catch true armyworm moths. They were deployed on three ranches and monitored weekly. In 2022, we recovered the highest moth counts since 2017, and the peak flight occurred about one week earlier than in 2017. This is important information for management because, based on the armyworm life cycle, we know that peak worm populations occur approximately two weeks after peak moth flight. In other words, growers can make informed decisions based on the monitoring data and adapt their management to the field conditions. Trap monitoring is one part of an integrated pest management program for armyworms, which also includes scouting for feeding damage and the worms themselves. Over the years, I have observed armyworms in riparian and wetland vegetation that neighbor rice fields, so it is important to scout those areas, too.
We should continue to keep weedy rice on our radars because we have seen it in the Delta in the past. Where we have observed light infestations, it appears that keen management – including in-season rogueing, post-harvest management that includes straw chopping but not incorporation, and winter flooding – can reduce, if not eliminate the pest. These are our management tools until a herbicide is approved for spot-spraying. Growers should also pay attention to equipment sanitation – harvesting weedy rice fields last (if possible) and thoroughly cleaning out equipment after harvesting fields where weedy rice has been observed.
Finally, I will be starting new projects this winter, in collaboration with fellow farm advisor, Whitney Brim-DeForest, and graduate student, Sara Rosenberg, to evaluate winter cover cropping between rice crops. Our objectives are to evaluate carbon and nitrogen cycling and variety survivability during the cool, wet (we hope!) winter conditions. These projects are supported by the CDFA Healthy Soils Program and the CA Rice Research Board. I look forward to sharing results in the years to come.
I am grateful to work with a great team of UC colleagues on these rice projects. I am also grateful for all the growers who have collaborated with us. I wish everyone a good end to the year, and I look forward to working with you again in 2023.
- Author: Michelle Leinfelder-Miles
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.
- Author: Michelle Leinfelder-Miles
Weeds are important pests of California rice systems, and weed management can account for roughly 17 percent of total operating costs, according to a UC cost of production study. Integrated weed management uses cultural and chemical practices and considers the following:
- Prevention (e.g. using certified seed, equipment sanitation, maintaining roads and levees)
- Cultural practices (e.g. land leveling, crop rotation, tillage, winter flooding, drill-seeding)
- Fertilizer placement and management
- Water management
- Monitoring
- Herbicides
Herbicides are important tools; however, resistance can occur when products are not rotated, or when diverse chemistries are not available.
In 2019, in cooperation with Corteva Agriscience, I conducted a trial to evaluate the efficacy of a new herbicide product called Loyant (florpyrauxifen-benzyl). Loyant is registered in rice growing states in the southern US but would be a new chemistry in California. Corteva Agriscience anticipates California rice registration in 2020, with the product being available for use in 2021. Previous trials have shown that Loyant provides good control of broadleaf weeds (e.g. ducksalad, redstems), smallflower umbrella sedge, and ricefield bulrush. It has some activity on Echinochloa species (e.g. barnyardgrass, watergrass). More data was needed, however, in drill-seeded systems. The objective of the trial was to assess the efficacy and crop tolerance of Loyant for weed control in drill-seeded rice in California.
The trial took place in the Delta region on a Kingile muck soil. This soil classification is characterized as having upwards of 40 percent organic matter in the top foot of soil. On high organic matter soils in the Delta, the typical practice is drill-seeding. Water-seeding, which is the typical practice in the Sacramento Valley, is not successful in the Delta because the soil particles can float and move too easily, causing seed to get buried too deeply and germinate poorly.
For a full report on this trial with methods and crop injury data tables, please see my website. Treatments are described in Table 1 below. We observed slight to noticeable leaf curling in the Loyant treatments at 14 days after treatment (DAT), but this had disappeared by 21 DAT. We observed no stunting or stand reduction with any of the treatments; nor did we observe any differences in heading. All treatments had similar weed control with the exception of the Prowl-only treatment, which had statistically higher weed counts. Loyant does not control sprangletop, so sprangletop was the weed most commonly observed. We found no differences in yield or seed moisture at harvest (Table 2 below), and we observed no lodging. Yield averaged 8965 pounds per acre across treatments, and seed moisture averaged 13.7 percent.
In summary, the purpose of this trial was to learn the efficacy and crop tolerance of Loyant (florpyrauxifen-benzyl) for weed control in drill-seeded rice. We observed slight leaf rolling with the Loyant treatments a couple weeks after treatment, but those symptoms were gone by the third week after treatment. We observed Loyant to have good activity on the Echinochloa species but not on sprangletop, which was expected based on previous company trials. We observed Loyant treatments to have similarly low weed counts compared to the grower standard practice, and no significant differences in yield among the treatments. Tank mixes will be needed to manage sprangletop. The results indicate that Loyant could be used in drill-seeded rice herbicide programs, providing a different chemistry for herbicide resistance management.
This information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.
Table 1. Rice herbicide treatments.
- Author: Michelle Leinfelder-Miles
To say it has been a strange year would be par for the course. When don't we have a strange year anymore?! To say it has been a wet year, however, would be an understatement. According to the National Oceanic and Atmospheric Association, normal rainfall for the “water year” (October 1st through September 30th) is 14.06 inches for Stockton, CA. Last winter, we received 15.29 inches in Stockton from October 1st to April 11th. This year, we have received 20.75 inches to date.
With the high rainfall, we have received many inquiries about how to manage poor stands of alfalfa. Dan Putnam, UC Alfalfa and Forage Specialist, anticipated these sorts of problems early in the year and posted this article to the Alfalfa and Forage News blog. With this posting, I follow up with a Q&A of things I've heard and discussions I've had since that article was written. Remember that every situation has its unique set of conditions, and recommendations should be site specific.
1. There are poisonous weeds (e.g. groundsel, fiddleneck) in spots of the fields where the stand is poor. The weeds are not widespread, but they are no longer seedlings. What can be sprayed on these weeds?
Rachael Long, farm advisor in Yolo, Solano, and Sacramento counties, described these weeds and some treatment options in a recent article. In this particular example, where the weeds are not widespread and probably too big for effective herbicide treatment, an option could be to cut those portions of the field and get rid of that weed-infested hay. The rest of the field could be cut and baled as usual. Once groundsel and fiddleneck have been cut, they will have a hard time competing with the alfalfa plants in subsequent regrowth and cuttings.
2. A grower generally cuts a field for the first time around the first week of April. The stand was still pretty short at that time. If the grower stayed on his typical schedule, would cutting when the alfalfa is short stimulate growth, or would it be better to wait to cut?
If the field has poisonous weeds, as described in Question 1, an early cutting might be appropriate, especially if the weeds are widespread in the field. The grower could cut early to manage the weeds, and since the hay is short, the grower would not lose a lot of yield. If the stand is clean of weeds, however, it would probably be advisable to put off the first cutting. Letting the plants grow, and perhaps go to an early stage of flowering, would help the root system develop and strengthen the plants.
3. Many growers and consultants have heard that alfalfa produces autotoxins, which cause poor establishment of overseeded alfalfa. How long do the autotoxins remain in the soil?
Autotoxicity is the effect of a chemical compound released by plants of the same species. The autotoxic effect can last in the field as long as there are decomposing crowns. Once the plant material has decomposed, the autotoxic effect doesn't usually last. Remember that there is also general competition between older/bigger alfalfa plants and young seedlings. This is not related to autotoxicity, but rather to the fact that seedlings are small and weak compared to the strong, multi-stemmed crown of a mature alfalfa plant.
4. Does overseeding alfalfa ever work?
I previously wrote an article on overseeding older alfalfa stands, and Dan Putnam wrote this article on this topic. Growers may overseed older alfalfa stands with grasses or legumes to prolong stand life, but of course, this year has presented extraordinary conditions where growers are considering what to do with poor stands that are of varying ages – even seedling fields planted last fall! Generally, we wouldn't recommend overseeding unless the current stand has less than 6-10 plants/ft2. In a situation where that was the case, both Dan and Mick Canevari, emeritus farm advisor in San Joaquin County, have seen poor stands of seedling alfalfa be successfully overseeded under certain conditions, namely, the seed was drilled into the previous stand and was planted to moisture. Additionally, having the option of sprinkling up the newly-planted seed can help in successful establishment. Remember that overseeding can sometimes lead to complicated weed management. Consider your weed management program (for the old part of the stand and the newly-planted part of the stand) before going to the effort and expense of overseeding.
5. A grower applied a herbicide in December with a 12 month plant-back, according to the label. Now, with all the rain, the stand looks really poor, and the grower wants to take out the alfalfa and plant something else. What should the grower plant?
Remember, the label is the law. If the label says there is a 12 month plant-back, then what that means is that there could be phytotoxic effects to a subsequent crop that is planted within 12 months. Sometimes, however, the label may specify shorter duration plant-backs for certain crops. Be sure to read the label carefully.
6. For fields that have had a history of problems with stem nematodes, is a poor stand from all the rain or from stem nematodes?
Unfortunately, this is probably a collision of both problems, and neither has a great solution. For reasons previously described, there are not a lot of solutions for poor stands resulting from saturated conditions. Likewise, there are not a lot of solutions for fields having stem nematode, regardless of whether the soil is saturated or not. Stem nematodes cause most of their problems when soils are cool and moist. We notice their impact in the spring when regrowth is poor, as with shortened internodes and possibly white flagging of stems. Once conditions have warmed, stem nematodes recede deeper into the soil and tend to not be a problem later in the year. The ways we can deal with stem nematode are limited but include planting highly-resistant (HR) varieties and having good equipment sanitation between infected and non-infected fields.
7. A grower has an alfalfa field where a portion of the field is in very poor shape, but the rest of the field looks ok. What could this grower do?
Dan Putnam and I recently visited a field in the Delta where this was the case. In fact, it was the higher end of the field where the stand was basically decimated, but over the winter, there was pretty pervasive standing water in much of the Delta. In this particular situation, the grower produces the alfalfa for his own dairy and can manage the field selectively. The grower will probably disc up the end of the field where the stand is bad and plant sudan there. He'll bale the sudan and then plant alfalfa there in the fall. This option seemed amenable to the grower, but of course, every grower is going to have a different set of costs, buyers, and circumstances.
There is no “one size fits all” on these questions. Every situation will have a slightly different recommendation depending on the conditions. Even as the spring turns to summer, we may still see alfalfa fields dying back as a result of the wet winter we've had. Keep the questions coming, but let's hope we can move forward into a productive spring and summer!