UC Cooperative Extension will host a Weedy Rice Meeting on Thursday, March 31, 2022 from 10:00am to 11:30am. The meeting location is the Cabral Agricultural Center in Stockton (2101 E. Earhart Ave., Stockton, CA 95206). A printable version of the agenda is attached at the bottom of this post. The agenda is as follows:

10:00am  Weedy Rice Identification Refresher/Review, Luis Espino, Whitney Brim-DeForest, UCCE

10:15am  Current Status of Weedy Rice – Acreage Surveys, Luis Espino, Whitney Brim-DeForest, Michelle Leinfelder-Miles, UCCE

10:30am  Seed Certification Process/Rules and 2021 Observations, Timothy Blank, CA Crop Improvement Association

10:45am  Best Management Practices, Luis Espino, Whitney Brim-DeForest, Michelle Leinfelder-Miles, UCCE

11:00am  Research Updates, Whitney Brim-DeForest, UCCE

11:15am  Open Discussion – Q & A

We have submitted applications for continuing education, including credits for pesticide licensing (1.5 of Other) and certified crop advisers (1.5 of PM). Refreshments will be provided. If you require special accommodations, please contact UCCE San Joaquin County at 209-953-6100. Thank you, and hope to see you at the meeting!

Last year, we reinstituted the San Joaquin County Delta rice variety trial, after a four-year break. San Joaquin County is one of twelve locations of the statewide trial that evaluates commercial varieties and advanced breeding lines. San Joaquin County is a test site for very early maturing varieties because the Delta is cooler than other rice growing regions of the state. The trial was drill-seeded on April 16^th at a rate of 150 lb/acre and harvested on October 7^th.

Statewide results will be available from the UC Rice webpage (https://rice.ucanr.edu/Reports-Publications/Agronomy_Papers/). Table 1 (below) shows the San Joaquin County results. Among the entries, M-206 is the most commonly planted variety in the Delta, followed by M-105. The average yield across all commercial varieties and advanced lines was 10,129 lb/ac. When interpreting the results, the CV, or coefficient of variation, is a measure of variability in the data in relation to the mean. The LSD (.05), or least significant difference at 95%, is used to compare means of different varieties. When the difference between two varieties exceeds the LSD value, we are 95% certain that the two varieties performed differently; the results are not due to random chance.

This trial helps to support the Delta rice industry, which has a different production system from the Sacramento Valley. We plan to continue trialing rice varieties in the Delta again in 2022. Please don't hesitate to reach out if you have questions about Delta rice production, and good luck this season!

Table 1. 2021 San Joaquin County very early rice variety test (advanced lines and varieties).

From 2019-2021, we conducted trials to evaluate the efficacy of a new herbicide product called Loyant (florpyrauxifen-benzyl; group 4 herbicide; Corteva Agriscience) in Delta drill-seeded rice.  Loyant is registered in rice growing states in the southern US but would be a new chemistry in California. Previous work by the company indicates that Loyant provides good control of broadleaf weeds (e.g. ducksalad, redstems), smallflower umbrella sedge, and ricefield bulrush. Results from 2019 and 2020 Delta trials indicate that Loyant has efficacy on grass weeds in the drill-seeded system, like watergrass and barnyardgrass (Echinochloa spp.). The objective of the 2021 trial was to assess the efficacy of Loyant on yellow nutsedge (Cyperus esculentus) (Figure 1).

Figure 1. The most prevalent weeds in the 2019 and 2020 trials were A) watergrass and barnyard grass (Echinochloa spp.) and B) sprangletop (Leptochloa fusca). The most prevalent weed in the 2021 trial was C) yellow nutsedge (Cyperus esculentus).

Please see the full report for trial methods, including treatment list and rates, and complete results with discussion. In 2021, we observed minor crop injury with all treatments in the form of leaf tip burning, but symptoms were no longer visible two weeks after treatment. No other injury symptoms were observed. In terms of weed control, the best treatment for yellow nutsedge in this trial was the grower standard program, which contained Sandea. Several Loyant treatments performed statistically similar to the grower standard herbicide program and better than the Prowl (“control”) treatment (Table 1). Loyant alone performed statistically worse than the grower standard program in this trial. While Loyant is registered for yellow nutsedge in other states, lack of moisture can impact efficacy. The delay in establishing the permanent flood may have affected its efficacy in this trial. At 64 DAT, we observed that Echinochloa grasses had grown in the Prowl treatment, but they were controlled with the other treatments. The observations agree with the 2019 and 2020 trial results, where Loyant and Loyant tank mixes showed good efficacy on Echinochloa spp.  

Table 1. Percent weed control, as plot area, was estimated on 7-day intervals from 14 days after treatment (DAT) to 35 DAT. An untreated area of the field had approximately 1-4 sedges per square foot.

We also had a non-replicated demonstration site (on a different farm) where we evaluated post-flood applications of Loyant alone and in tank mixes. Treatments were applied in late-June, when grasses were heading, with the purpose of evaluating efficacy on grasses that had escaped the pre-flood grower standard program. No crop injury was observed with any treatments. Weed control was compared to a non-treated area outside of the demonstration area. All treatments had efficacy on grasses, but the Loyant/Clincher treatment appeared to work best under these circumstances.

Conclusions:

The purpose of the trial was to learn the crop tolerance and weed control efficacy of Loyant (florpyrauxifen-benzyl) in drill-seeded rice, with the specific objective in 2021 to evaluate efficacy on yellow nutsedge. The best treatment for yellow nutsedge control in this trial was the grower standard program. Loyant, alone, was not efficacious on yellow nutsedge, but performed well in tank mixes with other products. Three years of results trialing Loyant in the Delta drill-seeded system indicate that it could be used in herbicide programs, providing a different chemistry for herbicide resistance management.

The aforementioned information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.

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.

The season was influenced by the severely dry winter that preceded it. Delta rice is entirely drill-seeded (Figure 1). The fine, organic soils present challenges for water-seeding; namely, soil particles go into suspension and then bury the seed too deeply, resulting in poor germination. Growers who were planted by mid-April were generally able to plant to moisture. These growers were starting to harvest by late September and early October and beat the late-October rains.

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) 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.