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). (Photos A and C by M. Leinfelder-Miles. Photo B courtesy UC IPM)

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 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.

I have been trapping armyworms in Delta rice since 2016, in collaboration with my colleague in the Sacramento Valley, Luis Espino. Monitoring involves scouting for worm damage – like leaf feeding or panicle injury – and deployment of pheromone bucket traps that catch the moths. The worms are often difficult to find unless you are scouting early in the morning before it gets too hot, which is why we use the pheromone bucket traps. We can observe when moth populations are reaching their peak to inform treatment decisions. Over the years, UCCE has cooperated with the California Rice Commission to get Section 18 emergency approvals of methoxyfenozide (Intrepid 2F), and because we have trapping data from the Delta, San Joaquin County has been included on the approval. Thank you to the cooperating growers for allowing me to trap on their farms.

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.

I am pleased to announce the following meetings and webinars.

1. The Rice Experiment Station (RES) Annual Field Day will takes place next Wednesday, August 25, 2021 from 7:30am to 12:00pm, followed by lunch. The RES is located at 955 Butte City Highway (Hwy. 162), approximately two and one half miles west of Highway 99, north of Biggs, California. The field day is an opportunity to learn about the research being done at the RES, including variety development. It is sponsored by the California Cooperative Rice Research Foundation (CCRRF) and University of California (UC). For more information, please visit the RES website. 

2. Farmers' Rice Cooperative and Wetlands Preservation Foundation will host a Delta Rice Field Day next Thursday, August 26, 2021 from 8:30am to 1:45pm. The event will start at Canal Ranch (23011 Blossom Road, Thornton, CA 95686), followed by a bus tour of nearby Delta rice production. I will be present to answer questions about my rice research and extension program, including the Delta variety trial, armyworm monitoring, herbicide trials, and weedy rice outreach. Space is limited, so please see this flyer to reserve space.

3. The UC Dry Bean Field Day will take place on Tuesday, August 31, 2021 from 9:00am to 11:30am. The field day will begin at Honey Bee Haven, Bee Biology Road, on the UC Davis campus. Due to Covid-19 safety precautions, preregistration for this event is required. There is no registration fee. I invite you to view the agenda and register here. CCA continuing education credits (2.0) are available (0.5 of NM; 0.5 of PM; 1.0 of CM).

4. The UC Alfalfa and Forage Field Day will take place on Thursday, September 23, 2021 from 8:00am to 12:15pm, followed by lunch. The field day will take place at the Kearney Research and Extension Center, 9240 S. Riverbend Ave., Parlier, CA 93648. Due to Covid-19 safety precautions, preregistration for this event is required. There is no registration fee. I invite you to view the agenda and register here. We have applied for DPR, CCA, and N management (ILRP program) continuing education credits.

5. The Vertebrate Pest Council is hosting vertebrate pest webinars on September 28 (field rodents), September 29 (use of rodenticides), and September 30 (managing commensal rodents). The webinars run from 8:00am to 10:00am each day, and registration is required. Please see this flyer for more information.

Finally, the Covid-19 pandemic is a fluid situation. At this time, I plan to hold an in-person field meeting at the Delta field corn variety trial, as I have done in the past. The date is TBD but will take place in late-September or early-October. I will send a separate blog announcement when the date has been set. 

Thank you for your interest in our programs. Stay healthy, and hope to see you soon at one of these events.