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.
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.
Weeds are important pests of California rice systems, and weed management can account for roughly 17 percent of total operating costs (Espino et al., 2016). Integrated weed management uses cultural and chemical practices where herbicide are important tools. Certain conditions in California rice production systems, however, increase the likelihood of developing herbicide resistance. Herbicide resistance is the ability of certain weed biotypes to survive certain herbicide treatments when the weed species is usually killed by that herbicide (Al-Khatib et al., 2019). Such conditions include, but are not limited to, lack of crop rotation, the efficacy of certain herbicides on certain weeds causing them to get frequently used, and not having diverse chemistries available.
In 2019 and 2020, trials were conducted to evaluate the efficacy of a new herbicide product called Loyant (florpyrauxifen-benzyl; group 4 herbicide; Corteva Agriscience) in drill-seeded rice in the Delta region. Loyant is registered in rice growing states in the southern US but would be a new chemistry in California. Corteva Agriscience expects to have CA registration in time for the 2021 use season. The objective of the trials, by assessing different rates and treatment combinations, was to understand the efficacy and crop tolerance of Loyant for weed control in drill-seeded rice in California. This article will describe select results of the 2020 trial. Treatments are listed in Table 1 below. Complete information from both years is available from my website.
Crop injury. We made crop injury observations and weed counts on 7-day intervals for about two months following treatment. We observed tip burning in several of the treatments, but the symptoms were no longer apparent by 21 days after treatment (DAT). We observed leaf curling in the Loyant treatments until about 56 DAT. Corteva Agriscience has observed this symptom with Loyant in other trials where environmental stressors impact crop health, such as extreme cold or heat, drought, or poor fertility. We observed this symptom on the side of the plots closest to the field edge. We observed no stunting, stand reduction, or differences in heading with any treatments.
Weed control. Overall weed pressure was relatively low, observing about 1 weed per square foot in an untreated strip next to the trial. The prominent weeds in the field were Echinochloa species (i.e. watergrass, barnyardgrass; Figure 1, below). We did not have a completely untreated control but instead considered the pre-emergent only treatment (i.e. Prowl) the control. There was a trend for the Prowl treatment to have the highest weed counts. The treatments that had the best weed control were the grower standard and Loyant/SuperWham herbicide programs (Table 2, below).
Yield. We found no differences in yield, but there was a trend for the grower standard and the Loyant/SuperWham herbicide programs to have slightly higher yields (Table 3, below). Measured yields were uncharacteristically high for the region. Our explanation of the data is that we did our hand harvest in the early morning hours when there was a heavy dew. Because variability across the replicates was low, as indicated by the coefficient of variation, we believe the data demonstrate relative comparability of herbicide programs, even though the absolute values are high.
Conclusions. The purpose of the trial was to learn the efficacy and crop tolerance of Loyant (florpyrauxifen-benzyl) for weed control in California drill-seeded rice. We observed Loyant to have good activity on watergrass and barnyardgrass, which were the predominant weeds in the trial. We observed Loyant treatments to have similarly low weed counts compared to the grower standard, and a Loyant/SuperWham herbicide program appears to provide comparable weed control to the grower standard. The results demonstrate that Loyant could be used in drill-seeded rice 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.
Table 1. Herbicide treatments in the 2020 trial. Treatments were applied on May 8th, when the rice was approximately at the 3rd leaf stage.
Figure 1. Predominant weeds in the trial were watergrass and barnyardgrass.
Table 2. Weed counts on 7-day intervals from 14 DAT to 42 DAT. Data represent total number of weeds in the 400-ft2 plot and are the means across four replicates.
Table 3. Yield adjusted to 14 percent moisture. The trial was hand-harvested on Sept. 29, measuring one 10.8-ft2 (1-m2) quadrat per plot. The grower reported that harvest moisture was around 18.5 percent.
UCANR California Rice Virtual Field Day
When: August 26, 2020, 1:00-3:00 PM
Where: Online Zoom Webinar
Host: Whitney Brim DeForest, UC ANR County Director, Sutter-Yuba Counties and CE Rice and Wild Rice Advisor
Objectives/goals: The UC Cooperative Extension and California Rice Research Station will update attendees in the areas of variety development, disease and arthropod management, weed control, weedy rice, and fertility.
The full agenda can be viewed here.
Who should attend: California rice growers, Pest Control Advisers, and others interested in California rice production systems.
Continuing education units: Applied for 1 CEU from the California Department of Pesticide Regulation (DPR) and applied for 1 CEU from Certified Crop Adviser (CCA)
- Russell Rasmussen, Associate Director, California Rice Experiment Station, California Cooperative Rice Research Foundation
- Bruce Linquist, CE Specialist, Dept. of Plant Sciences, UC Davis
- Kassim Al-Khatib, CE Specialist, Dept. of Plant Sciences, UC Davis
- Whitney Brim-DeForest, CE Rice and Wild Rice Advisor & County Director, Sutter-Yuba Counties
- Luis Espino, CE Rice Farming Systems Advisor & County Director, Butte County
- Ian Grettenberger, CE Assistant Specialist, Dept. of Entomology, UC Davis
- Michelle Leinfelder-Miles, CE Farm Advisor, San Joaquin County
Contacts for more information:
- Logistics and registration: Rachel Palmer, ANR Program Support Unit, (530) 750-1361
- Course content:Whitney Brim-DeForest, UC ANR County Director, Sutter-Yuba Counties and CE Rice and Wild Rice Advisor
This field day is open to the public. Please share broadly to those who may be interested in attending.
THIS EVENT WILL BE RECORDED FOR EDUCATIONAL OR PROMOTIONAL USE BY THE UNIVERSITY OF CALIFORNIA. CONTACT THE ORGANIZERS OF THIS EVENT FOR MORE INFORMATION.