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.
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.
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
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.