- Author: Whitney Brim-DeForest
- Author: Taiyu Guan
- Author: Troy Clark
- Posted by: Gale Perez
From the CAPCA Adviser magazine :: June 2022
Whitney Brim-DeForest is a UCCE Rice and Wild Rice Advisor for Sutter, Yuba, Sacramento, and Placer Counties; Taiyu Guan is an Assistant Specialist in UCCE Sutter-Yuba Counties; Troy Clark is a Rice Junior Specialist for UCCE Butte County.
Introduction
In California rice, herbicide resistance has been documented in Echinochloa spp. since the early 2000's. Recent reports of uncontrolled grasses, as well as possible new species or biotypes have precipitated renewed research on this genus. Sixty-four watergrass samples were collected from a survey conducted in 2020, with grower and PCA-submitted samples from across the Sacramento Valley, as well as samples collected from University of California and Rice Experiment Station fields. Those samples were representative of all the watergrass species/biotypes: late watergrass, junglerice, barnyardgrass, and the new biotype/species. This experiment was a follow-up to our 2018 screening of watergrass (CAPCA Adviser, 2021).
The overall objective of this study was to determine the distribution and status of resistance to currently-registered herbicides in these species (cyhalofop, propanil, bispyribac-sodium, penoxsulam, benzobicyclon+halosulfuron, clomazone, and thiobencarb).
Methods
In August and September of 2020, 64 watergrass samples were collected from rice fields across the rice-growing region of California (Figure 1). The samples were representative of the Echinochloa spp. present in California rice, but were likely resistant, as they were self-reported by growers and PCAs: late watergrass (Echinochloa phyllopogon), junglerice (E. colona), barnyardgrass (E. crus-galli), and a currently unknown new biotype which is being characterized in a complementary study (Table 1). The overall objective was to determine the distribution and status of resistance to currently-registered herbicides in these species (cyhalofop, propanil, bispyribac-sodium, penoxsulam, benzobicyclon+halosulfuron, clomazone, and thiobencarb). Two known susceptible controls of late watergrass (E. phyllopogon) were added to the screenings as controls.
Screenings took place at the Rice Experiment Station greenhouse in Biggs, CA, in the summer and fall of 2021. All formulations were tested at the 1.5 leaf stage of watergrass. Dormancy was broken for the watergrass by wet-chilling in the fridge for approximately two weeks before planting. Seeds were pre-germinated in the incubator. Pots were seeded and then thinned down to 4 plants per pot.
All foliar-applied formulations (cyhalofop, propanil, and bispyribac-sodium) were applied with the label-recommended surfactants. Applications for into-the-water herbicides (granular formulations of penoxsulam, benzobicyclon+halosulfuron, clomazone, and thiobencarb) were made onto the water surface of bins that were flooded to 10 cm above the soil surface of the pots (where the watergrass was planted). All liquid herbicide treatments were applied with a cabinet track sprayer with an 8001-EVS nozzle delivering 40 gallons of spray solution per acre (at a pressure of approximately 20 psi). A flood was applied at 10 cm above the soil surface 48 hrs after the foliar applications. All herbicides were applied at standard field rates for California rice, though not at the maximum label rate for all herbicides (Table 2).
At 14 days after treatment, the number of living plants per pot was counted, and fresh biomass was measured (per pot) by cutting plants at the soil surface and taking the weight (per pot). Dry biomass was measured after drying the fresh weight samples down to a constant weight. Samples were classified as resistant to an herbicide if the average percent (%) dry weight control was less than that of the susceptible controls.
Results
Out of the barnyardgrass samples (31), 23 were resistant to cyhalofop (CY), 3 were resistant to propanil (PR), and 26 were resistant to bispyribac-sodium (BS). Out of the late watergrass samples (9), there were 9 CY-resistant, 5 PR-resistant, and 9 BS-resistant. For the new unknown biotype samples (22), there were 17 CY-resistant, 3 PR-resistant, and 20 BS-resistant. For the granular formulations, barnyardgrass (31 samples) had 27 that were thiobencarb resistant (TH), 24 that were benzobicyclon+halosulfuron resistant (BH), 17 that were clomazone resistant (CL), and 26 that were penoxsulam resistant (PE). Out of the late watergrass samples (9), 9 were TH-resistant, 9 were BH-resistant, 6 were CL-resistant, and 9 were PE-resistant. For the new unknown biotype samples (22), there were 20 TH-resistant, 18 BH-resistant, 11 CL-resistant, and 20 PE-resistant.
The majority of the samples of all species are resistant to all of the tested herbicides, with only propanil and clomazone showing control of approximately 50% (or more) of the samples (Tables 3 and 4). Late watergrass is widely resistant to all of the herbicides tested, with only propanil showing some degree of control in roughly 50% of the samples. Surprisingly, 100% of samples tested were resistant to thiobencarb, benzobicyclon+halosulfuron, cyhalofop, bispyribac-sodium, and penoxsulam.
The new biotype is best controlled with clomazone (50% of samples) or propanil (76% of samples), while a smaller proportion of samples were controlled by the other herbicides tested. Barnyardgrass is best controlled by propanil (90% of samples), and clomazone (45% of samples).
Although the new biotype shows widespread resistance, its impact on yields is likely explained by more than just herbicide resistance and is likely due to its competitive ability as well.
Conclusions
The implications of this study reflect anecdotal evidence relayed by growers. Echinochloa spp. are becoming increasingly difficult to manage using our currently registered herbicides. For growers, this means it is increasingly difficult to plan an effective program that both controls grasses and prevents further selection for resistance. Aside from rotations with the above-utilized herbicides, some other alternative management strategies include: deep water, utilizing a stale seedbed, and rotating to a dry-seeded or drill-seeded system.
Deep Water:
Maintaining a deep flood (of at least 4–6 inches) can suppress some grass emergence. Deeper water will provide more suppression. Deep water also improves herbicide efficacy for granular herbicide applications, and the deep water may also improve efficacy of pre-emergent herbicides. Keeping the water on the field as long as possible will improve control. Watergrass typically emerges in the first 30 days after water is put on the field, so longer flood duration is better.
Stale Seedbed:
A stale seedbed has been shown to provide good control of watergrass in heavily infested fields. To implement a stale seedbed, prepare the field as normal (in spring). The field can be tilled or untilled. If untilled, please keep in mind that watergrass seeds typically only emerge from the top 6 cm (3–4 inches) of soil.
Once the seedbed is prepared, flood the field until water is 3 to 4 inches deep, then turn off water and let it sink into the soil. This will increase watergrass germination. Roughly 1 to 2 weeks later, spray a nonselective herbicide (make sure the field is fully drained to ensure coverage). Tillage can also be utilized in place of an herbicide, but avoid deep tillage, as it will bring up additional grass seeds. Timing of the herbicide application or tillage will depend on temperature. Warmer temperatures cause faster emergence of grass. Two weeks should be more than enough time to bring up most of the grass population that will be germinable (able-to-germinate), regardless of temperature.
If not planting rice, this process (flushing/flooding, followed by tillage or herbicide application) can be repeated multiple times throughout the season. If planting rice, flood up the field after the application of the nonselective herbicide (follow label for instructions on flood timing).
Rotation to Drill- or Dry-Seeded System:
Drill-seeding or dry-seeding rice allows for the use of pendimethalin, which is a different mode of action from all other currently-registered rice herbicides. Depending on the actual product used, pendimethalin may be best used in a drill-seeded system, due to the possible injury to emerging rice plants. Or it can be used in a dry-seeded system, where seed is flown on instead of drilled. For more information on application methodology, refer to the product herbicide label.
Original source: CAPCA Adviser magazine :: June 2022
- Author: Whitney Brim-DeForest
- Posted by: Gale Perez
Whitney Brim-DeForest is the UC Cooperative Extension County Director for Sutter and Yuba counties and the Rice and Wild Rice Advisor for Sutter, Yuba, Capitol Corridor MCP, Placer, and Nevada counties.
In 2020, we conducted a larger survey, with grower and PCA-submitted samples from across the Sacramento Valley (Figure 1), as well as samples we collected from UC and Rice Experiment Station fields. We had a total of 64 samples, which were representative of all of the watergrass species/biotypes: late watergrass, junglerice, barnyardgrass, and the new biotype/species.
I did a preliminary identification of the samples (Table 1), but better identification of the samples is currently in progress with the UC Davis Herbarium. From the preliminary identification, the new biotype/species were 34.4% of the samples, junglerice were 3.1% of the samples, barnyardgrass were 48.4% samples, and late watergrass were 14.1% of the samples. Junglerice, although not a current rice field weed, is found around the edges of rice fields, so it was included in the analysis. A representative photo of the panicles of the three major types is below (Figure 2).
Methods
The 64 samples collected in 2020 were the same samples used in the phenotypic analysis of weedy rice. The herbicides used for screening were: clomazone (Cerano®), thiobencarb (Bolero®), cyhalofop (Clincher®), benzobicyclon+halosulfuron (Butte®), penoxsulam (Granite GR®), bispyribac-sodium (Regiment®), and propanil (Stam® or SuperWham®). Rates were the recommended label rate (Table 2) with at least 4 replications per herbicide-sample combination.
Screenings took place at the Rice Experiment Station greenhouse in Biggs, CA, starting in the summer of 2021. The foliar applications and granular applications were conducted at different timings, and each was replicated twice in time. There were 3 replications of each treatment per sample. All formulations were tested at the 1.5-2 leaf stage of the watergrass. Dormancy was broken for the watergrass by wet-chilling in the fridge for approximately two weeks before planting. Pots were seeded and then thinned down to 5 plants per pot. All liquid formulations (Clincher®, SuperWham®, and Regiment®) were applied with the label-recommended surfactant (crop oil, crop oil, and Dyneamic®). Applications for into the water herbicides were made onto the water surface of bins that were flooded to 4” above the soil surface of the pots (where the watergrass was planted). All herbicide treatments were applied with a cabinet track sprayer with an 8001-EVS nozzle delivering 40 gallons of spray solution per acre (at a pressure of approximately 20 psi). At 7 days after treatment, plants were evaluated for visual percent control (in comparison to an untreated control). At 14 days after treatment, the number of living plants per pot was counted, and fresh biomass was measured (per pot) by cutting plants at the soil surface and taking the weight (per pot). Dry biomass was measured after drying the fresh weight samples down to a constant weight.
Results
On average, control of samples with granular herbicides was low (Figure 3). Junglerice, which is not a rice weed, but rather a weed that borders rice fields, was well controlled with Bolero® and Cerano®. It was not quite as well controlled with Butte® or Granite GR®. It was well-controlled by Clincher®, Propanil, and Regiment® as well (Figure 4). The two susceptible late watergrass samples were mostly well-controlled by Bolero® and Cerano® (Figure 3). They were not quite as well controlled with Butte® or Granite GR®. They were well-controlled by Clincher®, propanil, and Regiment® as well (Figure 4).
For the unknown samples, on average, control was poor with Bolero®, Butte®, and Granite GR®, regardless of species. Control with Cerano® was similar to control of the susceptible samples (Figure 3). We saw good control of all of the resistant samples with Clincher®, except for late watergrass. Propanil showed good control of all species as well. Regiment® had poor control of all of the species, except for junglerice (Figure 4).
Conclusion
To all growers and PCA's that submitted samples, we will be sending individual screening results, as there are differences between the samples in terms of resistance to different herbicides.
For growers, the implications of this preliminary screening are that control of this new biotype/species will need to be prioritized early in the season. Possible treatments (keep in mind that these have not been field-tested and could cause phytotoxicity) could be: a stale seedbed using a non-selective herbicide; pre-plant Abolish® (thiobencarb) followed by Cerano® or Butte® or Granite GR®; Cerano® followed by Butte® or Bolero® or Granite GR®; or Butte® followed by Granite GR® or Bolero®. There is still a strong likelihood that a follow-up application may still be required later in the season, even with these early-season applications.
Original source :: Rice Notes - Feb. 2022
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- Author: Whitney Brim-DeForest
Watergrass
We are having more and more difficulties controlling watergrass over the past 20 or so years. We know that as of the early 2000s, we had found multiple-herbicide resistant late watergrass (also known as mimic), as well as multiple-herbicide resistant barnyardgrass. For early watergrass, we now have resistant biotypes (to thiobencarb), with none recorded as being multiple-herbicide resistant.
In 2017, two rice fields were identified with an unknown watergrass biotype (or species) that looked very different than the three main known species that infest California rice fields (late watergrass, early watergrass, and barnyardgrass). Both fields had extensive infestations, which were uncontrolled by repeated herbicide applications. The lack of control was coupled with outward characteristics that were not immediately identifiable to one of the known species. After extensive attempts at identification at both the UC Davis Herbarium, and even with the assistance of two Echinochloa experts at two other universities, we were unable to conclusively identify the species. In 2018, 10 more fields were identified, and samples were collected and screened for herbicide susceptibility in 2020. Rates are below (Table 1).
Trade Name | Active Ingredient | Rate |
Cerano® | clomazone | 12 lb a-1 |
Bolero® | thiobencarb | 23.3 lb a-1 |
Butte® | benzobicyclon + halosulfuron | 7.5 lb a-1 |
Granite GR® | penoxsulam | 15 lb a-1 |
Clincher® | cyhalofop | 15 fl oz a-1 |
Regiment® | bispyribac-sodium | 0.57 oz a-1 |
SuperWham® | propanil | 6 qt a-1 |
Results
10 of the 10 unknown watergrass samples were not controlled at 14 Days After Treatment (DAT) (less than 50% by biomass, in comparison to the untreated controls) by Granite GR® or Butte® (Table 2). 9 of the 10 samples were not controlled by Bolero®, and 6 of the 10 were not controlled by Cerano®. SuperWham®, Regiment®, and Clincher® controlled 10 of 10 samples (at least 50% control).
For the number of living plants remaining at 14 DAT, 10 of the 10 unknown watergrass samples were not controlled by Granite GR®, Butte®, Bolero®, or Cerano® (50% or more of the plants remained) (Table 3). 10 of the 10 samples were not controlled by Regiment®, 9 of 10 were not controlled by Clincher®. SuperWham® controlled 10 of 10 samples (at least 50% control).
Conclusion
The results of this screening closely align with what growers are seeing in the field: the unidentified watergrass is escaping early-season granular control and is then difficult or impossible to control with late-season herbicide applications. Foliar applications in the greenhouse were highly effective (by percent biomass reduction), but since the greenhouse application was conducted at an early timing (1.5 leaf stage of grass), it is possible that later applications in the field may be less effective. Furthermore, some of the herbicides, in particular, Regiment® and Clincher®, although showing biomass reduction at this early stage application (at least 60% in most cases), did not show 100% control of individual plants, which could recover later in the season. Further testing in the field or greenhouse is necessary to determine if that is the case. Again, this matches closely with grower anecdotal evidence in the field, where the unidentified watergrass appears to recover from applications of both Regiment® and Clincher®.
For growers, this preliminary screening implies that control of this new biotype/species will need to be prioritized early in the season, with an aim at overwhelming the plants' ability to metabolize the herbicides, as well as utilizing alternative modes of action. Some possible treatments (note: these have not been field-tested and could cause phytotoxicity) could be: a stale seedbed using a non-selective herbicide; pre-plant Prowl H2O® (pendimethalin) followed by post-emergent herbicide applications; pre-plant Abolish® (thiobencarb) followed by Cerano® or Butte® or Granite GR®; Cerano® followed by Butte® or Bolero® or Granite GR®; or Butte® followed by Granite GR® or Bolero®. There is still a strong likelihood that a follow-up application may still be required later in the season, even with these early-season applications.
Research with this unidentified species or biotype is ongoing, and another larger set of samples was collected in 2020. This larger set will also be subjected to a screening in the greenhouse, and results will be reported in 2021-2022.
Weedy Rice
Although we did not confirm any new biotypes in 2021 (data pending), we want to remain vigilant, as we continue to find new fields and acreage every year. For the latest, most up-to-date reports, please make sure to visit the California Weedy Rice website (caweedyrice.com) website, and subscribe to our Weedy Rice Email Updates (on the CA Weedy Rice website).
If you currently have weedy rice infested acreage, we recommend doing the following in 2021:
- If possible, fallow or crop rotate (with less water available this year, fallowing may be a good option)
- Use a pre-plant stale seedbed (flush the field, wait approximately 7-10 days for weedy rice to
emerge, then spray with glyphosate or other non-selective herbicide - Once weedy rice can be identified:
a. Hand rogue (make sure to pull plants completely out of the field and dispose of them)
b. If plants have fully headed, cut panicles off into bucket to avoid seed shattering
c. Spot spray (SUPPRESS® can be applied to a drained rice field, with a backpack sprayer).
Spray at rice early boot stage. See UC Rice Blog for more specific information. NOTE: no
other herbicides are labeled for spot spraying in California rice
In 2021, we would ask that growers and PCA's continue to give us a call if they suspect they have weedy rice in their fields. Please contact Whitney Brim-DeForest (wbrimdeforest@ucanr.edu) (Sutter, Yuba, Placer, and Sacramento), Luis Espino (laespino@ucanr.edu) (Butte, Glenn), or Michelle Leinfelder-Miles (mmleinfeldermiles@ucanr.edu) (San Joaquin). For Colusa or Yolo, contact either Whitney or Luis.
- Author: Whitney Brim-DeForest
We came up with a preliminary set of characteristics to distinguish this unknown biotype or species (we are unsure if it is a distinct species) from the typical barnyardgrass and late watergrass found in California rice fields. All were characterized by their seed size and awns (Table 1).
Preliminary Identification |
Seed Description |
Late watergrass |
Large size, no awns |
Early watergrass |
Large size, awned (all seeds) |
Barnyardgrass |
Small size, variably awned (some seeds have awns, some do not) |
New biotype/species (unknown) |
Small size, awned (all seeds) |
In 2018, we collected 8 samples from the field, and used two late watergrass samples from known susceptible populations to use as controls. We conducted a screening in the greenhouse, to see if we could replicate what we were seeing in the field. Field rates of Cerano® (clomazone), Butte® (benzobicyclon+halosulfuron), Granite GR® (penoxsulam), and Bolero® (thiobencarb) were used as the early-season granular applications. Field rates of SuperWham® (propanil), Regiment® (bispyribac-sodium) and Clincher® (cyhalofop) were used to test for the late-season cleanup applications. In the greenhouse, all applications were made at the 1.5 leaf stage of the grass.
Results indicate that 8 of the 8 samples were not controlled (less than 50% by biomass, in comparison to the untreated controls) by Granite GR® or Butte®. 7 of the 8 samples were not controlled by Bolero®, and 6 of the 8 were not controlled by Cerano®. This closely follows what growers were stating had occurred in the field: the watergrass was escaping early-season control, and was then difficult or impossible to control with later-season herbicide applications. SuperWham®, Regiment®, and Clincher® controlled 8 of 8 samples (at least 60% control). However, since the greenhouse application was conducted at an early timing (1.5 leaf stage), it is possible that later applications in the field may be less effective.
For growers, the implications of this preliminary screening are that control of this new biotype/species will need to be prioritized early in the season. Possible treatments (keep in mind that these have not been field-tested and could cause phytotoxicity) could be: a stale seedbed using a non-selective herbicide; pre-plant Abolish® (thiobencarb) followed by Cerano® or Butte® or Granite GR®; Cerano® followed by Butte® or Bolero® or Granite GR®; or Butte® followed by Granite GR® or Bolero®. There is still a strong likelihood that a follow-up application may still be required later in the season, even with these early-season applications.
In 2020, more than 60 watergrass samples were collected from all over the rice-growing region. We will continue working on identification and conduct further herbicide screening this year.
- Author: Whitney Brim-DeForest
- Posted by: Gale Perez
The UCCE Rice Team is conducting a field survey to collect watergrass samples over the next few weeks. The samples will be grown out in the greenhouse to help us start figuring out the identification and phenotypic characteristics (how to distinguish one from another) for the watergrass species found in California rice fields. The hope is that this will give us data for developing chemical and non-chemical management plans for watergrass, similar to what we have been working on with weedy rice over the past few years.
The project was funded by the California Rice Research Board, and is led by Whitney Brim-DeForest (UCCE Sutter-Yuba) and Marie Jasieniuk (UC Davis).
We are reaching out to ask for locations of rice fields from growers and PCA's, so our team can go out and collect seed. We are looking for all types of watergrass: "mimic", early watergrass, late watergrass, barnyardgrass (Figure 1), and the new species that we started seeing a couple of years ago (Figure 2). We hope to start collecting in the next week or two, through the end of September.
For more information, and if you are interested in having us come out and sample your field(s), please contact Whitney Brim-DeForest (wbrimdeforest@ucanr.edu), or call 530-822-7515.