It's that time again! If you would like to submit seeds for herbicide resistance testing, many weed species will be maturing right about now.
The UCCE Rice Weeds Program tests grower submitted seed samples of potentially herbicide-resistant watergrass species, sprangletop, smallflower umbrella sedge and bulrush. However, we encourage you to submit ANY species that you suspect to be resistant. We keep individual grower information confidential and any reporting of results will not identify individual growers.
Please fill out the form (linked here) for each weed seed sample (each field and/or species). The following tips will ensure that you receive the best possible results:
- The best timing of collection is when the seed easily falls off the seed head by gentle agitation in a paper bag (see video for demonstration):
o For watergrass species, this should be close to rice harvest (seeds should be brownish in color)
o For sprangletop, timing will be earlier, in August or September (seeds will appear greenish)
o For the sedges, timing may be as early as July, all the way through early September
o Smallflower umbrella sedge seed is yellow, with brown hulls (looks like dust)
o Bulrush (roughseed) seeds are black and have small hairs
- Seed should be collected from areas that you know have been sprayed with the suspected herbicide.
- Collect seeds from multiple plants, and the amount should be at least a few handfuls of seed, to ensure sufficient quantity for testing.
- Please do not collect seed from around field margins.
- Allow seed to dry in the paper bag to prevent molding.
Bring the sample and form to your local UCCE Farm Advisor (Whitney, Luis, or Michelle) or send or drop off samples at the Rice Experiment Station (RES) in Biggs. If you need assistance in collection, please contact your Farm Advisor or PCA. Results should be emailed to you in March of 2021.
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 (firstname.lastname@example.org), or call 530-822-7515.
- Author: Whitney Brim-DeForest
- Author: Roberta Firoved
The labeled weeds that RebelEX®controls are sprangletop, watergrass (both early and late), barnyardgrass, ricefield bulrush, Monochoria, redstem, ducksalad, California arrowhead, and water plantain. It does not have a water-holding period. The application timing begins from when the rice has one leaf or more, up to 60 days before harvest. Efficacy, as with most products, is better when the weeds are smaller. For flooded fields, it is important to have maximum contact, so it is recommended to lower the water in the field until at least 70% of the weed biomass is exposed, before application.
The product is “rainfast” (meaning it isn't affected by water) within 2 hours, so reflooding quickly is recommended. The label recommends restarting the flood at 3 hours after application, and to have the field completely reflooded within 24 to 48 hours at a maximum. Long drainage periods can encourage additional germination of certain weed species, including smallflower umbrella sedge, watergrass, barnyardgrass, and sprangletop.
Since RebelEX® also contains penoxsulam, it cannot be applied in the same season as Granite GR® or Granite SC®. Doing so will cause significant phytotoxicity to the rice, and will likely impact yields. Clincher® can be applied in the same season, but depending on the rate of RebelEX® applied, the Clincher® application rates will vary, so please refer to the label for rates and timings if planning to also apply both herbicides in the same season. For management of resistance, however, it is not recommended to apply Clincher® and RebelEx® in the same season, as both contain the same active ingredient, cyhalofop. Repeated applications of the same active ingredient (cyhalofop) will select for resistance in sprangletop, barnyardgrass, and watergrass (both late and early).
Remember to always follow all label instructions when applying any pesticide, as the label is the law. Make sure to pay particular attention to the Use Precautions and Restrictions. Consult your local Agricultural Commissioner's Office regarding buffer zones and aerial restrictions, before making any applications.
The impetus behind the weed survey is due to the increasing numbers of new weed species that have appeared in the past several years: winged primrose-willow, weedy rice, monochoria, and recently, one (possibly two) new watergrass species. We are hoping that by conducting a survey, we may find some new species before they spread, and better establish ranges for the species we know we have.
A crew of two people will be stopping in random fields in the major rice-producing counties. We will take soil samples from the top six inches of soil in each field. The soil samples will then be processed in a greenhouse at UC Davis, where the weeds will be grown out to identify each species present in the soil. The reason we are surveying this way, instead of surveying during the rice-growing season, is due to the use of herbicides during the season, we would have difficulty seeing the presence of weed species that are well-controlled by the herbicides.
The 2019 Rice Weed Course will take place:
Friday, September 6, 2019
from 8:00AM to 4:10PM (Registration begins at 7:30AM)
Hamilton Road Field (on West Hamilton Rd. between Hwy. 99 & Riceton Hwy.)
and Rice Experiment Station, Biggs, CA
This year will mark the third rice-specific weed course at the Hamilton Road Field and the Rice Experiment Station in Biggs, CA on Friday, Sept. 6, 2019. The day will begin with an interactive field tour of the research plots (Hamilton Road Field) where attendees can get up close to the weeds and rice (bring your boots!) The course will include a hands-on weed identification session on emerging and mature weeds. In the afternoon, speakers will address several pertinent topics in CA rice, including algae, weedy rice, regulatory update, best management for grasses, and how to construct a weed management program. This course is a great opportunity to interact directly with the UCCE and UC Davis Rice Weed Research Team!
For a full agenda and registration go to:
For questions, please contact Whitney Brim-DeForest at 530-822-7515, or by email at email@example.com
Credits for PCA, QAC, QAL, Private Applicator: 6.0 other, 0.5 laws
CA Certified Crop Adviser: 6.0 IPM