It's weed seed collection season! As weeds mature through summer and early fall, now's the time to gather seed samples from any herbicide-resistant species you've spotted in your fields.
How to know if what you are seeing is likely resistance (and what to collect):
- Weeds are located in clumps
- “Streaks” of weeds may be found going away from those clumps (dragged by field equipment)
- Weeds are not evenly distributed throughout the field
- Weeds are not found only around field margins
- There are no patterns to the distribution (indicating a clogged nozzle or skip)
What we test:
The UCCE Weeds Program regularly tests:
- Watergrass species (late, early, barnyardgrass, coast cockspur)
- Sprangletop
- Smallflower umbrella sedge
- Bulrush
- Redstem/Redberry
If you don’t see a species of interest listed above, that is okay! We welcome submissions of any species you suspect is herbicide-resistant.
Collection timeline & tips
Collect when seeds naturally fall off the seed head with gentle agitation in a paper bag. It is important not to strip the seeds from the seedheads or panicles, or the seeds will not germinate, and we will not be able to successfully have screening results.
Table 1. Overview of the optimal scouting timing and seed identification characteristics for four weed species.
Species | Best timing | What to look for |
| Watergrass | Near rice harvest | Brownish seeds |
| Sprangletop | August - September | Brown/dry seeds |
| Sedges | July – early September | Yellow seeds with brown hulls (dustlike) |
| Bulrush (roughseed) | Summer - fall | Black seeds with fine hairs |
Collection best practices:
- Sample from multiple plants (collect several handfuls minimum)
- Target areas you know were treated with the suspected herbicide
- Avoid field margins
- Dry samples in a paper bag to prevent mold (no plastic)
- Don't collect too early! Seeds need to be mature or they will not germinate
How to submit:
- Complete the form at agronomy-rice.ucdavis.edu (make sure to include your email!)
- Deliver your sample to a local UCCE Farm Advisor or directly to the Rice Experiment Station (RES) in Biggs
- Get results via email (typically in March of the following year)
Need help identifying which weeds to collect or how to sample? Reach out to your local UCCE Farm Advisor.