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 has 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 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 2019.
I have been to several farm calls in the past few weeks with this weed (pictured below). I have seen 7 fields between last year and this year that appear to have bad infestations of this new watergrass species (Echinochloa spp.). We are unsure of the exact identification yet, but we know it is in the watergrass family.
The weed is maturing around mid- to late-July. It is small-seeded, and the awns are long and purple. All of the plants I have seen so far have seed heads that are completely awned, which makes it different than barnyardgrass (which has seed heads that are variably-awned).
How to ID:
o Every seed head has awns (unlike barnyardgrass)
o Should already be headed (by mid- to late-July)
o Awns are purplish in color (see photos)
o Seeds are small (smaller than late watergrass)
Please call Whitney Brim-Deforest (541-292-1553) or Luis Espino (530-635-6234), if you suspect that you have this weed in your field. We would like to collect seed samples to see what can be done to control it.
Photo 1. Seed head of unknown watergrass species (Echinochloa spp.) Notice visible purple awns.
Photo 2. Seed heads of unknown watergrass species (Echinochloa spp.) Notice visible purple awns, which can be seed before seeds are fully mature.
Photo 3. Full plant sample of unknown watergrass species (Echinochloa spp.). This plant headed in late July.
As many of you are aware, many of our grass species in California rice are resistant to multiple herbicides. Late watergrass aka "mimic" (Echinochloa phyllopogon), early watergrass (E. oryzoides) and barnyardgrass (E. crus-galli) are among some of our most competitive weed species, causing large yield reductions when uncontrolled.
One of the last remaining chemicals that our grass species are not yet resistant to is pendimethalin. Commercial formulations for pendimethalin registered for California rice are Prowl H2O and Harbinger. Prowl H2O is a delayed pre-emergent herbicide applied onto dry, drill-seeded fields. Harbinger is also a delayed pre-emergent herbicide, but the Harbinger system can be used in fields that are seeded by air. Both are viable uses of the chemical, and which one you choose will depend on your available equipment. For more information on how to apply, refer to the product labels.
Although I have used Prowl H2O in field trials and have a pretty good idea of its efficacy, I was curious to see how Harbinger looked in the field, since I have not yet had the opportunity to use it in a trial. I recently visited Rice Researchers, Inc., a rice breeding facility in Glenn County, where they are using a Harbinger-based program, for the second season. The photo (below) shows the rice at about 30 days after seeding. No weed species were present in the field. This is after one delayed pre-emergent Harbinger application.
It is too late to utilize pendimethalin this season, but for help incorporating pendimethalin into your herbicide plan for 2018, talk to your PCA, or give one of the UCCE Rice Advisors a call. Especially for growers that have herbicide resistant grasses, it can be a valuable tool in reducing grass populations.
It may be a bit early in the season to start thinking about herbicide resistance, but in just a couple of weeks, most rice growers will have put out their last herbicide applications, and it will be time to start scouting.
University of California Cooperative Extension, in collaboration with the Agronomy Research and Information Center at UC Davis, has produced a short video which explains how to collect seed to make sure that if you do submit weed seed for testing, you get back accurate results. The form which must accompany any submitted weed seeds can be found on the UCANR Rice Website: http://rice.ucanr.edu/files/263785.pdf.
I went out on a few farm calls in the past week, and have noticed a trend. Due to the unusually wet weather this spring, some of the weeds are already producing seed out in the field! This occurs when the field was moist or wet in the spring, and was not tilled or sprayed prior to planting.
If you have weeds that are already setting seed, follow the steps below:
1) First, make sure to get proper identification of the weed species. Some weed species will produce seed and that seed can germinate and send up a second flush of weeds, in the same season! They are:
- Smallflower umbrella sedge
- Mexican sprangletop
NOTE: There are two types of sprangletop: Mexican and Bearded. Only the Mexican sprangletop will set seed that will germinate this season. Bearded sprangletop seed is dormant and won't germinate until the 2018 season.
2) If you have one of the above-listed species that is already setting seed, it is important to make sure that your follow-up herbicide application will control this second flush of germinating seeds. Otherwise, the amount of seed produced and deposited into the seedbank will be exponentially higher than in a normal year, because there will be two generations of plants that set seed in the same season!
3) If you have a weed species setting seed that is NOT listed above, you will likely not be able to do much this year, as the weeds are likely too large to control with herbicide and any impacts on yield have already occurred. Plan to have an aggressive program for next year (2018)!