Start collecting California rice weed seeds for resistance testing

Whitney Brim-Deforest

Dr. Whitney Brim-DeForest, Extension Agronomist University of California, Davis

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 below):

• For watergrass species, this should be close to rice harvest (seeds should be brownish in color)

• For sprangletop, timing will be earlier, in August or September (seeds will appear greenish)

• For the sedges, timing may be as early as July, all the way through early September

• Smallflower umbrella sedge seed is yellow, with brown hulls (looks like dust)

• 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 in Biggs. If you need assistance in collection, please contact your farm advisor or PCA. Results should be emailed to you in March 2021.

The University of California contributed this article.