Researchers Continue Work to Address Rice Weeds in California

Brian German Field & Row Crops, Industry

Researchers with the UC Cooperative Extension (UCCE) are continuing their work to help growers address various rice weeds in California. The team is focused on weedy rice, sprangletop, and watergrass concerns. Industry members were recently given an update on the progress made during the 2020 California Rice Virtual Field Day. A weedy rice trial now in its second year is helping researchers formulate a better management approach.

rice weeds

“Hopefully with being able to better understand when the weedy rice comes up in the field and also under what conditions – whether it comes up under flooded conditions versus flush conditions – we can guide growers better on what will get it up faster and then how to treat it once it comes up,” said UCCE Rice Advisor Whitney Brim-DeForest.

The weedy rice experiment is being conducted at UC Davis. After establishing the field during the first year, the trial is starting to show promise. Data is being generated on the speed of the emergence of different biotypes undergoing different treatments. The team has seen some success working with SUPPRESS herbicide. However, there is a slight limitation to the product as it relates to spot spraying.

“It is okay to use but growers have to make sure that they use it when there’s no standing water in the field. It is only labeled for use in rice if you drain the field before application,” Brim-DeForest noted. “We’re working with the company to get the label hopefully amended for next year.”


Sprangletop continues to be one of the most troublesome rice weeds for California growers. The problem appears to have become more widespread over the past two to three years. Brim-DeForest hypothesized that it may be due to application timing early in the season. A lack of management materials also compounds the issue.

“If you miss it with your first herbicide application there’s really only one option to apply later in the season, so that’s part of the issue as well,” said Brim-DeForest. “We’re not catching it early and then there are not that many options to control it later on in the season.”


Adding to the issue of California rice weeds is a new type of watergrass that is giving growers problems. It appears to be either a new species or a new biotype of watergrass that is not being adequately controlled by registered herbicides. Brim-Deforest suggests using a stale seedbed approach for severe infestations of both watergrass and weedy rice issues.

“If there’s no registered herbicides that are working during the cropping season this can be a good technique,” Brim-Deforest explained. “it’s a good trade off because you’re getting a lot of weed control, so therefore spending less on herbicides during the season.”

Brim-DeForest also reminds growers to always read and follow all label instructions no matter what approach is taken. It is also advised to consult with local Agricultural Commissioners in regard to buffer zones and aerial restrictions.

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Brian German

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Ag News Director, AgNet West