Weedy Rice: Survey and Season Wrap-up

Weedy rice
2020 Survey Update

Weedy rice was found in California on a large scale in 2016, over 8 counties, after having been only found in a few fields in one county prior to 2008. In 2020, University of California Cooperative Extension conducted a comprehensive survey. The objectives of this survey were to determine: 1) presence-absence of weedy rice, 2) to determine infestation level, and 3) to determine if there was any pattern to the distribution of weedy rice biotypes.

A survey was conducted from June thru September 2020 across eight counties (Glenn, Butte, Colusa, Sutter, Yolo, Yuba, Placer and Sacramento). Each field was surveyed on an individual basin level. Each basin was surveyed by patrolling the parameter and visually and physically inspecting. All known biotypes (1 to 7) were recorded. Once the weedy rice was identified in the basin, a rating system was used to assess the level of the infestation from 0 to 6, with 0 being the absence of weedy rice, and 6 being 25% or more of the basin infested. The rating system (Table 1) was applied to each basin.


2020 Results Summary

The total acreage of basins found infested with weedy rice was 2,237; 20.7% of the basins surveyed contained weedy rice (Table 2). Biotype 1 was most common (54.5% of the basins) followed by Biotype 2 (30.9%). No basins were found with Biotype 5 or Biotype 7 (Table 3).

The majority of infested basins (34.7%) were rated infestation level 3 (less than 5 patches of plants), or infestation level 2 (27.4%) (less than 10 individual plants) (Table 4). None of the basins were rated at the highest infestation level 6.

a San Joaquin and Sacramento counties were not surveyed in 2020. Infested acreage is known from 2019 or previous years.




2021 Survey Update

In 2021, 39 fields were inspected for the presence of weedy rice. The total acreage inspected was 2,497 acres and the total acreage infested was 1,525 acres. The fields are in Yuba (1,506 acres), San Joaquin (985 acres), and Sutter (12.5 acres) counties.


2021 Samples Collected

We had lots of calls in 2021, but the vast majority were not weedy rice (not red pericarp, non-shattering). Many were off-types or varietal contaminants. Preliminary findings are: one previously-infested ranch in Yuba County with Type 5, three new ranches infested in Glenn County (2 with Type 5, and 1 with Type 1), and one previously-infested ranch in Butte County with two new biotypes (Type 2 and Type 3).

We encourage growers and PCA's to please continue calling us with suspected infestations, as the smaller the infestation, the easier it is to control it.

Call your Farm Advisor:


California Weedy Rice website


By Whitney Brim-DeForest
Author - County Director, Sutter and Yuba Counties and CE Rice and Wild Rice Advisor
By Luis Espino
Author - Rice Farming Systems Advisor & Butte County Director
By Troy Clark
Author - Rice Junior Specialist
By Gale Perez
Posted by - Program Representative