Weedy Rice: Survey and Season Wrap-up

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.

Table 1. Rating system utilized for visual assessments of weedy rice infestations. Basins were rated individually.

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.

Table 2. Weedy rice infestations in 2020 per County, acreage surveyed, acreage infested, and percent of acreage infested (%).

Table 3. Weedy rice infestations (2020) per individual weedy rice biotype in acreage surveyed and percent of acreage infested (%), where total acreage was 2237 ac. No acreage was found infested with Biotypes 5 or 7.

Table 4. Weedy rice infested acres (2020), percent of infested acres, and percent of total acres surveyed. Total infested acreage was 2237. Infestations were rated on a scale of 0 to 6.

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:

• Michelle Leinfelder-Miles (San Joaquin County)
• Luis Espino (Butte and Glenn Counties)
• Whitney Brim-DeForest (Sutter, Yuba, Placer, and Sacramento Counties)
• For Colusa and Yolo Counties, please call either Whitney or Luis.

California Weedy Rice website