UC confirms 6 weedy rice samples; survey updates infested acreage

weedy rice biotype 5
Weed rice biotype 5 is tall, awnless, has straw hull color and has purple-colored nodes — photo courtesy UCCE

During the 2020 season, 31 new suspected weedy rice samples were received and six were confirmed to be weedy rice. Three came from new sites in Sutter, Yuba and San Joaquin counties.

The other three came from already infested fields. Additionally, we received five samples that could not be identified and need to be tested in the lab to evaluate shattering and dormancy; results will be shared in 2021.

A few seed fields were found contaminated with weedy rice during the seed certification process (primarily with Type 5, seen above); these fields were not approved for seed and the grain marketed as paddy instead.

This summer, we conducted a survey of all weedy rice infested fields found between 2016 and 2019. The survey allowed us to update our records and determine the degree of infestation on every field.

For each field, we recorded how many basins were infested and their acreage. By recording only infested basins, we now have a better estimate of the acreage infested in California.

Out of 11,000 acres of inspected fields, only 2,300 acres were recorded as infested. We found that several previously infested fields seem to be free of weedy rice. This reduction is in part thanks to the efforts of many growers and pest control advisors implementing measures to clean up the fields, such as roguing, fallowing and rotating crops.

To date, seven weedy rice biotypes have been identified in California. For more information, visit https://caweedyrice.com/.

The University of California Cooperative Extension Rice Team contributed this article.

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