Red rice is a common weed in many rice growing areas around the world. It is a very difficult weed to manage because it is biochemically identical to commercially grown rice; therefore, herbicides that kill red rice also kill cultivated rice.
Red rice has kernels with a red pericarp that contaminate rice grain during harvest, severely reducing grain quality. Additionally, red rice competes with cultivated rice for nutrients, water and space, reducing rice yields.
Red rice is widely spread in the Southern U. S. rice producing states. In California, red rice has been identified in a few fields in Colusa and Glenn counties since 2003. The establishment of this weed in California constitutes a serious risk for the rice industry. Steps have been taken to eradicate this weed from infested fields; however, the true distribution of red rice in California is unknown.
To address this issue, a survey of fields surrounding infested fields in Glenn County was conducted during 2008. The objectives of this survey were:
• To delimitate the areas infested with red rice and estimate its expansion during the past few years.
• To collect plant material for genetic and phenotypic characterization.
• To select fields where management/eradication plans can be evaluated.
During September 2008, two scouts trained in red rice identification surveyed commercial rice fields surrounding known infested fields in Glenn County. Suspected red rice plants were transported to the Rice Experiment Station in Biggs for identification. During transport, plants were covered with plastic bags to avoid seed dispersal.
Survey results: The total area surveyed was approximately 14,500 acres. Only one field was positively identified as infested with red rice. Two other fields are suspected to be infested. Genetic analyses of the samples taken are needed to correctly identify them as red rice. Suspected samples taken in other four sites were identified as off-type rice plants.
The 2008 red rice survey showed that weedy rice is still present in Glenn County. However, its distribution within the surveyed area is limited and expansion seems to be reduced.
Managers of infested fields are making significant efforts to eliminate infestations. Another survey is planned for the 2009 rice season in Glenn and Colusa counties.