Red rice poses a serious risk to the California rice industry and has the potential to impact rice yield and quality if this weed is allowed to spread and establish populations throughout rice fields in the state. This weed is prevalent in all of the southern U.S. rice producing states and continues to be a major constraint to production there.
Red rice is a member of the same species (Oryzae sativa) as cultivated rice grown in California. The name “red rice” refers to the distinguishing red bran that covers the kernels of red rice grain. Red rice is problematic because of the weedy characteristics it exhibits. This weed has a vigorous growth and tillering habit that makes it a better competitor for space and resources than cultivated rice varieties. Competition for these resources leads to reduced rice yields. In addition, red rice has an asynchronous reproductive cycle in which heading may occur over a prolonged period of time producing seeds that shatter easily at maturity. Seeds that fall to the soil surface may germinate when conditions are favorable or remain dormant for several years before germinating. Dormancy of red rice seeds leads to some challenges in developing an effective management strategy for this weed. In addition, chemical control of red rice during a rice cropping season is difficult since this weed is the same species as cultivated rice.
Red rice is also a cause of concern at the mill. The presence of red rice can lower the grade of milled rice. For example, there is a maximum limit of 0.5% red rice and damaged kernels (singly or combined) for Grade U.S. No. 1. Removing the red rice seeds at the mill may be done using optical sorters and additional milling but may increase the cost to the miller and result in a reduced price for the producer.
Many of you are aware that red rice has been identified in a couple of Colusa and Glenn County fields since 2003. So far this year red rice has been identified in fields where it occurred in 2005 as well as in one field that was not known to be infested last year. Growers with identified red rice infestations have been proactive and aggressive in removing red rice plants from fields prior to heading and should be commended for their actions. The rice industry as a whole must show this same dedication if we are to gain the upper hand on this pest.
UC in conjunction with growers, County Agricultural Commissioners, the California Rice Experiment Station and the California Rice Commission has been working to develop effective management strategies for infested fields. Thus far these plans have shown promise in reducing red rice populations in infested fields but it must be realized that there is no quick fix for this pest. Seed dormancy of this weed makes this a multi-year endeavor in cleaning up a field.
Red rice has the potential to have a serious economic impact on the California rice industry through reduced yields and quality as well as the costs associated with management of this weed. Although the presence of red rice is not a quarantine issue the California rice industry must be proactive if we are to effectively manage this pest and prevent the more widespread dissemination and establishment of red rice. One of the most important contributions you can make to the industry at this time is to scout your fields very closely for the presence of red rice. Prior to heading, red rice may be mistaken as watergrass escapes because it is about a foot taller and lighter green in color than our calrose varieties. Upon closer examination, it is apparent that the red rice plants are in fact rice and have prominent ligules and auricles that are absent from watergrass plants. Leaves of red rice plants are also much longer and rougher to the touch than our calrose varieties. It is impossible to accurately identify red rice from your pick-up so please take a closer look at any weeds that seem suspicious.
If you suspect you have/had red rice in one of your fields please contact Chris Greer, UC Cooperative Extension Advisor, for help with identification and developing a monitoring and management plan. (Contact Chris at 530-458-0578 or firstname.lastname@example.org)