A worldwide pest

International conference highlights the need to remain proactive against weedy rice.

• By Luis Espino •

Luis Espino

University of California
Rice Systems Adviser

This February, I had the opportunity to travel to Pelotas, Brazil, to attend the Seventh International Temperate Rice Conference. The meeting brings together temperate rice-producing countries to share information on rice issues and ongoing research.

Attendees included rice scientists from Uruguay, Chile, Argentina, Italy, Brazil, Russia, Australia and the United States. In addition to the technical presentations, we had a chance to take a field trip to see some rice fields and research plots.

During the technical presentations and field visits, one issue kept coming up as a major production constraint in all participating countries: weedy rice. In the area of Brazil where the conference was held, the state of Rio Grande do Sul, rice-production practices revolve around managing weedy rice.

Rotation and herbicide-tolerant varieties

For them, rice fits in a larger system where fields are also rotated with soybeans or pasture. This helps them tremendously with managing weedy rice. When I would mention that in California, most rice is not rotated with other crops, other attendants were extremely surprised and wondered how weedy rice is not a major problem.

In addition to rotation, Brazilian growers rely heavily on herbicide-tolerant rice, the same technology used in the southern United States to control weedy rice. We visited several trials comparing varieties tolerant to herbicides that kill weedy rice but not cultivated rice.

fullpage brazil

University of California’s Luis Espino visited rice fields and research plots in the state of Rio Grande do Sul, located in southern Brazil north of the Uruguay border. Rice producers there rely heavily on crop rotation as well as herbicide-tolerant varieties — photo by Dr. Luis Espino, UCCE

Even with these tools, weedy rice remains a big problem for Brazilian growers. During the field visit, it was not difficult to find some off-type rice plants growing in rice fields. I cannot confirm they were weedy, but they certainly looked suspicious.

From hearing the technical presentations and talking to scientists, it is clear to me that most countries rely on rotation and herbicide-tolerant rice to combat weedy rice. These strategies are limited (rotation) or absent (herbicide-tolerant rice) in California.

Need to remain vigilant

Nevertheless, weedy rice has not become the big issue in California it has in other parts of the world — but it certainly has the potential to become one. California rice growers have the capacity to minimize the impact weedy rice will have on their industry by continuing to grow certified seed and remaining vigilant so early infestations are quickly addressed and eliminated.

I believe weedy rice is an issue that will stay with us for a long time but can be minimized if everyone working in the industry — researchers, Extension, consultants and growers — keeps their focus and continues to be proactive for years to come.

Dr. Luis Espino is a University of California Cooperative Extension rice systems adviser for Butte and Glenn counties. He may be reached at laespino@ucanr.edu.