Growers target dangerous pest that looks just like rice

Rice farmers, researchers and seed certifiers have so far been able to contain weedy rice well enough to prevent the pest from causing economic damage—even though it has been documented in more than 2,200 acres in every growing area of California.

Weedy rice, which looks a lot like the real thing but produces reddish grain that shatters easily at harvest, has been devastating in the Southeastern U.S. and other production areas around the world.

"So far our growers have not had problems with the millers," said Luis Espino, University of California Cooperative Extension rice farm advisor in Butte County. "The purpose of all this research and these meetings is to keep it that way."

Espino shared his insights at the Weedy Rice Workshop this month. The event, held in Yuba City, was sponsored by UCCE and the California Rice Commission.

The first line of defense against this imposter that looks like rice is a strictly enforced requirement: Commercial producers must use certified seed, a condition that began two years ago.

In early August, a team of inspectors looked closely at 27,000 acres of seed production statewide to make sure no fields had so much as a single weedy rice plant.

"All of the seeds are certified to be free of weedy rice," said Timothy Blank, certified seed program representative at the California Crop Improvement Association. "Seed fields and seed lots are inspected, and we have zero tolerance for red or weedy rice."

Last year inspectors rejected more than 1,000 acres of seed production because the fields contained a combined total of just 25 weedy rice plants.

There is no tolerance for this pest because it is hard to identify due to its resemblance to rice. It's also hard to kill without damaging the surrounding crop.

"In Southern Europe, the Mediterranean and Africa, it is considered a major problem," Espino said. "By the late 19th century, some Louisiana fields had so much they just stopped growing rice in them." Growers are using seed certified to be weedy rice-free and generally scouting their fields for infestations. But there is concern that some may still be moving seeds from infested areas to clean ones on harvesters and other equipment.

"It would be good if we could get more people to not take equipment from infested areas to clean ones," said Whitney Brim-DeForest, UCCE rice advisor in Sutter and Yuba counties.

It can be challenging, however, to clean equipment well enough to avoid carrying a few weedy rice seeds to new areas.

Because any material that kills the pest would also kill the crop, hand rouging is the most widely used technique for getting rid of weedy rice once it is in a field.

Three years ago, researchers established test plots in Davis to learn more about how existing infestations could be reduced or eliminated more efficiently. They found the stale seed bed technique somewhat effective.

In the stale seed bed, weed seeds are germinated and the seedlings killed through herbicide applications or cultivation before the crop is planted.

"If you're going to get your weedy rice to germinate, you want to flush your field and then apply glyphosate," Brim-DeForest said. "Spray about 11 days after you apply water."

Growers can get 25% to 75% control of weedy rice with this technique, but there are seven types of weedy rice in California and type five germinates too slowly to be managed if growers apply herbicides or cultivate 11 days or so after applying water.

As researchers work to fine-tune the timing of the system of germinating weedy rice seeds and then treat the seedlings with herbicide, they have already confirmed that an organic alternative to glyphosate can be effective if it is applied early enough.

"We tried spot treatments with the biological herbicide Suppress," Brim-DeForest said. "When we applied Suppress at the late boot stage, the plants recovered, produced panicles, and some of them produced viable seed. But we did kill the plants with earlier timing."

There is a label restriction against applying Suppress in standing water, so the area must be drained before spot treatments. Its effectiveness in the stale seedbed system will be studied in future trials. Another technique that reduces weedy rice populations is continuous flooding through the winter after harvest.

"If you continuously flood year after year, you will knock the population down, but you have to keep your field flooded," Brim-DeForest said.

Growers are already scouting for weedy rice regularly. That, along with the use of certified seed, has significantly slowed the spread of weedy rice. Three new sites were reported last year in Sutter, Yuba and San Joaquin counties. But a survey of infested fields last summer revealed that earlier estimates of weedy rice, which totaled 14,000 acres in growing counties, were too high. That's because they didn't account for how much of a field has the pest.

"If we're talking about basins, not entire fields, we have a little over 2,200 acres with weedy rice," Espino said.

Scouting and controlling weedy rice is complicated by the weed's ability to cross with different rice varieties to produce hybrid weeds, each with distinctive appearances.

"We think we have seven biotypes in California," Espino said. "This is not bad. In the South, they have pages of biotypes."

Fortunately, around 95% of the weedy rice in California is of biotypes one, two and three, which makes identification a little simpler.

These three biotypes usually stand out in a rice field because the plants are taller than the crop, but positive identification can still be difficult.

(Bob Johnson is a reporter in Sacramento. He may be contacted at bjohn11135@gmail.com.)