Weedy Rice—Not as Simple as it Sounds

Weedy Rice is A Pesky Rice Type in Production Rice Fields

By Mikenzi Meyers, Associate Editor

Contrary to its name, weedy rice is not in fact weeds in rice—but it is presenting several challenges to California rice growers. To help farmers combat the pesky variety, UC Davis Ph.D. student Liberty Galvin and the horticulture and agronomy graduate group have conducted extensive research.

According to Galvin, the genetic and physiological properties of weedy rice are the same as the cultivated varieties consumers typically eat. So what’s the issue? Galvin said that besides the fact that weedy rice is off in its coloring, it’s nearly impossible to harvest.

“The issue is that the seed shatters, or basically falls to the ground. So when you go through and try to harvest it, the grain does not get collected in the harvester,” Galvin explained.

Although right now it seems that commercially growing weedy rice is not an option, there are ways to prevent it. Galvin’s research found that drilling the seeds at least two inches into the soil will eliminate seed germination or emergence in the field. This is especially useful in California, where tillage is done only to prepare the field, not plant the rice itself.

Galvin said that while growers can produce their own rice seed, it has to be certified by the California Crop Improvement Association or a Rice Seed Quality Assurance Program.  In all cases, growers are required to plant only certified rice seed so there is no opportunity for traces of weedy rice to enter the soil.

“That is why tillage depth is so important, because that’s how you reduce your seed bank,” she said.

Weed Control in Rice Fields

Controlling Herbicide-Resistant Weeds in California Rice Fields

By Emily McKay Johnson, Associate Editor

Whitney Brim-DeForest, UC ANR Cooperative Extension rice farm advisor for Sutter, Yuba, Placer and Sacramento Counties in California, currently works in all rice production areas across the state to identify problematic weeds in rice fields.

Given her background in weed science, Brim-DeForest explained California rice growers flood their fields for weed suppression, as well as use herbicides for weed control and management. “I’d say that we do have quite a few herbicides right now. As we continue to get new herbicide resistant weeds every year,” said Brim-DeForest, “we are starting to run out of options, especially for some growers who encounter herbicide resistance.”

Brim-DeForest believes herbicide resistance was first discovered in the early 1990’s, but “has become significantly problematic for growers within the last 20 years. Because of the herbicides we use and the limited number that we have, we have ended up with an increasing number of weeds that are herbicide resistant every year. Since about 2000,  we’ve had a new species or herbicide that encounters resistance every year,” she stated.

Brim-DeForest treats a multitude of weed species in her line of work. “I would say the watergrass species is our biggest problem,” she noted. “We also have a weedy red rice that was discovered in the early 2000s. It is not widespread, but we do have a few fields with it,” she explained.

Featured Photo: Whitney Brim-DeForest, UC ANR Cooperative Extension rice farm advisor.