The red rice out-crossing tour stop was a lively one for Nilda Burgos. It turned out many at the recent Southeast Research and Extension Center field day in Rohwer, Ark., were interested in the University of Arkansas weed scientist's research.
Why so many questions from the gallery? Because Burgos said that not all red rice is the same and red rice type might dictate some control practices.
Pointing at a series of red rice-infested plots behind her, Burgos said, “What you're looking at are survivors of two applications of Newpath at 8 ounces. These are plants from red rice seed we collected from an experiment last year that involved two Clearfield cultivars: CL161 and CL XL-8.”
Along with those were a dozen types of red rice. The 12 types come from three different zones in Arkansas: the White River area, the Grand Prairie, and the Delta.
“We put them in this experiment because they're flowering at different times. The largest group of the White River red rice flowered 84 days from planting. The Grand Prairie red rice flowered about 100 days from planting. The south Delta red rice flowered 105 days from planting. In all zones, of course, there were late and early types.”
The types of red rice range in height from 40 inches to 63 inches.
“So, these types were planted from mid-April to late May last year in the middle of CL rice. We harvested seed from those, which we planted this year. After treating the seedlings with Newpath, the survivors this year ranged from zero to 5 percent.”
There are also differences in the number of red rice survivors based on parentage.
“How much of a difference, we'll find at the end of the season when we sort out the plants to make sure they are, indeed, out-crosses.”
Burgos and colleagues have also surveyed commercial fields where Extension agents — under the leadership of Bob Scott, Arkansas Extension weed specialist — collected red rice seed samples in 2004 for testing in 2005.
“In strawhull red rice-infested fields we detected, on average, 100 plants per 100,000 that survived two applications of Newpath.
“On average, a field infested with blackhull red rice had about 450 plants per 100,000 that survived two Newpath applications. There is a clear difference among red rice types and how much out-crossing they can produce.”
Burgos also observed red rice that can flower from 65 days after planting all the way to 130-plus days after planting.
“That's a wide range. So whenever there's a case with red rice that flowers early, it's less likely (a candidate) for out-crossing. That's also true for red rice that flowers late. But the cases of red rice flowering in the middle of that range are (worrisome) because they're (more likely) to flower together with (commercial rice).”
Asked about her feelings on red rice survivor rates, Burgos admitted there are situations that evoke fear.
“After we verify these numbers and it brings us to, say, just 5 percent survivors between Clearfield and red rice, it is scary. That's quite a few plants surviving.”
To illustrate this further, Burgos pointed to three plots of progenies from blackhull red rice planted at the same seeding rates in late April 2005.
“But they're from different regions of the state. Look at the major differences in survivorship.”
Anticipating this, researchers have geographic coordinates for each red rice sample. “Once we sort out all the data, we'll be able to say, ‘Okay, this type has the most survivors and it's from this location.’ We can alert those farming that area about this case. Or, we'll tell them this other type is expected to produce X number of survivors if this type of Clearfield is planted.
“That should be very helpful for farmers. And that's a major goal of the project — to be able to go back to a grower and tell him the risk and behavior of red rice in his area. Hopefully, we'll be able to get this information (out) soon. That should allow much better management decisions.”
However, the data-gathering process hasn't been accomplished overnight. Burgos started work on aspects of red rice characterization in 2000 and the red rice/Clearfield out-crossing monitoring project has been going on since 2004.
Following Burgos' presentation, Scott spoke on the importance of her work. “If you go through this stop and don't start thinking about out-crossing and stewardship, something is wrong.
“If you've got a lot of red rice that's survived Newpath or even Beyond, it should worry you. At least consider rotating that field to soybeans for a season. Use some kind of resistance strategy.
“If out-crossed red rice gets out like regular red rice is now, I don't think it'll be the death of the Clearfield technology because of the other weed-control aspects of it. But it'll certainly remove the most important component of it. Please be aware of that.”