BASF is stepping up its stewardship efforts for Clearfield rice to make sure the still-new technology is more than just a two- or a three-year wonder.
Introduced in 2003, Clearfield rice varieties and hybrids tolerant to Newpath herbicide were grown on about 564,000 acres in 2004. BASF and its seed company partners expect at least 700,000 acres of Clearfield rice in 2005.
But company representatives are urging growers not to become too exuberant in their adoption of the technology. Planting Clearfield rice in the wrong places, such as fields where it was grown last year, can lead to serious problems for the rice industry, they say.
“We have had some examples of outcrossing,” said Bruce Cranfill, product manager for Clearfield rice.
“We certainly knew it could happen theoretically, and we've had a case or two where it did happen in 2004. That just lends more credence to why we have to take stewardship seriously.”
Outcrossing refers to the herbicide resistance in Clearfield rice being transferred to red rice, creating a red rice biotype that cannot be controlled by the Newpath herbicide used in the Clearfield system.
University of Arkansas researchers and Extension specialists discovered a field in which outcrossing had occurred while conducting at-random sampling of fields of Clearfield rice last year.
“The resulting plant was a very large hybrid,” said Bob Scott, Extension weed scientist with the University of Arkansas. “There was a lot of hybrid vigor when that particular cross was made. It was very easy to see and very telling for someone like me who has been working with this technology since 1997.”
Speaking at a press briefing on Clearfield rice at the Mid-South Farm and Gin Show, Scott said that, in their sampling of rice fields, university specialists discovered a field that was in its second year of Clearfield rice, a violation of Clearfield's rotational guidelines, which require growers to rotate to another crop such as Roundup Ready soybeans.
“This guy did not do that and planted Clearfield 161 a second year,” said Scott. “He put on two applications of Newpath and came back with Beyond herbicide under Arkansas' Section 24c special local needs label.
“He ended up with quite a bit of red rice still left in the field. We sampled it and found through DNA testing and field testing that the previous year there had been an outcrossing event between Clearfield 161 and some red rice plants.”
The potential for large numbers of escapes of red rice in the year following an outcrossing event is the reason BASF and the University of Arkansas recommend that after one year of Clearfield rice growers rotate to soybeans or another crop that uses an alternative mode of action to Newpath, including Roundup Ready soybeans.
Scott said the grower also failed to strive to get 100 percent red rice control, another key component of the stewardship program for Clearfield rice.
“In the first year that he had Clearfield 161, he had a lot of application errors in that field,” said Scott. “It can be difficult to get two shots of Newpath on and not leave any streaks. If you have an area that just received one 4-ounce application of Newpath, you're probably going to have some red rice in that area.”
Scott said he doesn't believe it's the farmer who gets 97 to 98 percent control with two 4-ounce applications of Newpath who is more at risk for outcrossing of Clearfield varieties into red rice.
“I think it's the big streaks down through the field, the application errors, the corners that don't get sprayed. That allows a lot of red rice to go to seed with a lot of Clearfield rice. It's a numbers game that just improves the potential for outcrossing.”
The third component, he said, is saving Clearfield rice seed, another violation of BASF's stewardship guidelines.
“If you save harvested seed from that field, you are potentially putting that harvested seed right in the bag and spreading it to you neighbor's fields. And that goes for any field where you think you might have had outcrossing.”
Scott said he understands why some growers may be tempted to follow Clearfield rice with Clearfield rice despite the 18-month rotation restriction for returning to Clearfield rice.
“There's a lot of ground in Arkansas that won't grow soybeans or much of anything else,” he said. “It's very easy for farmers to look at those fields and say I can grow 160 to 170 bushels of Clearfield rice with no red rice in it, and I'm going to keep doing it until it doesn't work anymore.
“That's fine if he could keep the red rice on his farm, but weeds are biological entities and they have a tendency to spread where they want to spread. If one guy lets it go, it's going to spread to his neighbor and to his neighbor and to his neighbor. That's just how resistance works.”