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Red flag warning
Follow stewardship plan to prolong |
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By Vicky Boyd |
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The first confirmed commercial case of Clearfield rice outcrossing with red rice should act as a wake-up call that an herbicide-tolerant weed is not only possible, it’s a reality, say university weed experts and BASF representatives. The case also points out the need to strictly follow BASF’s Clearfield stewardship agreement, which recommends removing all escaped red rice plants and planting only one year of Clearfield rice before rotating to a non-rice crop, says Bruce Cranfill, BASF market manager for Clearfield rice. The field in question had been planted for two consecutive years in Clearfield rice, and red rice plants that had escaped treatment in 2003 had not been removed before harvest. No surprise “We knew through university models that it [out-crossing] did exist,” Cranfill says. Bob Scott, University of Arkansas Extension weed specialist, agrees. “Early on, I would have been really surprised. But in the last three to four years, there have been a lot of people who have done plot work with Clearfield, and they noticed out-crossing in their plot work,” Scott says. “Things kind of changed. Most people had thought it would be seven or eight years before it showed up as a significant issue. The thinking has turned to it’s going to happen sooner than later.” What is out-crossing? The University of Arkansas began a red rice sampling program in 2004 to catch just such outcrossings, Scott says. Fields that had been in Clearfield rice for two years, had red rice escapes or for other reasons were suspected of possibly having outcrossing were targeted. Red rice samples from more than a dozen fields were collected during the past season, and these samples are currently being analyzed, Scott says. The lone confirmed case of outcrossing occurred in 2004 in a Jackson County field in northeast Arkansas, Scott says. And it was actually discovered by a private consultant, whom the farmer contacted, and outcrossing was confirmed by BASF company researchers. That field is now included in the university program. The grower had planted Clearfield 161 in both 2003 and 2004, a practice that goes against BASF’s stewardship recommendations. The grower left red rice plants that escaped treatment in his field, which also goes against BASF stewardship recommendation to remove escapes. Although the stewardship recommendations are important to help minimize red rice outcrossing, probably more critical is what growers do to a Clearfield rice field the following year, says Steve Linscombe, Louisiana State University AgCenter’s southwestern regional director and an LSU rice breeder who helped develop the Clearfield line. It’s not a matter of if—it’s a matter of
when “I think you have to go in with the assumption that even with as good a job as you can do, there will be a handful of red rice plants that escape control,” Linscombe says. “The best thing is to come back with Roundup Ready beans or fallow plow where you can eliminate those plants before they set seed for the following year. “The worst thing you can possibly do is to follow Clearfield
rice with Clearfield rice, because if you do have outcrossing, say in
2003, and you come back [with Clearfield] in 2004, you know those red
rice plants are not going to be controlled. They will go set seed and
drop that seed again. The amount of resistant seed is going to increase
exponentially.” “The seeds that are in those plants may or may not have outcrossed with red rice—you can’t tell from just looking at them that first year whether anything is going on,” Scott says. During the 2004 season, the grower noted that two 4-ounce Newpath applications followed by a Beyond application didn’t control some of the red rice in his field. BASF reps visited the field and conducted a field bioassay, where they sprayed the suspect plants with a higher-than-labeled rate of Beyond herbicide. When the plants survived the treatment, the reps sent samples to the company’s Raleigh, N.C., laboratories for genetic testing. The testing confirmed that the tolerant red rice plants contained DNA from Clearfield rice, Cranfill says. The tolerant red rice plants towered over surrounding rice and even nearby susceptible red rice plants by 1 to 2 feet. Growers have since dubbed the tolerant plants “bull” red rice. The tolerant red rice, which was scattered randomly throughout the field, also appeared to mature later than the conventional rice. If the problem had not been caught, Scott says the next generation of tolerant red rice would have been “really scary.” “It comes in 20 different shapes and sizes, with a smooth leaf or a rough leaf, 1 foot tall and 5 feet tall,” he says. “There’s a lot of genetic diversity. It gets even more difficult to tell whether you have outcrossing.” The University of Arkansas, in conjunction with BASF, has recommended that the grower in question burn the field to singe existing seed heads or use another method to destroy any surviving plants. They also recommend that the field be fallowed or rotated for at least two years to a non-rice crop, such as Roundup Ready soybeans, where volunteer red rice can be controlled with a mode of action different than Newpath. Contact Vicky Boyd at (209) 571-0414 or vlboyd@att.net. Internet Hotlinks University of Arkansas rice variety performance trails, 2002-2004
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