Herbicide-resistant rice available

The first lines of herbicide-resistant rice will be available for commercial planting in the Mid-South and Texas next spring.

Three Clearfield rice varieties resistant to Newpath (imazethapyr) will be available through Horizon Ag and its Orygen seed marketing group. The Orygen system includes 22 Southern seed companies.

The varieties have been in university variety trials for the past two years. Two were released for seed increase production last year:


CL121, a very early, semi-dwarf variety. According to Horizon Ag, it displays characteristics similar to Cocodrie, but is shorter and four to six days earlier. Milling results are good. The variety seems to be susceptible to sheath blight, blast kernel smut and straight-head. Performance indicates good adaptability across the entire Southern rice-growing area.


CL141 is a very early, traditional height variety with good yield potential. It most resembles Drew, but should reach maturity and 50 percent heading eight to 12 days earlier. Lodging potential and seedling vigor are similar to Drew. Mill results are very good. CL141 seems to be susceptible to sheath blight, kernel smut, straight-head and blast. Preliminary results indicate excellent second-crop potential due to its earliness and yield.


In addition, CL161 was released in mid-November 2001. The variety appeared in university trials as CFX 18. It is an early, semi-dwarf, long grain variety, close to Cypress in appearance, but reaches 50 percent heading 1-2 days earlier.

According to Horizon, there will be good supplies of CL121 and CL141 and very limited supplies of CL161. The varieties are adapted to all the Southern U.S. rice-growing states, including Texas.

In the spring of 2000, EPA approved a two-year, Section 24c label for BASF's Newpath, which is from the imadazilinone class of herbicides. A full Section 3 registration for the herbicide is expected soon. At the time of this writing, the Clearfield rice technology was at a final legal hurdle, Canadian clearance for the import of the rice as a commodity.

Newpath controls a wide array of weeds, including barnyardgrass, yellow nutsedge, broadleaf signalgrass, smartweed, goosegrass and red rice.

Because red rice and commercial rice are closely related, the potential for outcrossing (creating herbicide-resistant red rice) is significant. So, Horizon Ag and BASF are implementing a strict stewardship program for Clearfield rice seed, including a prohibiting saving seed to replant.

According to Dwight Cowan, chief executive officer of Horizon Ag, there's more to the seed piracy policy than insuring the company's annual seed sales.

“The main component of the stewardship program is to prevent outcrossing,” he said. “The way to do that is to make sure that all our seed production is absolutely clean and that there is never a potential for outcrossing on the seed production side. That's a big focus for Horizon.

“We ask that growers not harvest and save seed and replant it. If you have any red rice in the field that has had the potential to outcross, in a very short time, you will have lost the core value of the technology. You will no longer be able to control red rice on your farm. So we ask the grower to buy only certified seed every year.”

Growers must undergo certification before they can purchase Clearfield rice. Horizon and BASF scheduled a series of retailer training meetings in November and started the grower certification process in late November, according to Cowan. “Growers will get all the information on how best to manage the varieties and the weed control technology.”

Bob Scott, BASF technical service representative for Arkansas, said a key points of the training sessions “is to make sure everybody understands that this is a system. You purchase the seed and the chemical and unless you use them together, you're not using the system.”

The system includes two 4-ounce applications of Newpath, one applied in the soil either ppi or pre-emerge, followed by another application at early post.

“You have to put the soil-applied application down (Newpath) and if you don't get a rain, you have to flush it for activity,” Scott said. “Then you have to make that second-shot post. If you don't, you could have failures in red rice control.”

The discovery that led to the development of the Clearfield technology for rice occurred in the 1990s when Rice Research Station scientist Tim Croughan (Crowley, La.) isolated a single imidazolinone-resistant rice plant, using conventional breeding techniques. Seed breeders then crossed the plant, which had poor agronomic characteristics, with existing lines. The herbicide-resistant rice varieties are not the result of genetic engineering.

American Cyanamid and Louisiana State University worked out a licensing and royalty arrangement for developing the herbicide-resistant technology. The agreement is now between LSU and BASF, which purchased Cyanamid in 2000.

Formed in 1997, Horizon Ag, LLC, is a joint venture of five established seed marketing companies with locations in Arkansas, Mississippi, Louisiana and California.

A portion of the royalty from the sale of Clearfield varieties will go to the Rice Research Station for its part in supplying the germplasm and for the patent it has on the technology.

e-mail: [email protected].

Clearfield's stewardship program.


  • Growers will purchase certified Clearfield rice seed to produce a single commercial crop.
  • If the grower uses an imidazolinone herbicide, the grower agrees to use Newpath in accordance with the product label, including the stated label rate and timing.
  • In addition, growers must attend and complete a Clearfield rice grower certification seminar in order to purchase Clearfield rice seed. Violators of the Clearfield stewardship program and PVP laws will be prosecuted to the full extent of the law.


  • Avoid continuous rotation of Clearfield rice. If red rice is present at harvest, do not rotate to Clearfield Rice the following season.
  • Plant Clearfield rice early enough to avoid synchronous pollination and minimize outcrossing potential.
  • Maintain weed free levees and red rice free ditches and turn rows.
  • Rogue or wick red rice escapes.
  • Roll and flood Clearfield rice fields after harvest to promote germination of weeds in the fall.
  • If red rice is present at harvest, do not ratoon rice crop, regardless of plans to harvest or use as habitat.
  • Use alternative mode of action herbicides and cultivation where feasible, in all rotational crops.

Water management:

  • If sufficient rainfall is not received within 2 days of soil application, a flush is needed to activate Newpath.
  • Maintain good soil moisture up to permanent flood.
  • Initiate permanent flood within 2 days of postemergence application or as soon as the growth stage of rice permits.
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