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You Are Here Sunflower Magazine > Clearfield Plus Poised to Replace Clearfield


Sunflower Magazine

Clearfield Plus Poised to Replace Clearfield
September 2012

Some in the industry point toward herbicide-tolerant sunflower technology — in the form of the Clearfield® Production System from BASF — as the savior of the crop in the mid- to late 1990s. Many growers had been giving up on sunflower due to the lack of effective weapons to combat persistent weeds.

Weeds in sunflower are a source of frustration for growers and, when severe, obviously lead to decreased yield. The advent of this technology introduced a post-emergence herbicide option that had not available on conventional sunflower. Herbicide-tolerant sunflower allowed growers to plant across a wider range of environments with greater peace of mind when it came to weed control.

The key to herbicide-tolerant sunflower technology was offering the grower more flexibility. Now, a new production system just released by BASF called Clearfield® Plus technology, will advance that valuable flexibility.

Ironically, the gene that started it all for improved weed control came from a wild sunflower, which is classified as a weed. The ImiSun trait, based on a natural muta-tion in wild sunflower, was discovered in 1996 in wild sunflower, paving the way for herbicide tolerance with the Clearfield® Production System sunflower hybrids that were first introduced in 2003. However, one key ingredient is different in this new system. The Clearfield Plus trait was not derived from wild sunflower (instead, it was selected in an elite cultivated inbred line), so it does not contain attributes asso-ciated with the plant’s wild “cousin” and the wild sunflower genetic impact on yield and oil content.

In 2000, an initiative was headed up by BASF and the Argentina-based company, Nidera, to create a more-efficient, single-gene breeding system to develop sunflower with greater herbicide tolerance, improved weed control, oil content and yield potential. By 2006, BASF began working with its global seed partners to integrate this new innovative Clearfield Plus trait into elite commercially viable hybrids. In 2010, the first commercial Clearfield Plus hybrid was launched in Argentina — and the technology will be available for U.S. growers in several locally adapted hybrids in 2013.

Kent McKay, North Dakota-based BASF technical services representative, says the new technology has big benefits for both the seed companies and the grower. “For the seed companies, it added ease of breeding of the hybrids for increased tolerance, and [it] shortened their time needed to build and bring to market the new Clearfield Plus hybrids with improved herbicide tolerance, yield and oil content potential,” McKay explains. “For the grower, it affords more flexibility in the crop stages. There’s more-consistent and better control of harder-to-control weeds. We target taking that control up 8 to 15% from the current system of 80 to 90% control on the harder-to-control broadleaf and grass weeds. Plus, the added options with adjuvants make this a great choice for growers.”

Dr. Ryan Bond, BASF Clearfield Production System Sunflower market manager, notes, “Clearfield Plus technology is the second-generation Clearfield trait that delivers enhanced herbicide tolerance for improved crop safety and performance. This innovative system equates to more-robust weed control and greater crop per-formance potential in terms of yield and oil content.”

The bottom line, says BASF, is that Clearfield Plus technology makes it easier for seed companies to breed tolerance to imidazolinone herbicides in sunflower hybrids and pass along all it has to offer for the growers. There are five important areas where the new production system offers advantages:

Breeding – Instead of multiple genes involved with the Clearfield trait, the new Clearfield Plus technology involves only a single gene inferring herbicide tolerance to Beyond® herbicide. The inherent trait in the original Clearfield sunflower is controlled by at least two or more genes; one gene is the natural acetohydroxy acid synthase (AHAS) mutation, and the other(s) are known as modifiers or enhancer (called the “E” factor). However, since there’s no diagnostic method available to determine the “E” factor, breeding selections have to rely on phenotypic or observed evaluations of plants treated with Clearfield herbicides. This makes the already lengthy breeding process even more tedious and time consuming. In contrast, Clearfield Plus technology involves only a single gene without the need for an enhancer or “E” factor, making the process easier and faster for seed breeders.

Herbicide Tolerance – Early green-house studies exposed Clearfield Plus sunflowers to up to six times the recommended rate of a Clearfield herbicide (Beyond herbicide in the U.S.). This greater herbicide tolerance affords growers more options to use more aggressive adjuvants and herbicide formations, which would provide better weed control in situations where there is either high weed pressure or difficult-to-control weeds. Essentially, greater tolerance allows the grower more use-rate flexibility when the situation or environment warrants it, with no known adverse effects on the plant.

Weed Control – Trial data from 2008-2010, shows improved grass and broadleaf weed control in Clearfield Plus fields versus Clearfield-treated fields. The study also found that adjuvants such as MSO (methylated seed oil) or BASF’s DASH® can be used on Clearfield Plus sunflower to enhance the activity of the herbicide, whereas less-aggressive adjuvants, like nonionic surfactants, are recommended for Clearfield sunflower.

Oil Content – Preliminary data have shown that oil percentages of Clearfield Plus sunflower are on par with conventional hybrids and higher oil content per acre than Clearfield sunflower. The difference may be attributed to the fact that there is no “E factor” linkage to wild sunflower in the new Clearfield Plus system.

Yield – Data in field trials have shown Clearfield Plus hybrids yielded comparable to conventional hybrids. The weed control provided by Clearfield and Clearfield Plus over pre-emergence herbicides in conventional sunflower could be an attributing factor, particularly in environments prone to weed issues. More field testing is being conducted to assess Clearfield Plus yields across variable environments to confirm these data.

Plus to Replace Clearfield


BASF and its seed partners will launch Clearfield Plus in 2013 in the U.S. Eventually, the new technology will completely replace the previous Clearfield system as seed companies continue to integrate it into their breeding programs.

Bond explains that preliminary data show that Clearfield Plus sunflower provided greater yield and oil content on a per-acre basis than Clearfield sunflower. Improved grain yield can be a direct result of improved weed control and enhanced crop tolerance of the Clearfield Plus trait.

Since 2003, seed partners have improved the performance of Clearfield hybrids in terms of average yield and oil percentage. BASF field test trials show this second-generation Clearfield Plus trait for sunflower provides greater herbicide tolerance to Beyond herbicide and higher oil content on a per-acre basis than Clearfield sunflower.

“Both Clearfield and Clearfield Plus hybrids will be available in the marketplace in 2013. The enhanced performance of Clearfield Plus is expected to expedite market adoption from Clearfield to Clearfield Plus,” Bond adds.

Seed Available in 2013


One of these seed partners, Mycogen Seeds, just last month announced the introduction of three new sunflower hybrids for the 2013 season, including a confection hybrid with the Clearfield Plus Production system. The new hybrid is billed as offering expanded weed control options.

John Kalthoff, sunflower marketing specialist with Mycogen, says, “Our Clearfield Plus introduction with one hybrid will be a quite small introduction. We hope to gain some additional understanding in the field next summer.”

Input costs associated with the new Clearfield Plus Production System for sun¬lower will be announced upon commercialization expected in 2013 by BASF and its seed partners.

— Sonia Mullally

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