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2003
Table of Contents |
Winter wheat ranks high in importance as an agricultural crop in the Pacific Northwest states of Washington, Idaho, and Oregon. These states rank 3rd, 7th, and 18th in U.S. winter wheat production with a total estimated value of production of over $633 million in 2000 (National Ag. Statistics Service). Winter wheat is a winter annual grass that is planted and emerges in the fall; overwinters as a small plant; grows fast and develops tillers in the spring; and is harvested in July and August. Winter annual grass weeds such as jointed goatgrass, downy brome, feral rye, and Italian ryegrass have the same growth cycle as winter wheat and are difficult to control in conventional wheat-fallow rotations. These weeds annually account for millions of dollars of lost wheat production and reduced quality – dockage. There has been moderate success in controlling winter annual grasses in wheat by utilizing multiple-year crop rotations with spring crops and fallow periods, and with chemical control of weeds before and after the wheat crop. However, before Beyondä herbicide in CLEARFIELD* wheat, there was no herbicide that could effectively control jointed goatgrass or feral rye in winter wheat.
The CLEARFIELD Production System for wheat is a unique system comprised of herbicide-resistant wheat varieties, Beyond herbicide to manage problematic weed species, and a stewardship agreement with growers to ensure the use of best management practices for system sustainability. The first publicly-developed CLEARFIELD winter wheat varieties to be released in the United States, ‘Above’ (from Colorado State University), 'AP502 CL' and 'AP401 CL' (marketed by AgriPro Wheat) are resistant to Beyond herbicide for use in the CLEARFIELD Production System for wheat. These two hard-red varieties and one hard white variety are best adapted to areas of the central Great Plains from western Nebraska through eastern Colorado and western Kansas and into the Texas panhandle. In the Pacific Northwest, General Mills has licensed two new CLEARFIELD winter wheat lines developed by Northwest Plant Breeders, Inc. One of these varieties has been released under the name 'CLEARFIRST'. Public and private plant breeders in the Pacific Northwest are actively developing other CLEARFIELD winter wheat varieties for Pacific Northwest production regions.
How was the CLEARFIELD
Production System for wheat developed?
BASF Corporation developed CLEARFIELD crop systems for corn, rice, canola, and
sunflower. In the late 1980s, BASF scientists used a chemical mutagen for wheat
to induce a mutation using the French wheat cultivar, ‘Fidel’, and
found a herbicide-resistant plant. Herbicide-resistant Fidel was not commercially
acceptable in the U.S.A. so BASF (then American Cyanamid) cooperated with breeders
from the Texas Agricultural Experiment Station to incorporate the herbicide
resistance into a commercially acceptable line. Crosses to transfer the herbicide
resistance to adapted wheat varieties were completed at Texas A&M University
in 1996. Populations segregating for herbicide resistance and other traits were
obtained by several universities from BASF for further testing and development.
At the same time varieties were being developed, weed scientists at Oregon State
University, University of Idaho, Washington State University, and BASF were
studying how to best use Beyond™ herbicide under Pacific Northwest conditions.
CLEARFIELD* wheat
variety development in the Pacific Northwest
Currently, the one variety released for commercial use in the PNW, CLEARFIRST
is a tan-chaffed, soft white winter wheat with a Madsen background developed
by Northwest Plant Breeders, Inc. and Dr. Calvin Konzak. It is adapted to PNW
wheat growing regions. Marketing will be done by General Mills based out of
Idaho Falls, Idaho. CLEARFIRST wheat was placed in pilot demonstrations for
the 2002-03 production season. The pilot program consists of 28 locations managed
by producers throughout Washington, Oregon, Idaho, and Utah ranging in size
from 10 acres to over 30 acres. Weeds species targeted in the pilot demonstrations
include wild oat, Italian ryegrass, feral rye, jointed goatgrass, downy brome
and volunteer cereals (including winter and spring wheat and barley). CLEARFIRST
was planted in conventional, minimum-till, and zero-tillage systems ranging
from 8-inch precipitation to over 30-inches of annual precipitation. Certified
CLEARFIRST seed is being raised on 2000+ acres in Washington and Idaho for the
2003-04 season with anticipation of 150,000 +/- acres of certified seed available
for growers across the Pacific Northwest in the fall of 2003. Public and private
plant breeders in the Pacific Northwest are actively developing other CLEARFIELD
winter wheat varieties for Pacific Northwest production regions. Release of
advanced lines from Oregon State University and the University of Idaho are
expected in 2003.
Are the CLEARFIELD
wheat varieties genetically modified organisms (GMOs)?
No foreign, non-wheat, DNA was introduced or inserted into CLEARFIELD wheat
varieties at any time during the development. CLEARFIELD wheat varieties are
thus classified as “non-GMO” in the U.S.A. and are not subject to
restrictions in either domestic or overseas markets. The induced mutagenesis
process described above is a traditional plant breeding technique and has been
used for several decades to create crop varieties (including wheat) that are
grown on large acreages in the U.S.A. and around the world.
How does the herbicide
system work in susceptible and resistant plants?
Beyond, and similar herbicides, inhibit the activity of the enzyme, acetolactate
synthase (ALS), also known as acetohydroxyacid synthase (AHAS), which is necessary
for the biosynthesis of the branched chain amino acids valine, leucine, and
isoleucine. In response to a Beyond herbicide application, ALS is inhibited
in susceptible plants depriving them of the previously mentioned, essential
amino acids. This causes the eventual death of treated plants. The ALS enzyme
is unique to bacterial and plant species and is not found in the animal kingdom.
Mutation gave rise to an altered form of the ALS enzyme that is not affected
by the herbicide at normal application rates. Beyond herbicide received EPA
Federal registration for use in CLEARFIELD wheat in December 2001.
What weed species
does Beyond control?
Beyond is a broad-spectrum herbicide (grass and broadleaf weeds) that provides
post-emergence and some in-season residual weed control. Grasses controlled
by Beyond include jointed goatgrass, feral rye, downy brome, Italian ryegrass,
wild oat, and volunteer cereals. In field studies with Beyondä, feral rye
and Italian ryegrass were more difficult to control than jointed goatgrass,
indicating that a properly timed application at full rate is necessary to optimize
control of these two weeds. Beyond also controls several winter annual broadleaf
weeds including flixweed, henbit, chickweed, shepherd's purse, field pennycress,
and other mustard species. Spring applications of Beyond will control or suppress
summer annual broadleaf weeds such as common lambsquarters, pigweed, and wild
buckwheat.
CLEARFIELD Stewardship
Stewardship of the CLEARFIELD* production system is important to prolong its
longevity for future generations of Pacific Northwest wheat producers. Sustaining
the life of this technology is also in the public interest. With the Pacific
Northwest wheat crop worth an estimated $633 million annually, the loss of production
due to winter annual grasses and dockage could account for 10 percent, or $63
million dollars, in a single year. The biggest threat to prolonging the life
of CLEARFIELD technology is developing herbicide-resistant weed biotypes. This
could happen by either selecting for resistance among naturally occurring weed
biotypes or, in the case of jointed goatgrass, direct transfer of the CLEARFIELD
resistance trait through natural outcrossing. Because wheat and jointed goatgrass
are genetically related, and the herbicide tolerance gene is found on a set
of chromosomes common to both wheat and jointed goatgrass, outcrossing from
wheat to jointed goatgrass can occur and has been documented under Pacific Northwest
conditions (Zemetra et al. 1998). Unsuccessful stewardship might lead to the
emergence of a wheat-jointed goatgrass hybrid that (when backcrossed naturally
to jointed goatgrass) would give rise to a jointed goatgrass population resistant
to Beyond and related herbicides. The following information outlines the stewardship
program developed by BASF, and our comments to expand on the BASF program. Please
note that mention of the CLEARFIELD program, Beyond herbicide, or the discussion
of these products do not constitute our endorsement or recommendation for use.
BASF Stewardship
Requirements
According to BASF, growers must purchase certified CLEARFIELD wheat seed every
year from a CLEARFIELD seed retailer. This means that saving seed to plant next
year’s crop will not be allowed (NO “brown-bagging” or “bin-running”).
Seed increase fields (Foundation, Registered, and Certified) are grown following
strict guidelines that ensure that fields are free of noxious weeds and “off-type”
wheat. The use of registered or certified seed ensures proper herbicide tolerance
to Beyond and prevents contamination from a non-CLEARFIELD variety. The penalty
for planting CLEARFIELD wheat saved seed could be $100/acre or more. Proof-of-purchase
records for CLEARFIELD wheat seed and Beyond herbicide must be provided to BASF
prior to servicing of any claim. The stewardship requirements and recommendations
(common sense good stewardship practices) were developed to prolong the life
of CLEARFIELD technology in the field. Northwest wheat producers need to study
these carefully before signing a CLEARFIELD stewardship grower agreement with
BASF prior to, or at the time of seed purchase. Growers who use Beyond herbicide
agree to use it in accordance with the product label, including stated label
rates and timing.
BASF Stewardship
Recommendations
Avoid continuous use of CLEARFIELD wheat on the same land. This reduces the
reliance on Beyond in selection of herbicide resistant weed biotypes and promotes
crop rotation and use of alternate control methods. Utilize crop rotation .
Rotation of CLEARFIELD* winter wheat with spring crops breaks the cycle of winter
annual weeds and allows the use of alternate mode-of-action herbicides. Use
herbicides with different modes-of-action. Limit the sole reliance of ALS-inhibiting
herbicides no more than 2 out of 4 years unless other control practices are
implemented on target weeds (this recommendation will be discussed, further).
Where needed to achieve broad spectrum control of multiple weed species, use
sequential applications or tank mix herbicides with multiple modes-of-action
on target weed species. This strategy should span across crops and years to
provide sound weed resistance management. Properly manage weeds in wheat-fallow-wheat
rotations. In the fallow year, control weeds (especially winter annuals) before
they set seed with burndown (non-ALS) herbicides or tillage. Specific recommendations
for jointed goatgrass include treating the entire CLEARFIELD wheat field with
a labeled rate of Beyond™ herbicide. The labeled rate of Beyond will provide
a high level of jointed goatgrass control and reduce the chance of outcrossing.
Control jointed goatgrass in fence rows, road ditches, and pastures around CLEARFIELD
wheat fields before jointed goatgrass seed set to further reduce the chance
of outcrossing.
Additional Points
About Stewardship
The development of herbicide resistant grass weeds such as jointed goatgrass,
downy brome, and others is a very real possibility with over-reliance on CLEARFIELD
wheat and Beyond herbicide. As previously mentioned, Beyond herbicide belongs
to a herbicide class known as ALS inhibitors. Use of this class of herbicide
has produced a dramatic array of herbicide resistant weeds since about 1982
when the first ALS resistant weeds were identified (Figure 1). There are currently
73 weed species identified, world-wide, that are resistant to ALS inhibitor
herbicides (Heap 2002), including such common Pacific Northwest weeds as kochia,
Russian thistle, prickly lettuce, and downy brome.
To determine how rapidly herbicide resistance might occur with Beyond herbicide in CLEARFIELD wheat, historical observations from other weed species can be used as an indication. As an example, continuous use of GleanÒ herbicide (an ALS inhibitor) in wheat resulted in the development of herbicide-resistant kochia and prickly lettuce 5 years after the introduction its commercial introduction (Thompson et al. 1994). Continuous use of BeaconÒ (another ALS inhibitor) in Kentucky bluegrass seed production resulted in herbicide-resistant downy brome after 4 years of continuous use (Mallory-Smith et al. 1999, Ball and Mallory-Smith 2000).
To estimate the impact of cropping practices and Beyond herbicide use on ALS inhibitor resistance development in jointed goatgrass, we independently constructed two separate simulation models to predict the rate of Beyond resistance development in jointed goatgrass. Both predictive models are based on known information about crop management impacts on jointed goatgrass populations, information on the effectiveness of Beyond herbicide for control of jointed goatgrass, and knowledge of natural mortality factors in the field (Hanson et al. 2002, Rainbolt and Thill, unpublished data). Estimated changes in jointed goatgrass seed numbers in the soil over a 10 to 15 year period were calculated by the simulation models based on scenarios where BeyondÔ herbicide were used every year, or once in two, three, or four years.
Figure 1. World-wide occurrence of herbicide resistant weed biotypes by herbicide class.
In the model developed at Oregon State University (Hanson et al. 2002), numbers of Beyond resistant jointed goatgrass individuals increased and surpassed susceptible jointed goatgrass numbers after 4 years when used each year in a continuous, CLEARFIELD* winter wheat system (Figure 2A). In a winter wheat – fallow crop rotation, resistant jointed goatgrass numbers surpassed susceptible numbers after 9 years if CLEARFIELD wheat and Beyond herbicide were used every crop year (Figure 2B). This scenario is within the BASF guidelines that allow CLEARFIELD wheat to be used every 2 out of 4 years. In a simulation of a winter wheat – fallow crop rotation with CLEARFIELD wheat grown every other crop (once in four years), a Beyond resistant population did not surpass the susceptible population during the 10 year simulation (data not shown). These results are similar to those obtained from a life-table model constructed by University of Idaho researchers (Rainbolt and Thill, personal communication). In their predictive model, developed independently from the O.S.U. model, a Beyond resistant jointed goatgrass population surpassed the susceptible jointed goatgrass population in 4 years, if CLEARFIELD wheat was grown and sprayed every year. In simulations of CLEARFIELD use 1 year out of 2, resistant jointed goatgrass populations surpassed the susceptible population after 10 years. In simulations of CLEARFIELD use 1 year out of 3, the resistant population surpassed the susceptible after 14 years, and it did not develop if CLEARFIELD wheat was grown and sprayed 1 year out of 4 (data not shown). Based on these simulation results, and from knowledge of prior cases of ALS inhibitor resistance, we recommend that the use of CLEARFIELD wheat should be limited to at least one year out of 3 to prevent the development of Beyond resistant weeds including jointed goatgrass.
In the intermediate, transitional rainfall areas of eastern Washington, a very common crop rotation consists of winter wheat – spring barley (or spring wheat) – fallow. In higher rainfall areas of the Pacific Northwest, a more intensive crop rotation of winter wheat – spring barley (or spring wheat) – legume (or Brassica) is common. With these types of crop rotations, we are less concerned about developing an ALS inhibitor resistant jointed goatgrass population, because winter wheat is grown only once every third year. Our major concern for the development of Beyond resistant weeds is in dry areas where winter wheat – fallow is the standard cropping practice. In these systems, it is desirable to attempt diversification in crop rotations, and/or limit use of CLEARFIELD* wheat to once every other crop (1 year out of 4).
Figure 2. Simulated response of BeyondÔ susceptible and resistant jointed goatgrass populations in A) continuous CLEARFIELD winter wheat, and B) winter wheat – fallow crop rotation with CLEARFIELD wheat grown every crop year (2 years out of 4). (Hanson et al. 2002).
BASF's CLEARFIELD
Stewardship Grower Agreement
Wheat producers who desire to plant CLEARFIELD wheat varieties are required
to sign an agreement with BASF stating they will adhere to the stewardship requirements.
Signing this agreement is coordinated by the seed dealer at the point of sale.
The wheat producer acknowledges that CLEARFIELD wheat technologies are protected
under U.S. patent law, CLEARFIELD wheat varieties are PVPA protected, and crops
grown from protected CLEARFIELD varieties may only be sold in normal commercial
channels for wheat and not saved or sold for use as seed. Seed producers will
obtain the signed agreements and forward the seed purchase information to BASF
who maintains a CLEARFIELD wheat technology database. The database matches grower
seed and herbicide purchases.
What will be the
label rate and cost of Beyond?
The label rate will be 4 to 6 oz/acre and 5 oz will cost approximately $20/acre.
Growers should check with their local ag chemical retailer for specific Beyond
pricing.
What will CLEARFIELD
wheat seed cost?
Seed cost is not fixed for any varieties of certified seed so the cost of seed
will depend on the demand for the seed plus possible royalties from the variety
owner. A technology fee will not be levied on the price of CLEARFIELD wheat
seed by BASF.
CLEARFIELD* Wheat Resources on the World Wide Web: www.clearfieldsystem.com
BASF Corporation Web site developed solely for CLEARFIELD crop production systems. www.jointedgoatgrass.org
Web site for the National Jointed Goatgrass Initiative covering jointed goatgrass biology, distribution, control, and genetics.
The UNIQUE CLEARFIELD SYMBOL
and CLEARFIELD® are trademarks of BASF.
Beyond is a trademark and CLEARFIELD is a registered trademark of BASF Corporation.
©2002 All Rights Reserved.
Always read and follow label directions.
Acknowledgements:
Some text used in this article was adapted from Colorado State University Crop
Production Series no. 3.116, CLEARFIELD Wheat, by J. Johnson, S. Haley, and
P. Westra. The authors acknowledge these individuals for the written material
used to produce this manuscript. The authors would also like to thank BASF for
providing information on their stewardship program, the grower agreement, and
CLEARFIELD wheat varietal information.
Literature Cited:
Ball, D. A. and C. Mallory-Smith. 2000. Sulfonylurea herbicide resistance in downy brome. Proceedings West. Soc. Weed Sci. 53:41-42.
Hanson, D. E., D. A. Ball, and C. A. Mallory-Smith. 2002. Herbicide resistance in jointed goatgrass (Aegilops cylindrica): simulated responses to agronomic practices. Weed Technol. 16: 156-163.
Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Internet. October 30, 2002. Available at: www.weedscience.com
Mallory-Smith, C., P. Hendrickson, and G. Mueller-Warrant. 1999. Cross-resistance of primisulfuron-resistant downy brome to sulfosulfuron. Weed Sci. 47:256-257.
Mallory-Smith, C., D. C. Thill, and M. J. Dial. 1990. Identification of sulfonylurea herbicide-resistant prickly lettuce. Weed Technol. 4:163-168.
Thompson, C. R., D. C. Thill, C. Mallory-Smith, and B. Shafii. 1994. Characterization of chlorsulfuron resistant and susceptible kochia. Weed Technol. 8:470-476.
Zemetra, R., J. Hansen, and C. A. Mallory-Smith. 1998. Potential for gene transfer between wheat and jointed goatgrass. Weed Sci. 46:313-317.
 Contact
us: Hans Kok, (208)885-5971
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