Lincoln, Nebraska
September 2, 2003

from CropWatch News Service
University of Nebraska Institute of Agriculture and Natural Resources Cooperative Extension

The Clearfield Production System for Wheat (CPSW) was introduced last year by its developer, BASF Corporation. This system combines the use of Beyond^TM herbicide with a winter wheat cultivar containing a gene that confers tolerance to this herbicide. This allows for selective control of winter annual grass weeds such as jointed goatgrass, downy brome, and feral rye in winter wheat.

Wheat cultivars with this gene may be treated with Beyond herbicide with minimal risk of crop injury. Beyond will seriously injure or kill winter wheat cultivars without the tolerance gene. In field research in western Nebraska and throughout the western winter wheat belt, CPSW provided excellent (95%+) control of jointed goatgrass and downy brome when weeds were treated with 4 ounces of product per acre in the fall or early spring. Fair to good (80%+) control of feral rye required an early fall application with 5 ounces of product per acre. It provided optimum control of feral rye with little wheat injury when Beyond was applied before rye plants had produced a tiller and wheat had at least three leaves emerged. Some wheat growers in the Nebraska Panhandle reported inconsistent control of feral rye with Beyond herbicide in the 2002-2003 crop. Cold weather conditions within a few days of application may help explain some of the inconsistent performance. Although feral rye control with Beyond is not at the same level as with the other winter annual grasses, it is still the best selective control method available for feral rye at this time. Each grower will have to decide for themselves as to whether 80-85% control of feral rye is worth the $20+ per acre treatment cost.

Among weed control specialists, the biggest concern with the Clearfield production system is the potential for developing herbicide-resistant weeds. Because Beyond provides such excellent control of jointed goatgrass and downy brome, it will exert a tremendous selection pressure for resistance. Beyond belongs to a class of herbicides known as ALS-inhibitors. Other herbicides in this class, such as Glean and Pursuit, have a history of quickly selecting for resistance in weed populations. Examples include ALS-resistant kochia, prickly lettuce, and pigweed. In the case of jointed goatgrass, resistance also may occur through pollen transfer. Jointed goatgrass and wheat share a common genome, the D genome, acquired from a common ancestor. Research has shown that there is a slight chance of moving the resistance gene from a Clearfield cultivar to jointed goatgrass within several generations. Without adequate safeguards, it is likely that weeds resistant to Beyond will be common in just a few years.

Among weed control specialists, the biggest concern with the Clearfield production system is the potential for developing herbicide-resistant weeds. Because Beyond provides such excellent control of jointed goatgrass and downy brome, it will exert a tremendous selection pressure for resistance. Beyond belongs to a class of herbicides known as ALS-inhibitors. Other herbicides in this class, such as Glean and Pursuit, have a history of quickly selecting for resistance in weed populations. Examples include ALS-resistant kochia, prickly lettuce, and pigweed. In the case of jointed goatgrass, resistance also may occur through pollen transfer. Jointed goatgrass and wheat share a common genome, the D genome, acquired from a common ancestor. Research has shown that there is a slight chance of moving the resistance gene from a Clearfield cultivar to jointed goatgrass within several generations. Without adequate safeguards, it is likely that weeds resistant to Beyond will be common in just a few years.

In order to delay the onset of herbicide resistance, fields treated with Beyond should not be treated with another ALS-inhibitor such as Ally or Peak. If additional weed control is needed, for example to control warm season broadleaf weeds like kochia or pigweed, use herbicides with a different mode-of-action. Herbicides containing 2,4-D or dicamba would be good choices for additional weed control.

The BASF Clearfield stewardship program for wheat requires the use of only certified seed in order to prevent the pollen flow required to produce a jointed goatgrass plant with resistance to Beyond. Growers will not be allowed to save back any grain for seed. The stewardship program also does not allow for using CPSW more than twice in a four-year period. University researchers in the Great Plains are concerned that this requirement is not adequate to sufficiently delay the onset of herbicide-resistant weeds. They recommend that the CPSW not be used more than once every three years. This would prevent growers in the winter wheat-fallow rotation from using the system every time they grow wheat.

Another concern with this system is the high cost of the herbicide. The herbicide costs about $4 per ounce or $16 per acre for a 4-ounce per acre rate.

For 2003 planting only three Clearfield cultivars will be available to Nebraska growers. These are 'Above', 'AP 401CL', and 'AP 502CL'. Above is a public variety developed at Colorado State University. It is a 'TAM 110' type with questionable winter hardiness for Nebraska. Although Above performed well in the 2003 University of Nebraska Wheat Variety Test plots, several wheat growers in western Scotts Bluff and Banner counties were disappointed with its yield performance. The reason for the poor performance in this area is not known, however it may be related to marginal adapatability of the variety to the higher elevations there. Agripro will have two Clearfield cultivars for sale. AP 401CL is a hard white wheat with the gene for tolerance to Beyond and AP 502CL is similar to Above. Dr. Stephen Baenziger, wheat breeder at the University of Nebraska-Lincoln, is expecting to have several high yielding, Nebraska-adapted cultivars for the CPSW available in fall 2005 or 2006.

The gene conferring resistance to Beyond was developed by mutagenesis, a technique that has been used in plant breeding for over 70 years. Cultivars with the gene are not considered to be genetically modified organisms (GMOs) thus market acceptability is not a concern with wheat cultivars used in this system.

Growers interested in CPSW should check with their local BASF agricultural representative or agricultural chemical dealer. Growers will be required to enter into a contractual arrangement with BASF to ensure stewardship requirements are followed. With proper management, CPSW provides winter wheat growers with a very effective weapon to gain the upper hand in the battle against jointed goatgrass, downy brome and feral rye.

Drew Lyon Extension Dryland Cropping Systems Specialist
Gail Wicks Extension Weeds Specialist