The Progress of Clearfield Sunflower
There’s a lingering perception that Clearfield hybrids have a ‘yield drag’ compared to hybrids without the herbicide tolerance genetics. While Clearfield hybrid performance will vary by hybrid, by company, and by growing area, the technology today is generally on par with the genetic yield potential of non Clearfield hybrids.
Seeds 2000 sunflower breeder Pat Duhigg says that Clearfield genetics have evolved significantly since the herbicide resistance was first identified in a wild sunflower species (Helianthus annuus) accession that Kansas State University weed physiologist Kassim Al-Khatib collected from a soybean field in 1996.
Duhigg says the parent genes in the early going were closely related, and crossing them “was like first cousins getting married.” Now, 10 years later, the genetic background is much more diverse, with more hybrid vigor or ‘kick’ in the genetics compared to the early parentage.
Vince Ulstad, technical services representative for BASF, says there might also have been a tendency at first to incorporate the yet unproven technology in ‘middle of the road’ hybrids. “The question for a breeder at first might have been, ‘what and how much of my breeding nursery should I convert over to this new trait? Certainly they would not want to start incorporating the trait in poor material, but perhaps not their most elite lines either. So there would have been noticeable differences early on, but now, breeders are placing Clearfield into their best genetic material. It’s an issue that’s really a non-issue now.”
One must also keep in mind the old agronomy rule which states that “yield can rise no further than its limiting factor(s).” That is, genetic yield potential is a moot point if other factors inhibit that genetic yield potential from happening, like weeds in sunflower. So while a Clearfield hybrid might have a genetic yield potential that’s 100 lbs less than your favorite non Clearfield hybrid, the Clearfield hybrid in actual field conditions might yield 500 lbs more, with better weed control.
Clearfield sunflower with Beyond (imazamox) herbicide allows post-emerge control of key problem weeds like marshelder and cocklebur in sunflower. Clearfield/Beyond provides contact and residual activity on a number of other grasses and broadleaf weeds as well, including nightshade, pigweed, foxtail species, wild oats, volunteer cereals, puncturevine, and non-Clearfield wild or volunteer sunflower.
Growers who produce Clearfield sunflower need to be astute in managing it. Watch for skips in spraying that might miss wild sunflower, and wilds in the field perimeters. Make plans to spray a non IMI herbicide for weed control in fields and field perimeters where cross pollination amongst Clearfield sunflower and wild sunflower may have occurred.
Use alternate mode-of-action herbicides and rotate Clearfield sunflower with other non-Clearfield crops. Limit the sole reliance on ALS herbicides to no more than two out of four years in the same field. Beyond is a member of the herbicide family of AHAS or ALS inhibitors. Where applicable, use sequential or tank-mix partner herbicides with multiple modes-of-action on target weed species in the sunflower crop and in rotational crops.
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