Payoff for Reducing Plant Population?
Sunflower producers, particularly in the High Plains, might want to consider backing off on plant populations if dry conditions or/and insect pressure is expected to be a problem.
It’s generally understood that sunflower adjusts to lower populations by increasing seeds per head and weight per seed. The plant adjusts to higher populations by decreasing seeds per head and weight per seed.
Larry Charlet, USDA entomologist, Fargo, and JP Michaud, Kansas State University entomologist, Hays, both agree that in areas where stem-boring insects have been or may be a problem, growers should reduce plant populations to help minimize damage that such insects as stem weevils and long-horned beetle (also referred to as sunflower stem girdler, dectes or soybean stem borer) can cause. Lower plant populations and less plant competition results in larger diameter stalks that are less susceptible to breakage. Michaud suggests lowering oil sunflower populations to around 15,000 plants/acre, and confection to 14,000, in dryland fields at risk to stem insects.
Texas A&M University extension agronomist Calvin Trostle suggests an even lower plant population of about 12,000 plants per acre might be more appropriate for confection sunflower produced in the Southern Plains. Research at Texas A&M indicates that lower populations may be better in drought conditions, and result in a larger confection seed size that’s more attractive in the marketplace.
Over the last three years, Trostle and Jim Barber, Texas A&M Research & Extension Center Lubbock, evaluated different seeding rates of both confection and NuSun sunflower, varying from 12,000 to 27,000 planted seeds per acre, grown under furrow irrigation. Plant population did not have a significant effect on confection or oil sunflower yield in this trial at either location, supporting the hypothesis that seed drop can be reduced without significantly affecting yield. Confection seed size decreased at higher populations.
Trostle says the results indicate that for confection sunflower, at least in north Texas, “less can mean more,” saving on seed cost and soil moisture, while enhancing large seed development. For oil sunflower, reduced seeding rates appears to reduce seeding costs slightly, and may help reduce risk in the driest of years, but does not appear to have a large effect on yield or economic return for moderate irrigation levels.
These results may not be the same in other sunflower-growing locations, he cautions. North Texas is a different growing environment than North Dakota. And even in other areas of the High Plains, irrigated sunflower production may need more plants to reach a higher yield goal, and a drop-off in seed size might be less pronounced. “If I knew that I was going to be irrigating more, than I would shift a recommended seed rate up,” Trostle says. “We had some producers here in the Texas Panhandle last year that dropped about 28,000, even 30,000 seeds per acre on 30” rows shooting for 4,000-lb yield goal. That was probably the right decision, knowing they would probably irrigate at 15-16.”
In extreme drought, reduced plant populations will have a limited effect on yield, says Ron Meyer, Colorado State University extension agronomist. “We’ve seen dryland yields at 200 lb per acre. Reduced populations won’t help when it’s that dry. Around here, we aim for a final dryland population for oils of about 17,000 to 19,000 plants per acre. You could drop back slightly from that, maybe 10-15%, but I’m not sure we’d see a benefit dropping much more than that.”
Kansas State University extension agronomist Roger Stockton agrees there may be benefit in dropping plant population to a small degree in dry conditions, but raises a few concerns in doing so. “When you get a bigger pie-plate head on oil-type sunflower, it might be harder to keep it standing long enough to get it in the combine. That would be less of an issue with short-stature sunflower. Another drawback might be less residue cover through the winter with fewer stalks,” he says. “Around here, given our conditions, I’d probably go ahead and shoot for 18,000 plants, and then if I only got around 15,000, I probably wouldn’t be too concerned about it.”
Duane Berglund, North Dakota State University extension agronomist, says that in North Dakota, recommendations generally specify a confection plant population of about 16,000 to 18,000 plants per acre, an oil-type population of about 20,000 to 22,000 plants per acre at 30” row spacings, and a population of 22,000 to 26,000 or more for solid-seeded/narrow row oil sunflower, and oil sunflower planted in the Red River Valley.
“Up here I would worry that if we reduce populations too much, we end up with larger stalks and heads that increase dry-down time,” he says. “You could maybe drop populations by 3,000 or 4,000 under dry conditions. So in western N.D. if you’re generally planting oilseed sunflower 20,000 to 22,000, you could consider going 16,000 to 18,000.”
Berglund says a sunflower grower might also want to consider wider rows if moisture is a concern. “Row crops, including sunflower and corn, can tap into soil moisture between the rows a bit better during water stress at 30” row spacings compared to narrower rows.”
Confection sunflower growers should consult with the processor they work with for plant population recommendations that may be specified under their production contracts. – Tracy Sayler
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