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Improving Plant Stands

Sunday, January 15, 2006
filed under: Optimizing Plant Development/Yields

The 2005 U.S. Sunflower Survey observed some hard to manage yield-limiting factors (like drought) yet others that would seem to be more manageable, such as plant population. This was a factor observed to handicap yield potential in five of the six sunflower-producing states that were surveyed, most notably in Texas. Plant population was a yield limiting factor in three of the four sunflower fields surveyed in the Lone Star state.

Texas A&M University extension agronomist Calvin Trostle, Lubbock, surveyed the sunflower fields in Texas. Trostle notes that in all three of the National Sunflower Association sponsored sunflower surveys he’s taken part, less-than-optimum plant populations and plant stands have been an issue for sunflower fields in Texas. Part of it might be poor planter calibration, or using the wrong planter plate. If a planter isn’t calibrated correctly, variances in per-pound seed count, seed shape, and seed type can put plant populations off kilter, and result in uneven stands.

Sunflower plants have tremendous ability to adjust to lower populations by increasing seeds per head and weight per seed. Conversely, the plant adjusts to higher populations by decreasing seeds per head and weight per seed. Consequently, yield can be affected if population is too high, too low, or uneven.

“There are incidences of 8 to 9,000 plants per acre irrigated sunflower still yielding 2,000 lbs,” says Trostle, “but the plants can only compensate so much at lower populations.” The importance of a uniform plant stand matters for subsequent management in the growing season, including irrigation and pest control. “Treatment timing for sunflower head moth is important here,” he says. “We need uniform heads for spraying, and too many of us spray too late for optimal control.”

Trostle believes another factor that leads to poor plant populations and plant stands is planting into dry soils. “The seed needs adequate moisture to break out of that woody shell, and the seedling root needs moisture, otherwise it will struggle or might not come up.” That’s where management comes into play and where yield is impacted, even before plants pop out of the ground. In the dry conditions of the High Plains, sunflower growers who irrigate may need to prewater, so the soil profile has enough water to get the sunflower crop started off right.

Planting into moisture also means watching planting depth. Plant too shallow, and seed may not germinate, or seedlings may shrivel up if conditions are dry. Plant too deep, however, and emergence may be impacted, especially for smaller seed sizes. Sunflower should generally be planted at a depth of 1.5 to 2.5 inches, guided by soil moisture conditions.

It should be noted too that other factors can affect plant population as well, such as frost, drown-outs, downy mildew, and early-season insects. Seed treatments would help provide protection against the latter two problems. With seed treatment use becoming more commonplace in sunflower, overall plant populations and stands would generally be expected to improve – future sunflower surveys may bear this trend out.

See more information on optimizing plant populations and yields online at In the menu at left, click on ‘Sunflower Magazine’ then ‘View Archives’ and then ‘Optimizing Plant Development/Yields.’ See the article “Payoff for Reducing Plant Population?” in which Trostle and others discuss the issue of plant population.

2005 sun survey results

The 2005 Sunflower Survey, funded by the NSA, was conducted preharvest, examining 146 fields (ND 85, SD 31, KS 11, MN 8, CO 7, TX 4). In each of these leading sunflower-producing states, one field was surveyed for every 10,000 acres of production, in counties with at least 20,000 acres of sunflower production. The fields were surveyed with standardized protocol by crop survey teams in each of the states, consisting of university personnel and others in the sunflower industry.

North Dakota State University extension agronomist Duane Berglund served as project leader, coordinating the survey results. Berglund says the survey indicates how practices and pest problems can vary amongst the sunflower production region. For instance, take tillage, which in Minnesota was virtually all conventional in the fields surveyed, but virtually all no-till just across the border in South Dakota.

The survey indicated generally minimal pest damage, with disease, bird, insect, and weed problems that varied by state. Complete survey results from 2005 and previous years can be found online at Click on the ‘Growers’ link, then ‘USA Sunflower Survey.’ – Tracy Sayler

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