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Are Your ‘Flowers Harvest Ready?

Wednesday, September 17, 2003
filed under: Harvest/Storage

Harvesting sunflower can be a balancing act: Jump the gun, and you may end up with an immature crop that doesn’t reach its full yield and oil potential, as well as higher moisture and additional seed drying expenses. Wait too long, and you risk losses from plant lodging, seed losses from shatter and bird damage, and weathering that reduces seed quality.

A study in the Dakotas measured just how damaging a delayed sunflower harvest can be.

Burton Johnson, a sunflower researcher at North Dakota State University, coordinated the plot trials which examined the influence of harvest date on sunflower performance from 1998-2000 at Carrington, Hettinger and Prosper (near Fargo) in North Dakota, as well as one at Brookings, S.D. A site near Minot, N.D., was also added.

Commercial oil hybrids in the study were Cargill 187, Interstate 6111 and Pioneer 6338, representative of early, average and late maturity, respectively. P6338, a stay-green hybrid, was included in the second and third years of the study.

For each hybrid at each test location, there were five harvest dates spaced at approximately 8 to 10 day intervals, with the first occurring when seed moisture for a hybrid reached 20 to 25%. Thus, the harvest span was 35 to 40 days from the first to last date at each test site. Yield, seed shatter, plant lodging, seed oil content, and incidence of head and stalk diseases were then analyzed for each harvest date.

There was a harvest date effect on hybrid yield for nine of the 12 environments, with yield losses ranging from 15% to 49%. “Close to 50%; that’s about half of your crop. A 33% loss would be a third of your crop. That illustrates the effect of a delayed harvest. You just can’t blink off that kind of loss,” says Johnson.

Only three times during the course of the study did harvest date have no influence on yield: at Brookings in 1998, Hettinger in 1998, and Carrington in 1999. Otherwise, about 75% of the time, there were yield losses, which varied by harvest date, and among hybrids and environments, depending on climatic conditions.

Plant lodging resulted in the greatest yield loss, followed by seed shatter that was particularly high when weather conditions promoted head disease. Yield losses were most evident at the later two harvest dates, and tended to increase when these dates were delayed. Yield loss factors became cumulative as harvest was delayed and caused significant yield reductions. Lodging was also influenced by topography, soil type, precipitation, and wind at three of the test sites.

Johnson says the study affirms that the potential for yield losses exists when pests, vulnerable weather conditions, and delays in harvest occur.

Moisture testing is key

Many producers gauge their sunflower harvest on a killing frost. But as the harvest study indicates, a frost shouldn't be the sole meter for harvesting 'flowers. Given weather conditions that can vary, along with the production of stay-green hybrids, moisture testing is key to avoid harvesting too early or too late.

“Sometimes there's a misconception that you have to have a killing frost before sunflower is ready to harvest. Certainly that is true in many years,” says Curt Stern, field representative with ADM's Northern Sun at Enderlin, N.D. “However, when we have warm conditions, the crop can reach maturity faster. Some producers will drive by the crop and judge it visually and believe it's not ready for harvest. So they wait for that killing frost and then come out and find seeds down in that four to five percent moisture range, and then they're losing seed from shelling, along with test weight.”

Drydown is quicker and less dependent on frost in more southerly sunflower growing areas, where warmer temperatures and lower humidity accelerate crop development. Stern thinks a good harvest range is 10 to 15% moisture. He points out that it can be more economical to artificially dry a crop that's close to 15% moisture, than to risk increased shelling or other problems once the standing crop falls below 10%.

“I think that's even more true with confections, because you have a much bigger, plumper seed; so the seeds don't pack as tight in the head, and the shelling potential increases compared to oil sunflower,” he adds.

“I think the message would be to get out and check the crop moisture - especially if it's a warm fall with low humidity,” Stern says. “It's as simple as running out there and rubbing a few seeds out of the head and getting a moisture test.” When testing a sample, be sure to take into account the potential moisture differences between the hull and the inside kernel. A moisture meter can be fooled by sunflower with hulls that are drier than the kernels inside. Thus, consider taking a test sample and put it in a coffee can, then leave it a few hours or overnight for a more accurate moisture reading.—Tracy Sayler

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