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Will the Crop Pull Through?

Wednesday, September 15, 2004
filed under: Harvest/Storage

Frost in June, jackets in July, August high temps in the 40s and 50s that had confused Canadian snow geese wondering whether to head south early – needless to say, there was no talk of global warming in the Northern Plains this summer.

What there is plenty talk about, however, is whether sunflower and other late-season crops will be able to make it to harvest.

“Overall you look at the corn, beans, and sunflowers out there and you see a great crop that’s coming, if you could forget about the calendar, and we can’t,” says Bruce Due, a Mycogen Seed district agronomist. “With sunflower, we’re about three weeks behind last year and about two weeks behind normal. I think the best scenario for sunflower is a later crop that may need more drying, and the worst scenario for some might be that it doesn’t finish. With corn, there’s a lot out there I just don’t think will be able to make it anymore. We could have a ton of silage.”

Mike Hagen, sunflower product manager with Interstate Seed, says sunflowers should have an advantage over corn and soybeans, since ‘flowers mature a little over a month after flowering and that sunflowers can withstand light frost better than corn and beans. Last year, some growers were already harvesting sunflower a few weeks into September. This year, some fields might even be blooming into September. “We need a long fall,” says Hagen. “We need it to stay frost-free into October, if the weather keeps up like this.”

As a rule of thumb, it’s best to see sunflower blooming in the Northern Plains by mid August, as was the case in many areas last year, says Curt Stern, field representative with ADM's Northern Sun at Enderlin, N.D. “I’m impressed with how much sunflower is blooming in August, despite the cold weather.” He points to the N.D. Ag Statistics Service August 8 crop progress report which indicated that the percentage of the state’s sunflower crop jumped to 36% blooming from 8% bloom the previous week, when highs in the 50s were predominant in much of North Dakota. Last year, 65% of the state’s sunflower crop was blooming by August 8, and the five-year average is 60%.

“We just need to get back to more seasonal temperatures to keep this crop moving,” he says. “It might be late, but it wouldn’t be the first time, and most growers are seasoned vets who know how to handle a later crop.”

Stern says it’s too early to predict how the late season might affect crop quality – a photo finish in September might help test weight, but sunflower fields struggling to mature might find it hard to pack on oil. “We’ll have a much better picture going into early October.” If the oil of this year’s sunflower crop does come in on the lighter side, Stern expects the same industry market standards to apply – a price premium for oil higher than 40%, and anything lower than that subject to discounts.

Sunflower is slightly behind average development in eastern Colorado and western Kansas, but with a longer growing season, there’s little concern in the High Plains about sunflower not reaching maturity, with the exception perhaps of late double-cropping situations, says Ron Meyer, Colorado State University extension agronomist. “Actually, with better moisture we’re in much better shape so far than we’ve been the past few years,” says Meyer. Lynn Hoelting, general manager of Mueller Grain, Goodland, Kans., agrees. “Dryland sunflower that was running around 500 lb/acre last year will be closer to 1,500 lbs this year,” he says.

Estimating maturity

North Dakota State University extension agronomist Duane Berglund points out reports of frost damage in western N.D. around June 18 that killed some winter wheat and damaged some sunflower. “I’ve never heard of frost damage the third week of June before,” he says. “The sunflower was about 8 to 10 inches tall, and the frost hurt the terminal buds, resulting in branching.”

He notes that it might not be unusual to see some sunflower fields not reach expected plant height. “You might see sunflower three-fourths of the normal height size, mainly shortened space between stalk internodes.” Berglund says cool temperatures should not affect head size, which is controlled more by hybrid genetics and plant population.

Sunflower is highly susceptible to frost at the bud and pollination stages (R5) of development. Temperatures of 30 degrees F or less can cause damage to the anthers and stigmas of the pollinating disk flowers. Unopened buds are less susceptible to frost than opened flower heads. The result of frost in the flowering period can be circular bands of undeveloped seed that would vary with individual flower heads, from banding around the outside edge to a spot in the center.

The sunflower plant is generally recognized as physiologically mature when the back of the head has turned from green to yellow (may not be the case with “stay green” hybrids) and the bracts are turning brown (Stage R-9), about 30 to 45 days after bloom, and seed moisture is around 33-35%.

A grower with stay-green hybrids will need to monitor seed moisture content, taking seed samples and testing for moisture percentage probably earlier than he otherwise would with a standard hybrid.

Another way to help indicate if physiological maturity has occurred is to rub the chaffy material on the front of a sunflower head. If it rubs off easily, the plant is physiologically mature.

Once pollination is completed and 10-14 days after petal drying occurs, the sunflower plants can withstand frost temperatures as low as 25 degrees F and have only minor damage. If hard frosts do occur, then many times only the seed in the center of the head (the last to pollinate) will be affected. Temperatures below 25 F would for all practical purposes be a killing frost.

“It takes about 46 to 48 days to go from R 5.1, about when the head opens and it starts to pollinate, to physiological maturity,” says Berglund. “We need to get our ‘flowers through pollinating and two weeks beyond that, we should be safe from frost.”

Berglund says growers can get an estimation of accumulated growing degree days or growth stages for a given date range at the North Dakota Agricultural Weather Network, online at Click the link “applications” then “sunflower.”

If late-season crops are damaged by an early frost before reaching maturity, producers who carry crop insurance must notify their insurance provider within 72 hours after they discover any damage, to ensure impending claims are settled within the confines of their insurance policies, says Gaby Kelly, risk management specialist with the USDA Risk Management Agency, Billings, Mont.

Kelly says Quality adjustment and Reduction in Value details are published in the Special Provisions of Insurance for each county and crop. Growers should visit with their crop insurance agent to determine which provisions may apply to them. – Tracy Sayler

Check average frost dates online

ND Ag Statistics Service (see page 7)

SD Ag Statistics Service

MN Ag Statistics Service

(click on general information, then scroll down to median frost dates)

Frost Affect on Late-Season Crops


Most susceptible at bud and flowering stage. Temperatures of 28 F and 30 F can result in damaged buds and sterile sections or rings in the flowering head. After pollination and petal drop, sunflower can withstand temperatures as low as 25 F with only minor damage. Twenty-five degree temperatures at the bud stage will often damage leaf and stalk below the bud and seeds will not develop.


Easily damaged by light frosts in 28-32F range. Beans that are still green and soft will shrivel. Stems rapidly turn dark green to brown and will not recover. Beans in pods that have turned yellow will mature normally. Some beans will turn yellow after 30-40 days of storage.

Pinto and navy beans

Very sensitive to frost (30-32 F range). Earlier pods with yellow to brown color are sufficiently mature to escape damage. Late green pods or flowers are easily damaged by frost. Green beans will shrivel but should be left in field until dry in order to separate from mature beans.


Usually damaged by temperatures in the 28 F range or less. Corn is usually physiologically mature 50-55 days after the 50% silking date. Colder temperatures will kill entire stalk. If only leaves above ear are frosted kernel development will continue. If entire stalk and leaves are frozen, kernel filling will cease and soft shriveled corn will result. If corn is at around 35% moisture or if black layer has formed at base of kernel, the plant is physiologically mature and kernels will develop normally despite frost. Frosted immature corn is best used for silage or fodder.

– Duane Berglund, NDSU extension agronomist

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