A September 15 frost hit some northern Iowa fields, causing damage to corn and soybean fields alike, especially fields that were already experiencing some type of stress. Yield reductions caused by the frost will depend on the maturity of the crop but across-the-board damage does not seem significant, according to ISU Extension corn agronomist Roger Elmore. He reminds producers that frost-damaged crops will have changes in drydown rate and test weights
Hear Elmore's comments on the mid-September frost by listening to this week's Crop Minute. Read more about determining frost damage and proper handling and storage of frost damaged crops in the ISU Extension publication Frost Damage to Corn and Soybeans.
Iowa crop conditions have changed a lot in the past two weeks
Crop conditions have changed a lot in the last two weeks in Iowa. "We had a killing frost, or maybe we should call it 'nearly a killing frost,' on September 15," says Paul Kassel, ISU Extension field agrnomist in northwest Iowa. "Most of the corn and soybeans did not receive any major damage from that frost event. However, about a third of the soybean crop was fairly green and likely did suffer some yield damage."
It is always difficult to assess soybean yield damage from frost, "but the top three to four leaves were mostly frosted with this September 15 frost," says Kassel. "The stems did not appear to be damaged. Also contributing to the yield loss was the cool weather that followed. It appears as though the late planted soybeans went from green-to-brown-to-yellow in about a week's time."
There has been some harvest of corn and soybeans in Iowa. A few fields of early planted soybeans have been harvested. Also there has been some corn harvested – although most of that was for silage or ear corn silage.
Some farmers already harvesting corn that was blown down by wind
"Some farmers have started to harvest the corn that was blown down in the August 23 windstorm that struck here in some parts of northwest Iowa," says Kassel. "The concern is that the severely lodged corn will really be difficult to harvest if we get an extended period of rainy weather. Rainy weather for any period of time may lead to further stalk rot and ear rot because some of the stalks and ears are lying flat on the ground."
A couple of fields that Kassel checked showed that about 30% of the stalks in these severely lodged fields may not make it into the combine. "I hope I am wrong, but the fields I checked showed that about 30% of the stalks were lying flat on the ground," he says. "Of course, this varies from field to field, but you can see the potential problem with harvest in these fields."
With high corn prices, it pays to harvest corn early to avoid yield loss
What about harvesting corn early and drying it artificially in the bin? Drying grain costs some money, but you can't take the chance of leaving corn stand in the field too long to dry. With stalk rot and other stresses weakening stalks in many fields this year, you don't want to leave corn standing too long because it runs the risk of falling down. And with today's high corn prices, those yield losses can add up to big money losses pretty quick.Grain drying costs about $7.50 to $10.00 per acre per point of moisture removed, notes Kassel. Therefore, a person can weigh the drying expense against the potential for field losses. If you save 10 bushels of corn an acre (approximately $70.00 per acre) by harvesting early, the added drying expense of harvesting at 25% moisture versus 20% moisture (approximately $50.00 an acre added expense) may work out in your favor. "This will not be an easy decision, but at least this gives a person some things to consider," he adds.