Late Corn Replanting Carries Major Risks

It may look good on paper with $7 per bushel corn, but don't expect good yields—and an early frost would be disaster.

With corn prices at record highs, many farmers in Iowa replanted flood-damaged fields to corn this past week. Some replanted their drowned-out areas, others replanted entire fields. As of June 27, a few farmers were still considering replanting to corn as soon as their fields dry up enough to plant.

Other farmers planted soybeans in those fields - if they could. Replanting to beans isn't an option for everyone, as a previously applied corn herbicide such as atrazine prohibits going with soybeans as a replant crop.

This replanted corn runs high risk of frost

Years of data advise caution regarding the decision to go ahead and replant corn after about June 20. Recent yield simulations run by the Department of Agronomy at Iowa State University show that while the economics may work out in a perfect situation, replanting that late in June carries with it some major risks.

"Corn planted this late has an early frost damage risk of around 40% in the southern part of the state and as high as 66% in the northern areas," says Roger Elmore, ISU Extension corn agronomist. "An early frost could mean the difference between 130 bushels an acre and 24."

Even the early season hybrids are risky

Simulations of yield potential for corn acres planted by July 1 in Iowa show early season hybrids will be the only reasonable option for anyone who finds it economical, and worth the frost risk, to replant. But planting the early season hybrids creates an additional risk since these varieties are less suited to Iowa's environmental stresses and disease.

If the weather is perfectly suited to growing corn from planting until harvest and the land is replanted by July 1, it may be possible to reach yields of 100 to 130 bushels an acre. But grain moisture content could be as high as 37% which means yet another additional cost to dry down the harvest. Complete details of the simulation can be found at:

Given the high prices of other commodities besides corn, farmers should also consider the benefits of planting soybeans, grain sorghum, various spring and summer annual forage crops, or even leaving the land fallow, says Elmore.

"The yield potential for corn drops off precipitously every day planting is delayed," says Elmore. "Our research shows a daily drop off in yield of 2.5%. And if you can't plant before July 1, corn isn't really an option."

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