Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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May 30, 2008



With the recent/current rains and related flooding, many are asking the question, "How long can crops be under water and survive?"  Corn and soybeans can normally only survive complete submersion for 2 to 3 days (80 day air temperature) and most forages can survive for 1 - 2 days.  The cooler the air temperature, the longer the plants can survive.  Plants NOT totally submerged will survive considerably longer.  By the time the water has receded and the field dries out, it will be easy to see whether the crop has survived or not. A light rain shortly after the water recedes might be beneficial to wash off the mud on plants. Flooding can lead to greater disease problems on all crops.

Some low-lying fields have had new depositions of soil on top of planted ground.  Corn and soybeans that had emerged will be lost.  Corn and soybeans that had not yet emerged can still come up from greater depths, especially corn.  The limit from which corn can emerge is depths of 4 – 5 inches.  Soybean, because the plant must push the seed up to the surface, is less capable of emerging from greater depths.




Time to Switch to Shorter Season Hybrids


There is still some corn to be planted in the area and the recent rain will mean further delays. It’s usually best to switch to hybrids about 5 days earlier in maturity than a full season hybrid when planting is delayed beyond May 25. If planting is delayed another seven to ten days beyond that, select a hybrid that matures another five days earlier than the previous one. It would take stands of down around 20-22,000 to justify re-planting now, assuming the remaining stand is fairly uniform. We can stick with full season soybean varieties for another month yet.







            Certified Crop Advisors can obtain 5 hours of credit (including 2 hours of soil and water) by attending a special session in the morning followed by a controlled drainage field day and the afternoon field tour at the ISU SE Iowa Research & Demonstration Farm near Crawfordsville on June 26. Other topics will include 1) Corn Yields – How High Can They Go? by Kendall Lamkey; 2) Corn Herbicide Management & Mismanagement by Jim Fawcett; 3) Does Tiling Pay? by Matt Helmers. Registration information will be posted soon.



If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: May 30, 2008
Contact: Jim Fawcett

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