Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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May 20, 2013






Most of the early-planted corn appears to be emerging well, but I am hearing scattered reports of stands that are less than hoped for.  Issues are:


1.    Corn planted several days before the ground cooled experiencing “cork-screwing” as it attempts to emerge,

2.    Corn planted just before the ground cooled experienced “imbibitional chilling” (absorbing cold water), causing the seed to swell but have little germination, and

3.    Pythium seedling rots promoted by cool, wet soils.


So far I have yet to hear of a field where losses are great enough to warrant re-planting.  See Roger Elmore’s (Extension Corn Production Specialist) article at for guidance.



Corn yet to be planted


We made tremendous planting progress last week.  However, there is some corn yet to be planted.  As a reminder, a general rule is that if planting is delayed until May 25, you should select a hybrid that matures five days earlier than an adapted full-season hybrid for that area. If planting is delayed another seven days, select a hybrid that matures another five days earlier than the previous one. In general, the date to switch maturities is later in southern Iowa.


Black Cutworms


Black cutworms do not overwinter in Iowa.  Rather, moths fly in from the south and lay eggs.  There have been a few significant moth flights and cutting may soon begin.  Significant moth flights are quite common but there are infrequently problems with cutting, so a significant moth flight does not mean there will be much cutting.   There is a network of black cutworm moth traps across the state, and with the knowledge of when significant flights occur and by using daily temperatures to calculate Growing Degree Days Base 51 since the flight, we can predict fairly closely when cutting may begin, if indeed it does.  Information can be found at and





With the recent/current rains and the forecast for more to come this week, some are asking the question, "How long can crops be under water and survive?"  Emerged 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.  I have seen survival for considerably longer periods of submersion, however.  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.  Flooding can lead to greater disease problems on all crops, so be sure to dig a few seedlings up and determine if the roots have the normal white color.


A light rain shortly after the water recedes / drains might be beneficial to wash off any mud on plants.


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.  A University of Illinois study of relative emergence of soybeans planted at different depths found :


Planting Depth

Relative Emergence (per cent of the best)

0.75 inch


1.0 inch


1.5 inches


2.5 inches






June 26, 2013, 1:00 p.m.

ISU NE Research & Demonstration Farm Spring Field Day – Nashua

As details become available, they will be posted at


June 27, 2013

Special Session for Certified Crop Advisors (9:00 a.m.) &

ISU SE Research & Demonstration Farm Spring Field Day (1:00 p.m.) - Crawfordsville

As details become available, they will be posted at





If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: May 20, 2013
Contact: Virgil Schmitt

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