Extension Communications
Extension 4-H Youth Building
Ames, Iowa 50011-3630
(515) 294-9915
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Extension Communications |
5/25/04
Contacts:
Palle Pedersen, Agronomy, (515) 294-9905, palle@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Issues to Consider in Replanting Corn After Flooding
By Palle Pedersen
Extension Agronomist
Iowa State University
Corn that currently is not underwater is stressed and yellow because of the cool temperatures and wet, saturated soils. Farmers need to make stand evaluations and assessments in each field. Based on my travels around the state yesterday, most farms had a field or part of a field under water, significant erosion, and large gulleys. Regardless of the cause of the damage, the key to survival and regrowth is the health of the growing point. If recovery from the whorl is not visible within four or five days of improved soil conditions, then counts of healthy plants should be made and replanting decisions considered. The cool temperatures that we saw yesterday and today, after the damage, slowed both the recovery and deterioration of the corn, which may force us to wait a few extra days before making an accurate assessment of the field.
When you evaluate your corn stands, first you need to determine the plant population in the field (count the plants in a row length equal to .001 of an acre to determine population), then you need to evaluate plant health three or four days later, assess the unevenness of stands, compare the yield of a reduced stand to that of a replanted stand, calculate replanting costs, and evaluate the risk factors of replanting. Optimum populations do vary across locations, but these variations are relatively small.
If you are in a situation where corn needs to be replanted because of last weekend's weather, one of the first questions is "How late we can plant full-season corn hybrids in Iowa?" Although delayed planting shortens the growing season, corn hybrids adjust well to this delay. Corn yields do not begin to decline rapidly until planting is delayed beyond mid-May. Based on previous ISU research on corn yield response to planting date, corn yield will be about 70 percent of the relative yield potential compared to corn planted at the optimum window (April 20 to May 5).
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. Generally speaking, if corn planting is delayed until June 10 to 15, very early maturing corn hybrids should be used; after June 10 to 15, corn planting is risky unless the corn can be used for silage. If you decide to switch to another crop, such as soybean, please remember that the corn herbicide program that you used earlier may not allow you to plant soybean.
For more information on corn planting in Iowa, refer to PM 1885: Corn
Planting Guide, available at https://www.extension.iastate.edu/Publications/PM1885.pdf.
Additional resources to help crop producers make decisions on how to handle
hail- and flood-damaged crops can be found on the Web at: https://www.extension.iastate.edu/ag/flooding.html.
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