Many fields across the area experienced hail damage from this week’s storms that has led to concerns with corn and soybean stands, survival and their impact on final grain yield.

• What is and will be the final stand of the corn field?
• How healthy is the corn plant?
• Given the current stand and defoliation, how much yield impact will the reduced stand have?
• Should the crop be replanted?
• What are the replant options for corn or soybeans?

The growing point on corn is below ground until V5 (5 leaf collars visible). Prior to this time corn will generally re-grow from hail damage. Data from the National Crop Insurance Service’s "Corn Loss Instructions" indicate that less than 11 percent yield loss will occur with 100 percent defoliation up through the eight leaf stage .

To evaluate the location and health of the growing point, make a horizontal cut through the corn plant and look for the "small triangle" near the base of the plant. The tissue should be white in the center. Sometimes even though the growing point was not cut off, diseases set in after the hail and causes rot to occur. Generally, some re-growth from the growing point can be seen 3-4 days after the hail.

Use the following table to determine the length of row to evaluate corn populations.

Determining Yield Loss Due to Stand Reduction

When a hailstorm occurs early in the growing season, an accurate stand reduction assessment is important if replanting is a management option. Because it is difficult to distinguish living from dead tissue immediately after a storm, the assessment should be delayed for a week to 10 days. By that time, re-growth of living plants will have begun and discolored dead tissue will be apparent. (Another reason for delaying assessment is that some plants initially surviving a storm may soon die because of disease infection entering at the sites of plant damage.) To get an accurate estimate of the extent of damage, observe and sample plants from at least three parts of affected fields, totaling about 1/100 acre

Table 2 is based on research on stands and planting dates by Dr. Dale Farnham (ISU Extension corn specialist). Although results will vary somewhat due to location, season, hybrid, and other factors, Table 2 serves as a good starting point in decision-making.

Once you have evaluated stand level and uniformity, compare that yield percentage with a full stand at the expected replant date. Convert the difference to bushels per acre. If the replant yield is lower, do not replant. If it is greater, consider the cost of replanting (tillage, planting, seed, and other factors) to see if the extra yield is enough to make replanting profitable.

Additional considerations:

• If you tear up a marginal stand, what will be the affect on your rotation? By replanting to soybeans, you’ll have second year soybeans on some fields. Will soybean cyst nematode or soybean diseases become a serious problem? An estimate is that soybean yields are reduced by 10 percent when following a previous crop of soybeans.
• What herbicide has been applied to the field already? Refer to the herbicide label to determine rotations period for soybeans. Or refer to the on-line document Replant options following herbicide applications by Brent Pringnitz, extension program specialist and Bob Hartzler, extension weed scientist, Department of Agronomy. The document can be accessed on-line at http://www.ipm.iastate.edu/ipm/icm/1998/6-8-1998/replant.html

http://www.agcom.purdue.edu/AgCom/Pubs/AY/AY-264.html

1. Length of row equal to 1/1000th acre (from Table 1, based on a row width
   of _____in.): ________ ft.-in.
2. Number of live plants in three 1/1000th-acre lengths Site 1 Site 2 Site 3 Site 4 of
   row: (1st)____ +(2nd) _____ +(3rd)_______ = ______ ______ ______ ______
3. Average plants per 1/1000th acre (#2b / 3 rows): ______ ______ ______ ______
4. Average live plants per acre for site (#2c x 1000): ______ ______ ______ ______
5. After-damage plant population for all sites inspected (sum of #2d at each site / number of sites):
   _______plants/a.

1. If common gap size (#3) is more than 3 feet, enter 5%; if it is less than 3 feet,
   enter 2%: ________% yield loss

1. Planned seeding rate: _____________ seeds/a.
2. Seed germination percentage (from seed tag):________%
3. Expected plant survival rate (use 95% if you're not sure): ________%
4. Replant target population (#14a x #14b x #14c):___________plants/a.

Step 16. Yield gain or loss from replanting 

1. (#15)______% - (#13)________% = ______% of optimum yield
2. If there is a yield loss, replanting is not warranted and should not be done. If there is a
   yield gain, go on to Steps #17 and #18.

by Brent Pringnitz, extension program specialist and Bob Hartzler, extension weed scientist, Department of Agronomy. http://www.ipm.iastate.edu/ipm/icm/1998/6-8-1998/replant.html

¹ Only if safener-treated seed is used.
² Do not rework soil.
³ Liberty-Link only.
⁴ Rework soil, if necessary. Plant below depth of tillage.