How Did Cold Weekend Affect Iowa's Emerging 2010 Corn Crop?

Frost nipped areas of northern Iowa and even dropped down into spots in central Iowa on Mother's Day weekend.

Published on: May 10, 2010

What are the concerns with young corn seedlings or corn that hasn't yet emerged from the ground where frost hit this past weekend? Brian Lang, an Iowa State University Extension field agronomist at Decorah in northeast Iowa offers the following answer and scouting guidelines.

1)  The already germinated corn is fine.  Growing points are below ground.  The most frost injury on emerged leaves will be mostly on no-till (heavy amount of crop residue covering the ground) and sandy soils (light soils retain less heat to insulate from temperature changes).

2)  The only potential concern with the corn is with the recently planted corn.  There is a chance that some of the recently planted corn may imbibe colder water in the germination process causing a chilling effect of the seeds.  This is explained in the May 5 ICM News article at:

Tips for scouting corn and soybeans at emergence

With crop emergence comes time for the first scouting pass, says Lang.  Check to see that planting operations were accomplished as planned, or is there need to make adjustments for next season?  You need to measure plant population, uniformity of planting depth and plant spacing.  Also, if you did not use a pre-emerge herbicide, start identifying weeds to target with the early-postemergence herbicide program. Also, the earliest emerged soybeans should be scouted for Bean Leaf Beetle as discussed at this time.

Plant Population:  You have seen these tables before to estimate plant populations.  For corn use Table 4 on page 4 in the publication at:

For soybeans, use Table 2 in the article at:

Planting Depth:  For corn, check for uniformity of depth. The recommended seeding depth is about 1.75 inches. Planting depth should never be shallower than 1.5 inches. When the surface soil is dry, especially when planting has been delayed until mid- or late May, planting depth may need to be increased to 2 inches or more.

For soybeans, planting depth should be 1 to 1.5 inches and not deeper than 2 inches.  Palle Pedersen discusses this in the following publication:

Plant Spacing:  Look for lack of uniformity in the stand. Too many deviations from normal may results in lower yields. The following article from the University of Wisconsin does a nice job of explaining what a standard deviation is (page 2), and also summarizes their research on factors influencing uniformity of corn stands

If you want to calculate the standard deviation of part of your corn stand, enter into the following web page the inch-spacings of 20 or so corn plants in a row and click "calculate". Do the same for as many corn rows and areas of the field that you care to.

Seedling Health:  While you check seeding depth, you can also evaluate seedling health. The May 4, 2010 ICM News article by Alison Robertson, ISU Extension Plant Pathologist, discusses this topic. Go to: