Assessing Re-Plant and Maturities • 5.13.19

Brandon Nystrom

Assessing Re-Plant and Maturities

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Cold. Wet. Frustrating. I think that pretty well sums up the last couple of weeks for farmers in Missouri, Iowa and the majority of the Midwest. As indicated by the May 5th USDA Crop Report Missouri is an estimated 49% planted. This is well under the 5 year May 5th average of 74%. While there’s a lot to be done and the clock is certainly ticking, hope is not all lost. If the forecast holds true this week should bring a little sunshine and some much needed GDU’s to the area. With that said, not all of the corn in the ground is necessarily in good health.

Does “Rowing corn” mean a good stand?

Often when I ask a grower about their stand they reply “Good, I can row it from the road”. While it is certainly true that seeing those little green rows pop up makes a farmer feel good inside, it doesn’t always mean they have a good stand. It’s hard to find skips, disease and unevenness from a road side. Many times, I’ve witnessed growers perplexed at a fields poor harvest in the fall due to issues that occurred in April/May.  Why is it important to have an even stand? Interplant competition and skips can greatly reduce yield. According to the University of Minnesota (Coulter; 2012), unevenness from delays in corn emergence can decrease yield 5-9%. Both Nafzinger (1996) and a Doerge (2002) found that having 10% skips in a field corresponded to an 8%+ yield decrease. These are big numbers.

Alive or dead? (Struggling corn seedlings)

The first question for anyone considering a re-plant is “Are the plants alive?”. Under saturated conditions, corn is most susceptible to death during the germination and emergence stage.  Prolonged periods of saturated soil (and compaction from heavy rains) can reduce germination and emergence due to lack of oxygen. After 48 hours of soil saturation, soil oxygen is depleted and critical plant functions (photosynthesis, water and nutrient uptake) are impaired. Thus, young corn plants are more susceptible than corn beyond the V6 stage when the plants are taller and the growing point is above the surface.

For corn not yet emerged we have to evaluate the appearance and integrity of the seed and seedling. A seed that is discolored and soft is most likely starting to rot and will have a rotting odor when broke open. For corn that has emerged, new leaf growth is a sign the plant is still functioning.  If new leaf growth is slow to develop, evaluate the health of the growing point located in the crown area of the plant just below the soil surface which should appear white/cream colored.

2019 example: Below are two pictures from a farm I visited last week where the grower was strongly considering a re-plant. This farm had received roughly 230 GDU’s and the corn was just barely poking through. Since we know it takes roughly 110 GDU’s for corn to emerge, why wasn’t it already up? My best answer was a lack of oxygen due to the continual rainfall (3”+) since the planting date. After observing multiple parts of the field, the majority of seedlings were still alive and the seeds were firm. Most appeared to be at the same growth stage. The only concerns I had were the parts of the field at the bottom of slopes. A couple days of sunshine today and tomorrow should reveal a lot. 

Replant Decision Making Guide

The guide below is from the University of Illinois 04-05 Agronomy Handbook. While this isn’t Gospel, it does help us when considering the costs of re-planting. The later we get in May the less time we have to maximize yield potential with a new stand. And while often necessary, there are no guarantees things go better the second time around.

Should we switch maturities?

This is another common question I receive. For me, the answer for most growers in Missouri and southern Iowa (for now) is a hard “NO”. I personally wouldn’t start worrying about maturities until we get closer to June. There is still plenty of time for us to take advantage of the superior germplasm found in the full season maturity hybrids. I would hate for growers to leave potential yield on the table with the market we are in, especially if we have a favorable summer as several forecasts predict. Using A6499 as an example, it takes roughly 2800 GDU’s for this hybrid to safely reach physiological maturity. The WeatherTrends360 forecast model we would reach that on September 1st if planted today (May 13) in Columbia MO.

Below is a great article from Dr. Bob Nielsen at Purdue on hybrid maturity and delayed planting:

Purdue’s research indicates a decreased need in GDU’s in hybrids with delayed planting. Their claim is that hybrids planted after May 1 need roughly 6.8 less GDU’s for each day delayed after May 1 through the middle of June. Example: If you planted A6499 on May 20 it would take (6.8 x 20) 136 LESS GDU’s 2800 – 136 = 2664 total) to reach maturity.

Bottom line: Don’t switch off a high yielding full season hybrid in fear of planting date until late May/early June. If a grower wants to shorten up a little from a very long season (118 day) corn to something a little less full (111-115 day) that’s reasonable. Drying costs/ability obviously play a factor.


Coulter, J. 2012. Planting Date Considerations for Corn. Minnesota Crop News. Univ. Of Minnesota Extension.

Doerge, T.A., Hall, T. and Gardner, D. 2002. New research confirms benefits of improved plant spacing. Crop Insights, Vol. 12, No. 2. Pioneer.

Nafziger, E.D. 1996. Effects of missing and two-plant hills on corn grain yield. J. Prod. Agric., 9:238-240.

Image 1

Pictures from a farm where a grower was strongly considering re-plant

Image 2

Guide to consider replant costs from U of I 04-05 Agronomy Handbook

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