How to Flag Corn Emergence

Corn Emergence Checkup Provides Yield Clues

Pamela Smith
By  Pamela Smith , Crops Technology Editor
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A simple exercise of flagging as corn emerges can be a diagnostic tool to help tweak planting practices next year. (DTN photo by Pamela Smith)

DECATUR, Ill. (DTN) -- It's the time of year to keep your eye on corn emergence. A simple test of flagging corn as it comes up can provide clues to yield performance and help evaluate whether planting tweaks are needed next year.

The test is done by marking off a section of the field and watching for the first corn spikes to appear after planting. The process requires returning to the field at the same time for several days to mark the new arrivals. Follow the marked section of the field through the season and hand harvest the results.

How much yield loss is associated with inconsistent plant emergence surprises many growers, according to Precision Planting agronomist Jason Webster.

"To maximize the yield of each seed planted, we like to see everything emerge within 12 hours of each other. We've learned through these flagging tests that plants that come up after the first plants emerge never catch up, and it doesn't take long for that yield discrepancy to be significant," he told DTN.

"Think of it like a big family sitting down to the dinner table. If you are the last to get your hand on the food, there's not much left," Webster said.

Precision Planting sends out free emergence flagging kits upon request. Any kind of marking system will do though. Colored flags are often available at local farm or construction stores.

Webster has tested the practice for the past three years (2020 to 2022) at the Precision Technology Institute (PTI) test farm near Pontiac, Illinois. What he's found is a 24-hour delay in emergence in those rows results in a 9% loss of yield, compared to the first emergers. After 36 hours, the yield loss is around 38%. A delay of 48 hours knocked 83% off final yield, and emergence beyond 48 hours from the first spike resulted in a 90% yield loss.

"Those bigger corn siblings just get established and have the opportunity to get more water and nutrients," Webster noted. "There's not as many resources left for the 'runts' in the row."

The PTI farm has averaged near 70% emergence in that first 12-hour window over the past three seasons.

Walk down the row you've marked in season and some visual differences of the delays might be evident, as well. Ear set and overall plant height may vary as a result. Those plants last to emerge are often taller as they try to fix their diminished situation. Those plants that emerge after 48 hours may only produce a nubbin or be barren, Webster said.

A bigger question is what causes the latecomers, and can they be prevented? "We've tried every fertilizer we can think of and all sorts of things to give that seed the best opportunity to get out of the ground as fast as possible," Webster said. "I would say 50% of the time, the delay is the result of the closing system (on the planter)."

Seed orientation is another culprit, he said. While very few things in life happen 100% of the time, the way a corn plant germinates and emerges is always the same. The radicle root emerges near the tip of the kernel. The coleoptile emerges from the embryo (germ) side of the kernel and elongates in the opposite direction toward the dent end of the kernel.

When a corn kernel is planted with the tip pointed downward in the furrow, the emerging root (radicle) and shoot (coleoptile) are already positioned in the direction they need to grow.

"If we get plenty of growing degree units (GDU) and warm weather, it may not make that much difference," Webster observed. "But when conditions are cold and wet, the additional energy required to make a U-turn to orient growth exacts a penalty. Dig up a late-emerging plant and chances are it often started life as an upside-down seed."

In a 2022 field demonstration conducted by Pioneer agronomists, seeds planted with the kernel tip down emerged about 20 GDUs earlier than those planted with the tip up. Read more here:….

Currently, there's no sure way to guarantee that a kernel gets planted tip down. Webster stressed the importance of fine-tuning planters and getting seed-to-soil contact. Seed firmers that tuck the seed into the furrow while eliminating air pockets are thought to help. Electronic furrow sensors are generating more information on what's happening in the row that may help refine operations, he said.

"I'd say we're still in the investigative mode on a lot of this and what we can do about it," Webster said. "Flagging gives you information, especially if you've recently changed something in your planting system.

Planters rolled early this year in some areas, but there's still time to try flagging a few fields. "Most farmers make the mistake of trying it in only one field and only in one spot in a field, but almost everything influences emergence. So, I recommend multiple flagging sites within a field," he said.

Webster prefers to mark plant emergence every 12 hours. "As soon as we near 100 GDU's post planting, we're out looking for those spikes. As far as the flagging goes, be consistent and conduct the flagging at the same time each day," he said.

Here's how to do the corn flag test.

-- Measure off 1/1,000th of an acre that is representative of the field (17 ft. 5 inches in 30-inch rows; 26 ft. 2 inches in 20-inch rows; 34 ft. 10 inches in 15-inch rows).

-- Place a colored flag beside the first set of corn seedlings as they spike.

-- Return to the field 12 hours later and mark the next group of emerged plants with a different colored flag.

-- Return every 12 hours to mark the subsequent waves of emerged corn plants until the test row is fully emerged.

-- Harvest the plants according to the day of emergence and record the weight and yield differences to verify if emergence mattered.

Find other DTN articles on the importance of flagging the crop here:… and here:….

Videos from Precision Planting on how to track emergence can be found here:….

Order a Precision Planting emergence flagging kit here:….

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Pamela Smith

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