Is a Flag Test in Corn of any Value?

Ok…What is a flag test? Simply, it is a way to look at and determine factors that influence corn seed emergence and the affect that it has on yield. This test takes a little time going to the field every day watching for your seed to germinate and emerge.  Once you start you will see a lot of things that you’ve never given much attention. I will write more on the techniques in just a minute but let’s look at why it is called the flag test and the results of your potential findings. Is it worth it?  I give it a resounding yes.

Corn seed emergence studies have been conducted for decades but the “flag test” was popularized back in 2014 and 2015 when Mr. Randy Dowdy broke yield records in Georgia and nationally.  Having been invited to speak on his success around the U.S., he challenged growers around the country to observe and monitor seed emergence in their fields over a span of a few days as one of the first steps to success. 

Armed with previous scientific studies that delayed emergence in corn usually led to yield loss, Randy had observed delays in his field and was curious as to how much that had cost him in yield.  His observations led him to a better understanding of the importance of obtaining an even emerging stand as possible.  Ultimately, he would take a length of row, say 1/1000th of an acre and observe every 12 hours from the first seed in emergence to the last. He did this in several areas.  He would flag each seed that emerged in 12 hour increments with different color flags over several days until all emerged.   He would observe over the growing season how delayed plants developed and, ultimately, how that affected the ear development.  At the end of the season, he then collected by row all the ears that were on plants that emerged first, and repeated that till he completed harvesting those plants that emerged last.  What he found told him a lot about the importance of getting the crop up evenly and how he could influence it and how the weather influenced it.

Since then, university and industry agronomists, extension agents, field consultants, and growers, among others have taken an interest in repeating this in their corn field or studies.  It’s not hard to “google” it and find different responses and results. Overall, (depending on a multiplicity of factors) results show the increase in delayed emergence increased the yield loss per plant.  As I reviewed the information I could find around the country, it was clear that corn plants showed disparity in growth pattern (leaf emergence) and subsequent ear development (rows per ear, number of kernels per row, and kernel weight) with varying results on yield impact.  A common theme is clear as corn plants emerge over a three to four day period, the yield per plant is significantly challenged. In studies across, Georgia, North Carolina, and Virginia, I saw about a 25-28% loss in kernel numbers when plants emerged in excess of 24 hours of each other. In Virginia, a three-year study demonstrated a 72% reduction in ear weight in plants that emerged four days later than the first plants. Another three-year study showed corn yield losses were 8 and 15 bushels per acre and even higher when emergence was delayed 2 and 3 days, respectively.  And to be fair, I’ve reviewed studies that demonstrated less loss particularly with only 1 to 2 days delay. All of these studies demonstrated that many factors were involved in seedling emergence.  The total yield loss is dependent on the percentage of plants that were negatively affected by emerging later than their neighbor.  Needless to say, this makes you want to understand why some seeds are emerging later than others.   A 5-8 bushel per acre loss can cover quite a bit of territory when corn is over $5 per bushel.

Note the differences in emergence of the individual seeds.
Note the differences in emergence in the plants above. Two in the middle are days behind.

Going back to a comment I heard Randy say in one of his presentations, “Don’t be the limiting factor in your yield”, is a philosophy I hope is in every grower’s mind when he begins his next planting season.  Don’t be the limiting factor.  Do everything possible to achieve even emergence whenever possible. Dr. Mark Westgate, retired Corn and Soybean Physiologist, Iowa State, told me once, corn makes bad neighbors.  He is right.  A plant that is delayed in emerging may end up being a weed.  In other words, never producing an ear to contribute to yield.  That plant took up space that the neighboring plants could have used to compensate for the open space.  It competed for light, nutrients, water and just existed. 

Is the flag test of value?  Absolutely! In fact, the more time you take to explore the more you learn about potential sins you may commit during planting season.  Planting sins such as poor soil preparation, poorly adjusted equipment (lack of depth control and placement, downforce, spacing, vacuum setting, etc.) and planting speed will affect the placement of seed in furrow and influence how they emerge.  Soil compaction, low soil oxygen conditions, weed competition, root and foliar diseases, insects, nematodes, nutrient deficiencies and low soil pH all partner in reducing the yield potential in corn.    

If you conduct a flag test, go back to the field frequently during the season.  Make sure you record the GDU’s to emergence and as the plant grows and take copious notes over time. A week to ten days after the last plants emerge, dig a few plants outside your test area where seeds have emerged at different times.  Check to see if they were planted at the same depth. If not, there could be an equipment problem, a speed problem, a downforce problem, dry dirt falling back on the seed prior to furrow closing, or maybe it was trash pinnng.  You may notice that it’s worse in one row vs another.  Was it a planter unit not being adjusted right?  Or fertilizer too close the row? Was the seed placed over the subsoiler foot? The furrow not sealing right?  Herbicide injury? Nematode problem?  Insect injury?  As the plants mature, note the differences in number of leaves and the size of the plant.  Pay attention to the ear placement at silking.  Are they at different heights? Make sure to harvest each individual plant within the correct window of emergence and note number of rows, number of kernels per row, measure kernel number and total weight and then determine the differences in weight and yield.  Look back at your notes and think about each factor you noted and look for those things that you can possibly improve the outcome the next season.  The more time you take, the better you are able to understand the factors that will affect emergence.

Yes, knowledge is valuable to success.  Take the time to study your crop whether it is corn, cotton, peanuts or whatever.  The more you look and see, the better you will be in knowing if you did it right.  Build on that success.  Don’t be the limiting factor.

Conducting your own flag test:

1). First, make sure you have four to five different color flags.  You may only need three but more have more colors ready.

2). Pick an area to record plant emergence.  Some growers choose to count 1/1000 of an acre or smaller in several areas. In a 36 inch row, 1/1000 of acre is 14 feet, 6 inches.  In a 30 inch row, 1/1000 of an acre equals 17 feet and 5 inches.  Choose an area that you can return to repeatedly over the season.  Mark it well so as not lose it because the plants are tall and will obscure the flags when the crop is silking.

3). A few days after planting, begin looking for the first seedlings to emerge about 1/8 inch above the soil. (Remember: Corn seedlings take between 70 & 120 GDU’s to germinate and emerge depending on many factors.  Planting when the soil temperatures are ~55 degrees, typically lengthens the time frame to 7 to 12 days.)  Once this happens, then count the total corn plants that have emerged in a specified row or area that you have chosen to mark and record.  Place a flag (all one color) by every plant and return every 12 hours and continue with different colored flags each time until the last plant emerges. Most of the time, it will take only 4 to 5 days before all the seedlings emerge once it begins. Record all you findings.

NOTE: Some growers conduct flag tests over each 12-hour segments, others every 24 hours.  In southGeorgia, during early March, sunrise is about 7:00 am and sunset about 6:40 pm so 12 hour segments are realistic. 

4). Observe the area frequently recording what you see.  Count the number of collared leaves around V6-V7, note any differences between flag colors.

5).  At silking, compare the differences in ear height, noting differences.

6).  Prior to general field harvest, take several buckets and harvest all the ears of each color separately. Count and weight the ears to get an accurate yield of each time difference.  If you are interested, have someone count the number of rows per ear and take a sample to count kernel numbers per row.

7).  Note the differences in the number of plants and the number of ears of each color. Some plants may have two ears.  In late emerging plants, some plants may not have an ear.

8). Use the data to consider all the factors that may have affected your results. 

Final note: Over the last two weeks, I’ve noted some great information out of Tifton UGA campus scientist. Check out Dr. Simer Virt’s blog on precision ag, regarding spinner disk spreaders, https://site.extension.uga.edu/precisionag/ and also Dr. Eric Prostko’s blog piece on reminders before planting field corn, https://ugaweedscience.blogspot.com/

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