Growing Degree Days vs. Calendar Days – How Long Will Emergence Take?

Source: Alexander Lindsey, Greg LaBarge, OSU Extension

When we examine crop emergence post-planting, two factors can impact speed of emergence – soil moisture content and soil temperatures. If soil temperatures are lower, it can take more calendar days for emergence to occur meaning rowing corn may take a little more time. In the Ohio Agronomy Guide, emergence should begin to occur after approximately 100 air GDDs.

A difference in 10 degrees in temperature can dramatically affect how quickly crops will emerge. For example, at a temperature of 60 degrees F heat unit accumulation per day would be 60 F – 50 (base temperature for growth) = 10 GDDs. If it takes 100 GDDs to start to see emergence, at this rate it would take 10 calendar days to see the crop start to emerge. If temperatures are 70 degrees F, heat unit accumulation per day would be 70 F – 50 = 20 GDDs. This would shorten the emergence window to 5 calendar days instead, resulting in more rapid emergence from planting.

Figure 1. Emerged corn on May 6, 2021 planted April 19 near London, OH.

In recent work from Nemergut et al. (2021), researchers from OSU observed emergence starting at 110 to 120 soil accumulated GDDs (base of 50 degrees F) for corn, which equated to first emergence observed in 4 or 5 days after planting. Some of the difference in calendar date for emergence (though GDD accumulation was similar) was because planting depth was changed, and the 1” planting accumulated GDDs faster than the 2” and 3” planting depths. These studies though were planted in May or early June (2019 wet spring delayed planting), and daily accumulated GDDs was higher than we might expect if planted in late April. Soil accumulated GDDs have been discussed above, and these could vary slightly compared to air accumulated GDDs (calculated using air temperatures). In the work referenced above, accumulated air GDDs in the first four days post-planting were 106-118 GDDs, slightly less than the soil accumulated GDDs.

If you want to predicate emergence on your farm, the GDD calculator found at is a useful tool. It is a two-step process, first find your location on the map, then enter your planting date. The graph will display accumulated GDD’s for your location. Example output in Figure 2 shows GDD accumulation from an April 19, 2021 planting date near London, OH in Madison County. By May 6 the accumulated GDD was 138 and the emerging corn is shown in Figure 1. The GDD calculator can be used to predict growth stage throughout the growing season. This is a handy to time when scouting and management decisions should be made.

Figure 2. GDD accumulation from April 19 to May 6, 2021 near London, OH.

As the days turn cooler, don’t be surprised if the crops don’t pop out of the ground quickly due to lower soil temperatures. If emergence is still not observed after two weeks, it may be worth checking the field to see if other issues may be affecting emergence.

Challenges Ahead

Source: Jim Noel, NOAA

There are challenges ahead so we will break them into short-term and long-term.


The recent snow was a rare event for the amount that fell across Ohio. However, the minimum temperatures in the 20s and 30s was not that far off of normal for last freeze conditions for Ohio.

The strongest typhoon ever in the northern hemisphere occurred east of the Philippines last week and this energy will come across parts of North America over the next week. When that happens weather model performance often drops. Hence, if you see more bouncing around of forecasts the next 10-15 days that may be one reason why.

We have a big warm-up the first half of this week ahead of a strong storm that will move through Ohio the second half of the week with wind and rain. We could see anywhere from 0.50 inches to over 2 inches across Ohio later this week but placement is not certain and seems to favor central and southern Ohio with the highest amounts. Expect most places to see an inch or less given recent track record of events coming in lighter.  Once the storm passes colder air will push in and some frost will be possible this weekend with lows in the 30s.

The rainfall the next 30-days is critical for the growing season as moderate drought over northern Ohio already has soil conditions in a shortage.

The latest drought monitor can be found here:

Also, some of the greatest evaporative demand in the country has been in parts of northern Ohio the last 30+ days and can be monitored as a leading indicator for drought development at this webpage via NOAA:

You can keep up on the Ohio River Forecast Center’s Water Resources Outlooks at:


May appears will see periods of well above and below normal temperatures but will average out close to normal or just slightly above normal. Precipitation continues to trend at or below normal but models suggest a normal May for precipitation. If we get timely rains that will help soil conditions for summer. If we miss critical rains in May, this could lead to summer issues.

The latest rainfall outlook for the next 16-days is viewable in the attached image. Normal rainfall is nearing 2 inches for the next 16-days. We expect 1-3 inches for most areas.

For summer, most climate models indicate above normal temperatures and medium to high confidence of above normal temperatures during typical peak temperatures from mid-June to mid-August. We will need to monitor this. Confidence in summer rainfall is low. Most outlooks and models suggest not too far from normal rainfall but the reality is since 30-50% of summer rainfall comes from local soils, the next 30-days will be a big player in our summer rainfall outcome.

Soil Moisture & Corn Seed Depth

Source: Dr. Bob Nielsen, Purdue Univ.

Bottom Line: Uniformly adequate soil moisture at seeding depth is important for assuring rapid and uniform germination of a newly planted corn crop. Take time to assess soil moisture at your selected seed depth on the day of planting. If soil moisture is not available or unevenly available at your normal seeding depth, then consider planting deeper than normal if soil moisture is available at those deeper settings.

Uniformly adequate soil moisture at seeding depth is important for assuring rapid and uniform germination of a newly planted corn crop. Take time to assess soil moisture at your selected seed depth on the day of planting. If soil moisture is not available or unevenly available at your normal seeding depth, then consider planting deeper than normal if soil moisture is available at those deeper settings.

Choice of seeding depth for corn is often paid scant attention by growers during the rush of planting their crop. Human nature being what it is, we tend to simply leave the planter’s depth control setting at the same position as it was in previous years. While it is true that a seeding depth of 1.5 to 2 inches is a fairly all-purpose range that works well in most situations, certain conditions merit more attention to seeding depth, the most common factor being soil moisture.

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Should you expect any freeze damage to winter wheat? Most likely, no.

Source: Laura Lindsey, Alexander Lindsey, OSU Extension

The incoming cold temperatures are not likely to impact winter wheat. The magnitude of freeze damage depends on: 1) temperature, 2) duration of temperature, and 3) wheat growth stage.


Prior to the Feekes 6 growth stage, the growing point of wheat is below the soil surface, protected from freezing temperatures. Most of the wheat in Ohio is at the Feekes 4 (beginning of erect growth) or Feekes 5 (leaf sheaths strongly erect) growth stage and should be unaffected by the incoming cold temperatures, predicted to be mid- to low 20s on Wednesday and Thursday.

At Feekes 6 growth stage, our research has shown only a 5% reduction in wheat yield at a temperature of 20°F for 15-minute duration and 50% reduction in wheat yield at a temperature of 12°F for 15-minute duration. (Although, it should be noted, there is a great deal of variability in response due to environmental conditions for the remainder of the growing season. Additionally, greater soil moisture levels can help buffer against short-term temperature fluctuations.)

For more information on Freeze Symptoms and Associated Yield Loss in Soft Red Winter Wheat, please see our new FactSheet:

Wheat Growth Stages and Associated Management- Feekes 6.0 through 9.0

Source: Laura Lindsey, Pierce Paul, Ed Lentz, OSU Extension

It is important to correctly identify winter wheat growth stages to enhance management decisions, avoiding damage to the crop and unwarranted or ineffective applications. Remember, exact growth stage cannot be determined by just looking at the height of the crop or based on calendar dates. Remember to stage several plants from several areas within your field.

Here, we will focus on staging wheat Feekes 6.0 through 9.0.

Feekes 6.0: At Feekes 6.0 growth stage, nodes are all formed, but sandwiched together so that they are not readily distinguishable. The first node is swollen and appears above the soil surface. This stage is commonly referred to as “jointing”. Above the node is the head or spike, which is being pushed upwards eventually from the boot. The spike at this stage is fully differentiated, containing future spikelets and florets.

Growers should remove and carefully examine plants for the first node. It can usually be seen and felt by removing the lower leaves and leaf sheaths from the large wheat stems. A sharp knife or razor blade is useful to split stems to determine the location of the developing head. A video showing how to identify the Feekes 6.0 growth stage can be found in the video below.

Feekes 7.0: At Feekes 7.0 growth stage, the second node becomes visible. This stage is characterized by the rapid expansion of the head and a second detectable node. Look for the presence of two nodes- one should be between 1.5 and 3 inches from the base of them stem and the other should be about 4 to 6 inches above the base of the stem. These nodes are usually seen as clearly swollen areas of a distinctively different (darker) shade of green than the rest of the stem. The upper node may be hidden by the leaf sheath; you may have to run your fingers up the stem to feel for it. If only one node is present, the wheat is still at Feekes 6.0 growth stage. Wheat will still respond to nitrogen applied at Feekes 7.0 if weather prevented an earlier application; however, mechanical damage may occur from applicator equipment. A video showing how to identify the Feekes 7.0 and 8.0 growth stages can be found here:

Feekes 8.0: At Feekes 8.0 growth stage, the flag leaf is visible, but still rolled up. This growth stage begins when the last leaf (flag leaf) begins to emerge from the whorl. This stage is particularly significant because the flag leaf makes up approximately 75% of the effective leaf area that contributes to grain fill. It is therefore important to protect and maintain the health of this leaf (free of disease and insect damage) before and during grain development. When the flag leaf emerges, three nodes are visible above the soil surface. To confirm that the leaf emerging is the flag leaf, split the leaf sheath above the highest node. If the head and no additional leaves are found inside, Feekes 8.0 is confirmed and the grower should decide whether or not to use foliar fungicides to manage early-season and overwintering fungal diseases. Nitrogen fertilizer applications at or after Feekes 8.0 growth stage may enhance grain protein levels, but are questionable with respect to added yield. Moreover, additional N may increase the severity of some foliar diseases, particularly the rusts.

Feekes 9.0: Feekes 9.0 growth stage begins when the flag leaf is fully emerged from the whorl with the ligule and collar visible. From this point on, leaves are referred to in relation to the flag leaf (e.g., the first leaf below the flag leaf is the F-1, the second leaf below is F-2, and so forth). A video showing how to identify Feekes 9.0 and 10.0 growth stages can be found here:

Corn College and Soybean School

The Agronomic Crops Team will host a virtual Corn College and Soybean School on February 11, 2021. Corn College is in the morning, from 9:00 – 12:00pm, with Soybean School in the afternoon from 1:00-4:00pm. Each program will feature updates from OSU Specialists. CCA CEUs are available. The schedule for the day is as follows:


Corn College, 9:00am-12:00pm

  • Corn Management for 2021, Peter Thomison, 1.0 CM CCA CEUs
  • Meeting Nutrient Needs in Corn, Steve Culman, 1.0 NM CCA CEUs
  • Disease Management, Pierce Paul, 1.0 PM CCA CEUs
  • Insect Management, Andy Michel, 1.0 PM CCA CEUs

Soybean School, 1:00-4:00pm

  • Soybean Management for 2021, Laura Lindsey, 1.0 CM CCA CEUs
  • Weed Management, Mark Loux, 1.0 PM CCA CEUs
  • Disease Management, Anne Dorrance, 1.0 PM CCA CEUs
  • Insect Management, Kelley Tilmon, 1.0 PM CCA CEUs

This program is free to attend. Register at

Estimating Corn Yield

According to the latest Ohio Crop Weather Report 94% of the Ohio corn crop is silking, 6 percentage points ahead of the 5-year average.  39% of the crop is in the dough stage and 1 percent of the Ohio corn crop is dented.

This time of year many of us begin to think about our potential corn yield.  The most popular yield estimator is the  THE YIELD COMPONENT METHOD.  This procedure was developed by the Agricultural Engineering Department at the University of Illinois. The principle advantage to this method is that it can be used as early as the milk stage of kernel development, a stage many Ohio corn fields have probably achieved. The yield component method involves use of a numerical constant for kernel weight which is figured into an equation in order to calculate grain yield. This numerical constant is sometimes referred to as a “fudge‑factor” since it is based on a predetermined average kernel weight. Since weight per kernel will vary depending on hybrid and environment, the yield component method should be used only to estimate relative grain yields, i.e. “ballpark” grain yields. When below normal rainfall occurs during grain fill (resulting in low kernel weights), the yield component method will OVERESTIMATE yields. In a year with good grain fill conditions (resulting in high kernel weights) the method will underestimate grain yields.

In the past, the YIELD COMPONENT METHOD equation used a “fudge factor” of 90 (as the average value for kernel weight, expressed as 90,000 kernels per 56 lb bushel), but kernel size has increased as hybrids have improved over the years. Dr. Bob Nielsen at Purdue University suggests that a “fudge factor” of 80 to 85 (85,000 kernels per 56 lb bushel) is a more realistic value to use in the yield estimation equation today. For more on this check

Step 1. Count the number of harvestable ears in a length of row equivalent to 1/1000th acre. For 30‑inch rows, this would be 17 ft. 5 in.

Step 2. On every fifth ear, count the number of kernel rows per ear and determine the average.

Step 3. On each of these ears count the number of kernels per row and determine the average. (Do not count kernels on either the butt or tip of the ear that are less than half the size of normal size kernels.)

Step 4. Yield (bushels per acre) equals (ear #) x (avg. row #) x (avg. kernel #) divided by 85.

Step 5. Repeat the procedure for at least four additional sites across the field. Keep in mind that uniformity of plant development affects the accuracy of  the estimation technique.

The more variable crop development is across a field, the greater the number of samples that should be taken to estimate yield for the field.

Example: You are evaluating a field with 30‑inch rows. You counted 29 ears (per 17′ 5″ = row section). Sampling every fifth ear resulted in an average row number of 16 and an average number of kernels per row of 33. The estimated yield for that site in the field would be (29 x 16 x 33) divided by 85, which equals 180 bu/acre.

Corn Growth & Development – R3 Milk

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.

R3 – Milk

The R3 (Milk) stage occurs about 18 – 22 days after silking.  At this stage the outside of the kernel is colored yellow while the inside is white.  The kernel contains a “milky” white fluid that will explode when pressure is applied.  Kernel moisture content is approximately 80% and starch is beginning to accumulate in the kernel.

Management/Scouting: Scout for drought symptoms.  Stress can still cause kernel abortions from the ear tip downward.  Insects: Corn Earworm, Corn Rootworm adults and Japanese Beetles Diseases: Eyespot, Gray Leaf Spot, Norther Leaf Blight, Southern Leaf Blight and Tar Spot

Photo Source: Corn Growth & Development, Iowa State University

Corn Growth & Development – R2 Blister

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.

R2 – Blister

The R2 (blister) stage occurs about 10 – 12 days after silking.  At this stage the kernel is visible and resembles a blister.  The kernel is filled with clear fluid, the embryo is barely visible and it is at about 85% moisture.

Kernels are in a rapid period of grain-fill.  Rapid and steady grain-fill will continue through R6.  If severe stress occurs now or during R3, kernel abortion will occur from the tip of the ear downward.  Kernel abortion will continue until the plant has has enough carbohydrates for the remaining kernels.

Silks outside the husk leaves are drying and changing in color from tan to light brown.  The silks will naturally detach from their kernels following fertilization.