Common Causes of Low Grain Test Weight

Source:  Allen Geyer, Rich Minyo, Peter Thomison, OSU

Early morning frost on corn Source: Purdue Univ.

Ohio saw record late corn planting in 2019.  According to the Agricultural Statistics Service, only 33% of Ohio’s corn was planted by June 2.  The question being asked now is will the June planted corn reach physiological maturity (black layer) before a killing frost?  Corn is killed when temperatures are near 32°F for a few hours and when temperatures are near 28°F for a few minutes.

A useful tool is available from the Midwestern Regional Climate Center (the U2U tool, available at:  https://mrcc.illinois.edu/U2U/gdd/) that uses current and historical weather data to predict when corn will reach black layer.  The user selects the geographic location that they are interested in, actual planting date and the adjusted relative maturity of the planted hybrid.

Previous studies have indicated that the GDD requirement of late planted corn to reach black layer from planting is less than the requirement of corn planted on a “normal” date.  Keeping this in mind, Dr. Bob Nielsen from Purdue University has developed an adjustment to the GDD requirements for late planted corn.  This calculator can be found at:  https://www.agry.purdue.edu/ext/corn/news/timeless/hybridmaturitydelayedplant.html  Using this calculator, enter the adjusted GDD value in the U2U tool in the “Black Layer GDDs” line.

We have used the U2U tool to predict whether our corn research will accumulate enough GDDs before a killing frost.  Table 1 shows the results of using these tools for the 2019 Ohio Corn Performance Test sites (OCPT) as well as a late planted demo plot that was planted at Hoytville.  These results are based on a 109-day (2618 GDD) hybrid.  The table indicates the planting date, adjusted GDD requirement for the 109 day hybrid, whether physiological maturity (black layer) will be achieved before frost, the predicted black layer date and the average 32° and 28° frost dates.  Because of the adjusted GDD requirements with later planting dates, the predicted GDD accumulations will exceed or just meet the required GDDs before the average frost date for all 10 OCPT sites, including the 5 sites that were planted in June.  We hope that these predictions come true!  Note that the demo plots at Hoytville that were planted on June 27 will not reach black layer before a killing frost based on the U2U tool.

Table 1.  Planting date, Adjusted Hybrid GDD Requirement, Reach BL Before Frost, Predicted Black Layer (BL) Date, and Average Frost Dates for 2019 Ohio Corn Performance Test sites.

Source: Dr. Peter Thomison, OSU

Many corn growers may encounter slower than normal drydown this fall due to late crop development associated with June planting dates. Much of Ohio’s late-planted corn may not achieve black layer until mid-October or later when drying conditions are less favorable for drydown.  Once corn achieves physiological maturity (when kernels have obtained maximum dry weight and black layer has formed), it will normally dry approximately 3/4 to 1% per day during favorable drying weather (sunny and breezy) during the early warmer part of the harvest season from mid‑September through late September. By early to mid‑October, dry-down rates will usually drop to ½ to 3/4% per day. By late October to early November, field dry‑down rates will usually drop to 1/4 to 1/2% per day and by mid-November, probably zero to 1/4% per day. By late November, drying rates will be negligible.

Estimating dry‑down rates can also be considered in terms of Growing Degree Days (GDDs). Generally, it takes about 30 GDDs to lower grain moisture each point from 30% down to 25%. Drying from 25 to 20 percent requires about 45 GDDs per point of moisture. In October, we typically accumulate about 5 to 10 GDDs per day. However, note that the above estimates are based on generalizations, and it is likely that some hybrids may vary from this pattern of drydown. Some seed companies indicate considerably lower GDDs for grain moisture loss, i.e. 15 to 20 GDDs to lower grain moisture each point from 30% down to 25% and 20 to 30 GDDs per point from 25% to 20%.

Past Ohio research evaluating corn drydown provides insight on effects of weather conditions on grain drying. During a warm, dry fall, grain moisture loss per day ranged from 0.76 to 0.92%. During a cool, wet fall, grain moisture loss per day ranged from 0.32 to 0.35%. Grain moisture losses based on GDDs ranged from 24 to 29 GDDs per percentage point of moisture (i.e., a loss of one percentage point of grain moisture per 24 to 29 GDDs) under warm dry fall conditions, whereas under cool wet fall conditions, moisture loss ranged from 20 to 22 GDDs. The number of GDDs associated with grain moisture loss was lower under cool, wet conditions than under warm, dry conditions.

Weather related crop stress may affect drydown this year. Dr. Bob Nielsen at Purdue University notes, “When areas of fields die prematurely due to stresses like drought, spatial variability for grain moisture at harvest can be dramatic and often creates challenges with the management of the grain dryer operation. This is especially true early in the harvest season when grain moistures of healthier areas of the field are in the low 20’s. The spatial variability for grain moisture decreases later in the harvest season as grain moistures throughout the field settle to an equilibrium level (15% or less).”

Agronomists generally recommend that harvesting corn for dry grain storage should begin at about 24 to 25% grain moisture. Allowing corn to field dry below 20% risks yield losses from stalk lodging, ear drop, ear rots, insect feeding damage and wildlife damage.

For more on grain drydown, check out the following article by Dr. Nielsen.

Nielsen, R.L. 2018. Field Drydown of Mature Corn Grain. Corny News Network, Purdue Univ.
URL: http://www.kingcorn.org/news/timeless/GrainDrying.html [URL accessed Sept. 23, 2019].

Source:  Peter Thomison, OSU

Lately I have received questions as to whether corn at various stages of development, especially the blister (R2) and dough (R4) stages, will mature before the 50% average frost date. According to the National Agricultural Statistics Service, as of August 18, 37 percent of Ohio’s corn acreage was in the dough stage (R4) compared to 70 percent for the five year average, and three percent of the corn acreage was in the dent stage (R5) compared to 21 percent for the five-year average. Many areas of the state corn are considerably behind the five-year average because of late planting. Late maturation of the corn crop had led to questions about the likelihood for frost damage and whether more fuel will be needed to dry corn.

Physiological maturity (R6), when kernels have obtained maximum dry weight and black layer has formed, typically occurs about 65 days after silking. At physiological maturity (kernel moisture approximately 30-35%), frosts have little or no effect on the yield potential of the corn crop.

Dr. Bob Nielsen has summarized research findings from Purdue University and Ohio State University that provide insight into both the calendar days and thermal time (growing degree days, GDDs)  typically required for grain at various stages of development to achieve physiological maturity (kernel black layer, R6). This research was conducted at two locations in Indiana (west central and southeast) and two locations in Ohio (northwest and southwest) with three hybrids representing 97, 105, and 111-day relative maturities planted in early May, late May, and mid-June. The calendar days and thermal time from silking to black layer for the 111-day hybrid maturity are shown in Table 1 from http://www.agry.purdue.edu/ext/corn/news/timeless/RStagePrediction.html. The calendar days and thermal time from silking to black layer for the 97-day hybrid and 105 maturity are also available from this Purdue webpage.

The study indicated that corn planted in mid-June compared to early May requires 200 to 300 fewer GDDs to achieve physiological maturity.  According to Dr. Nielsen, while slightly different responses among the four locations of the trial existed, there did not seem to be a consistent north/south relationship. Therefore, growers can use the results summarized in the following table to “guesstimate” the number of calendar days or heat units necessary for a late-planted field at a given grain fill stage to mature safely prior to that killing fall freeze.

How many GDDs can be expected from now until an average date of a killing

frost for a 111-day hybrid planted in mid-June?  To answer this question, estimate the expected GDD accumulation from Aug. 19 until the average frost date (50% probability) for different regions of the state (Table 2).  These GDD expectations are based on 30-year historical normals reported by the Ohio Agricultural Statistics Service. The GDD accumulation was calculated using the 86/50 cutoff, base 50 method.

If you want to determine the “youngest stage of corn development” that can safely reach black layer before the average frost date at a given weather station, use the information in Table 2 on remaining GDDs in conjunction with Table 1 which indicates GDDs needed to reach black layer at various stages of grain fill. Compare “GDDs remaining” for the site with the GDDs required to achieve black layer depending on the corn’s developmental stage.

Table 2. Estimated GDDs remaining from Aug. 9 to the first fall frost for Ohio.

If your corn is in the milk stage (R3) as of Aug. 19, will it be safe from frost? Table 1 indicates that corn planted in mid – June required about 681 GDDs to reach black layer from R3 and Table 2 indicates that all regions of the state can accumulate that number of GDDs before the 50% frost date.

However, if your corn is in the blister stage (R2) as of Aug. 19, it might be a different story. The kernel development – GDD accumulation relationships in Table 1 indicate that corn planted in mid-June that is at R2 needs about 781 GDDs to reach black layer. Table 2 indicates that three regions of the state, South Central, Central, and Southwest, accumulate that number of GDDs before the 50% frost date. Several other regions, West Central, and Southeast, come close to accumulating this number whereas, the Northeast, Northwest, and North Central regions are least likely to accumulate the GDDs required to achieve physiological maturity.

The research results in Table 1 demonstrate that late-planted corn has the ability to adjust its maturity requirements, and most of this adjustment occurs during the late kernel development stages. In previous growing seasons when GDD accumulation was markedly less than normal, corn planted by mid-June has usually achieved physiological maturity before the first frost occurred.

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.  Throughout the growing season I will discuss the various corn growth stages and management issue at each stage. 

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

Source: Peter Thomison, Alexander Lindsey, OSU

Night time temperatures can affect corn yield potential. High night temperatures (in the 70s or 80s degrees F) can result in wasteful respiration and a lower net amount of dry matter accumulation in plants. Past studies reveal that above-average night temperatures during grainfill can reduce corn yield by reducing kernel number and kernel weight. The rate of respiration of plants increases rapidly as the temperature increases, approximately doubling for each 13 degree F increase. With high night temperatures more of the sugars produced by photosynthesis during the day are lost; less is available to fill developing kernels, thereby lowering potential grain yield. High night time temperatures result in faster heat unit or growing degree day (GDD) accumulation that can lead to earlier corn maturation, whereas cool night temperatures result in slower GDD accumulation that can lengthen grain filling and promote greater dry matter accumulation and grain yields.

The Pioneer Insight article referenced below concludes….

“Although higher night temperatures undoubtedly increase the rate of respiration in corn, research generally suggests that accelerated phenological development is likely the primary mechanism affecting corn yield.”

Research at the University of Illinois conducted back in the 1960’s indicated that corn grown at night temperatures in the mid-60s (degrees F) out yielded corn grown at temperatures in the mid-80s (degrees F). Average corn yields are generally much higher with irrigation in western states, which have low humidity and limited rainfall. While these areas are characterized by hot sunny days, night temperatures are often cooler than in the Eastern Corn Belt.  Low night temperatures during grain fill (which typically occurs in July and August) have been associated with some of our highest corn yields in Ohio. The cool night temperatures may have reduced respiration losses during grain fill and lengthened the rain fill period. Cooler than average night temperatures can also mitigate water stress and slow the development of foliar diseases and insect problems.