Assessing The Risk of Frost Injury to Late Planted Corn

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.

Table 1

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.

 

 

Region

Median Frost Date

(50% probability)

Estimated GDDs Remaining

From Aug. 19 to Fall Frost

Northwest Oct 10 – Oct 20 673 – 723
North Central Oct 10 – Oct 25 656 – 741
Northeast Sept 30 – Oct 25 603 – 749
West Central Oct 10 – Oct 15 716 – 773
Central Oct 5 – Oct 15 670 – 796
East Central Sept 30 – Oct 15 645 – 763
Southwest Oct 10 – Oct 15 752 – 815
South Central Oct 15 – Oct 20 841 – 893
Southeast Oct 5 – Oct 15 651 – 774

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.

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.  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

Hot Night Temperatures Can Decrease Corn Yield

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.

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

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.

 

 

Corn Growth & Development – R1 Silking

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. 

 

R1 – Silking

Plants defined as Rl must have one or more silks extending outside the husk leaves.  This occurs about 55 to 66 days after emergence. Silks grow about 1 to 1.5 inches per day. Plants are at maximum or near maximum height and have near maximum vegetative dry matter.  Silking (Rl) is the only reproductive stage defined not on the characteristics of individual kernels. Determining the reproductive stage of the crop at and after Rl is based solely on the development of the primary ear.

The silking period is the most sensitive period for the crop; stress at this time can reduce kernel number per ear. Silks on the primary ear must be present while pollen shed occurs for successful pollination and fertilization. Synchronization between pollen shed and silking is important for obtaining high grain yields.

During Rl, both pollination and fertilization occur. Each silk is attached to one potential kernel. A pollen grain can land anywhere on an exposed silk and may germinate leading to fertilization. Silks remain receptive to pollen for a minimum of five days after they emerge.  The first silks to emerge from the husk leaves are those attached to potential kernels near the base (butt) of the ear. Silks attached to potential kernels at the ear tip are last to emerge and may not be pollinated if pollen shed has ended. Some potential kernels will simply not develop into harvestable kernels due to a failure in pollination or fertilization; these kernels will be visible on the ear as small, undeveloped white mounds.  As the plant approaches R2, kernels expand and have angled sides and a flatter top.

At Rl, the ear is at the beginning of a rapid elongation period and is only 40 to 45% of its final length.  Potassium uptake is essentially complete and nitrogen and phosphorus uptake is rapid in the plant. Nutrient content by leaf analysis is highly related to the final grain yield at this time. A response to previously applied fertilizer can be seen.

Management/Scouting: Scout for drought symptoms, Insects: Corn Earworm, Corn Rootworm adults,  and Japanese Beetles Diseases: Eyespot, Gray Leaf Spot, Norther Leaf Blight, Southern Leaf Blight and Tar Spot

 

Drought and Heat Stress

Source: Dr. Peter Thomison

Drought stressed corn near tassel emergence

One of the corn production scenarios agronomists least like is an exceptionally wet spring followed by a hotter and drier than normal July and August. The spring of 2019 was one the wettest on records throughout much of the state and now, as the dry weather that started in July persists, such a scenario seems to be a possibility in many Ohio corn fields. A combination of warm temperatures and inadequate rainfall is beginning to stress corn fields across Ohio. What’s exacerbating this problem are the marginal roots evident in some corn fields. Several factors, including poor planting conditions, surface/sidewall compaction and/or excessively wet soil conditions in June have inhibited good root development in many fields. With the onset of drier, warmer conditions in July, these small, shallow root systems have been unable to extract water deeper in the soil profile. Cooler weather and the possibility of storms later in the week may ease drought stress, which is important because many late planted corn fields (planted throughout June) are near or entering the pollination period, the stage of development most susceptible to drought. Other fields past pollination are vulnerable to kernel abortion, which drought conditions increase.

Corn is at many different stages of development because of the wide range in planting dates. To estimate the impact of dry hot weather on corn yield potential, let us review the effects of moisture deficits on corn growth and development from the late vegetative stages, prior to pollination, to the dent stage of kernel development. Yield losses to moisture stress can be directly related to the number of days that the crop shows stress symptoms during different growth periods. The following summarizes findings of past Iowa work that shows the potential impact of water stress on yield potential. Continue reading

Grain Fill Stages in Corn

Source:

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. 

Grain Fill Stages

The grain fill period begins with successful pollination and initiation of kernel development, and ends approximately 60 days later when the kernels are physiologically mature.  During grain fill the plant will do all it can to “pump” dry matter into the kernels, sometimes at the expense of the health and maintenance of other plant parts including the roots and lower stalk.

Kernel Development. The embryo and non-embryo sides of each kernel.

Cross-section of primary ears from R1 to R6. The embryo and non-embryo sides of each ear are shown once they are distinguishable.

 

A stress-free grain fill period can maximize the yield potential of a crop, while severe stress during grain fill can cause kernel abortion or lightweight grain and encourage the development of stalk rot (see table 1). The health of the upper leaf canopy is particularly important for achieving maximum grain filling capacity. Some research indicates that the upper leaf canopy, from the ear leaf to the uppermost leaf, is responsible for no less than 60% of the photosynthate necessary for filling the grain.

 

Table 2 shows the average amount of water needed for each growth stage and the cumulative total for the entire growing season.

 

Are Crops Catching Up?

Source: Peter Thomison, Laura Lindsey, OSU Extnesion

Corn –  Crop development varies tremendously across Ohio because of planting dates that range from late April to early July. According to field agronomists in some areas of the state, it looks like late-planted crops are “ rushing through development” …Unlike soybean, corn development is directly related to temperature, i.e. heat unit accumulation. Above average July temperatures (especially nighttime temperatures) have promoted rapid corn growth and development. After corn reaches the V10 stage (and most of our June plantings are near or beyond this stage), leaf collar emergence occurs at approximately one leaf every 50 GDDs.  See Corn Growth & Development posts on this blog for more detailed information on various corn growth stages.

Late planted corn fields (especially those that have adequate soil moisture and good soil fertility and weed control) may appear to be “catching up” with neighboring fields planted earlier. The rapid growth of late planted corn is associated with greater vegetative growth and faster canopy closure, which will help optimize yields. However, it does not mean that the rate of development of later plantings is greater than earlier plantings.  Corn growth and development have distinct meanings (Abendroth et al., 2011). Growth refers to the increase in size of an individual plant (or plant component) whereas development refers to a plant’s progression from earlier to later stages of maturity based on specific criteria (e.g., numbers of leaf collars).  So, while late planted corn may appear to be “catching up in terms” in terms of vegetative growth, i.e. plant height (probably because of longer internodes), it’s not caught up from the standpoint of development (leaf collar stages).

Corn plants can “adjust” their development in response to a shortened growing season. As was noted in a recent C.O.R.N. newsletter article (https://agcrops.osu.edu/newsletter/corn-newsletter/2019-12/will-planting…), a hybrid planted after late May will mature at a faster thermal rate (i.e. require fewer heat units) than the same hybrid planted in late April or early May. One of the consequences of delayed planting is that thermal time (GDD accumulation) from the dent stage (R5) to “black layer” or physiological maturity (R6) is shortened, “though this may simply reflect a premature maturation of the grain caused by the cumulative effects of shorter daylengths and cooler days in early fall or by outright death of the plants by a killing fall freeze” (Nielsen, 2018). Moreover, instead of a grain moisture content of about 30% at black layer, typical for normal planting dates, grain moisture at black layer for late plantings may be as high as 40%, which may require longer field drying and harvest delays.

Soybeans – Continue reading

Expect cornfields pollinating well into August

Source: Dr. Peter Thomison, OSU Extension

According to the National Agricultural Statistics Service for the week ending July 28, 2019, 32% of the state’s corn was silking compared to 75% for the 5-year average. Given the wide range in corn planting dates this year, most corn will not achieve tasselling and silking until we are well into August. The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination. Stress conditions (such as hail damage and drought) have the greatest impact on yield potential during the reproductive stage. The following are key steps in the corn pollination process.

Most corn hybrids tassel and silk about the same time although some variability exists among hybrids and environments. On a typical midsummer day, peak pollen shed occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon. Pollen may be shed before the tassel fully emerges. Pollen shed begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen. Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels (see figure). Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet.

Continue reading

Corn Growth & Development – VT – Tasseling

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.  

 

VT – Tasseling 

  • Approximately 1250 Growing Degree Days (GDD’s)
  • Tasseling and kernel fertilization are arguably two of the more critical stages.

The VT stage occurs when the last branch of the tassel is completely visible, extended outward, and not held in by the upper leaves. The plant is nearly at its full height. Most hybrids grown in the Corn Belt will have a total of 19 to 20 leaves prior to tassel. VT begins about 2 to 3 days before silk emergence.

Although the tassel is an easy structure to identify for staging purposes, the occurrence of pollen shed is more important. The shedding of pollen is a determining factor in whether or not silks become pollinated and potential kernels fertilized.

All branches of the tassel may not be fully extended above the upper leaves before the anthers on the main branch start shedding pollen. Also, silks will often be visible before the tassel is fully extended above the upper leaves; if this occurs the plant should be defined as Rl despite VT not technically occurring first. The interval between VT and R1 can fluctuate considerably depending on the hybrid and the environment. Drought stress lengthens this interval.  The plant is extremely vulnerable to hail from VT through silking (R1)

The length of the pollination window differs based on whether it is for the whole field or for an individual plant. Plants within a field do not all begin or end pollen shed at the same time due to plant variability. Most fields will have pollen shed occurring for seven or more days. However, the greatest production of pollen from that field exists for a shorter time period of approximately four days. An individual plant at peak pollen production can release .5 million or more pollen grains per day.

Management/Scouting: Scout for Insects: Corn Earworm, Corn Rootworm, European Corn Borer and Japanese Beetles and Western Bean Cutworm.  Diseases: Eyespot, Gray Leaf Spot, Norther Leaf Blight, Southern Leaf Blight and Tar Spot