Pre-Pollination Updates--Let's Talk Weather  06/21/18 10:29:28 AM

Corn Development--The continued above normal temperatures and abundant moisture this week will certainly continue a rapid growth phase in the coming weeks.  Much of the early planted corn (This example was planted April 25th) is at or approaching the 12 leaf to 15 leaf stage V12--V15 and although the ear shoots (potential ears) were formed just prior to tassel formation (V5) the number of ovules (potential kernels) on each ear and the size of the ear are now being determined.  You can find this process by cutting the developing ear shoot in half and see the developing ear now.  

DeKalb DKC51-19 (101 RM) planted 4/25/18—Photo taken 6/20/2018
Tassel emergence—Soon to begin    Silks Development—Longest Silks (first       
 Pollination                                          out of the husk)
will fertilize the         
                                                               kernels on the base of the cob

Let’s talk weather!!  Below is a summary of the temperatures, rainfall, etc. from our weather station here at WBI.  I have included the April, May and June (so far) summaries.  Many times we forget what the crop has/has not endured since we planted it back in April.
Consider this:  Corn planted April 25th—(personal optimum planting date) acquired 75 GDD and 0.04 inches of rain in April since planting—Not much—also consider there were only 184 GDD’s for the entire month.
Observed at: Wiles Bros. Inc. (DI4759)
  • Highest Temperature: (°F) 86.0
  • Lowest Temperature: (°F) 14.0
  • Average Temperature: (°F) 45.2
  • Depart. From Normal: (°F) -
  • Evapotranspiration: (in.) 4.06
  • Growing Degree Days: 184
  • Corn Heat Units: 244
  • Total Precipitation: (in.) 0.68
  • Total Snow Fall: (in.) 4.18
  • Normal Precipitation: (in.)
    Now let’s look at May
    Observed at: Wiles Bros. Inc. (DI4759)
  • Highest Temperature: (°F) 100.0
  • Lowest Temperature: (°F) 48.0
  • Average Temperature: (°F) 70.9
  • Depart. From Normal: (°F) -
  • Evapotranspiration: (in.) 6.18
  •  Growing Degree Days: 618
  • Corn Heat Units: 763
  • Total Precipitation: (in.) 3.82
  • Total Snow Fall: (in.) 0.00
  • Normal Precipitation: (i
    And June (So Far)
    Observed at: Wiles Bros. Inc. (DI4759)
  • Highest Temperature: (°F) 96.0
  • Lowest Temperature: (°F) 56.0
  • Average Temperature: (°F) 77.3
  • Depart. From Normal: (°F) -
  • Evapotranspiration: (in.) 4.85
  • Growing Degree Days: 506
  • Corn Heat Units: 579
  • Total Precipitation: (in.) 8.51
  • Total Snow Fall: (in.) 0.00
  • Normal Precipitation: (in.) -
    So, to date, corn planted on April 25th (Example Above) has accumulated 1149 GDD. And as expected with that amount of GDD’s , it at pre-tassel.  You will notice that the weather station also monitors Corn Heat units and that they are different than the historic GDD scale.  Must all corn hybrids are rated on the GDD scale to maturity so we will use that one for our discussion.  With this many GDD’s from April 25th you will be able to find the tassel deep within the whorl and it will likely emerge in this next week or so.  Given that April was SOOO COLD and now we are really ahead by about 10 calendar days, it is a true testament to how warm/hot May and June have been.

    RAINFALL has been spotty at best.  Here on the Eastern side of Cass Co., timely rainfall has occurred since corn planting without any hinderance on crop development. BUT, that is not the case everywhere.  This week’s rains have again been again, spotty, with some locations receiving over 8” this week while other areas have had a fraction of that.    Regardless of the amount—the rain is coming during a fairly crucial time in plant development.  The moisture has gone a long way to re-charge the soil moisture profile—it may not be enough dependent on how dry certain areas have been, but,  the cooler, wet, weather could not have come at a better agronomic time for corn.
    The corn will try to use up to 0.20" of moisture transpired through the plant on a daily basis, so the rains this week are coming at a good time.  The corn crop is currently acquiring between 25 and 30 GDD per day Plant injury (green snap) at this stage of development in corn is most damaging to yield due to the vulnerability of fast growing plants make stalks weaker at the internodes as well as the plant puts more energy towards the reproductive development phases of growth rather than structural support. 
    Growing Degree Days for Corn Growth Stages for a 113 day Hybrid
    Stage                              GDD (Growing Degree Days--base 50)       
    Emergence                                                            120
    2 leaf-V2                                                               215
    V6—tassel initiation                                             490
    V10                                                                      770
    V14                                                                      1025
    VT (tassel emergence)                                           1190
    Silking                                                                  1480
    R4 (Kernel dough stage)                                        1990
    R5 (Kernel dent stage)                                           2480
    R6 (physiological maturity—black layer)               2825
    *courtesy of Hollinger (University of Nebraska)


Growth Stage                          Inches Water Use/Day

1-4 leaf                                              .02 - .05
5-8 leaf                                              .05 - .10
8-10 leaf                                            .10 - .15
11-14 leaf                                          .15 - .20
14-18 leaf                                          .20 - .25
19 leaf - blister                                  .25 - .30
Milk - soft dough                               .20 - .25
Hard dough - early dent                      .15 - .20
Mid - full dent                                   .10 - .15
The Process of Pollination.  (the annual review)
Although a couple of weeks away yet for many fields, silking and pollen shed will begin to happen in some of the earlier planted corn and the next critical phase of development in the life of a corn plant that will impact yield potential and results at harvest. (See Example #1 below—Corn Planted April 25th, 2018) 
Corn is a monoecious species meaning that both the male and female reproductive parts of the flower are present on the same plant.  The male part of the plant consists of the tassel, anthers and pollen. Each corn plant on average produces between two and five million spherical, yellowish-translucent pollen grains. Each of these yellow 'dust-like' pollen grains contains the male genetic material necessary for fertilizing the ovary of one potential kernel. If we multiply plants per acre by potential pollen grains per plant the number of pollen grains produced within a field of corn is astronomical.  In general, it takes approximately 7 days for an individual tassel to finish shedding its pollen, although the majority of pollen may be shed during the second and third day of anther emergence. Due to variance within a field, it may take as long as 14 days for a field to complete pollen shed. Pollen is not shed when anthers are wet. Cool, cloudy, humid conditions also delay the onset of pollen shed. Extreme heat stress (100 F or greater) can kill corn pollen, but since pollen maturation and shed is spread out over a period of time ranging from several days to two weeks at least a portion of the pollen in the field will avoid the temperatures, mature, be shed and fertilize the ovules on the ear.
The silks are the functional stigmas of the female flowers. Every potential kernel (ovule) on an ear develops its own silk that must be pollinated in order for the ovary to be fertilized and develop into a kernel. Though we typically harvest only 400 to 600 actual kernels per ear, up to 1000 ovules develop on each ear.
Silk elongation begins 7 to 10 days prior to silk emergence from the husk. Complete silk emergence from an ear generally occurs within two to seven days. Typically, silks from the basal portion of the ear emerge first, while the tip silks generally emerge last. Silks remain receptive to pollen (and fertilization) for up to 10 days.
In order for a kernel to develop, pollen must be transferred to the silk (pollination) and the male gametes must make their way down the silk to combine with the female gametes in the ovule (fertilization). Successful pollination does not necessarily equal successful fertilization and kernel formation. Pollen grains can germinate anywhere along a length of exposed, receptive silk and many pollen grains will germinate and initiate a pollen tube but generally only one will fertilize the ovary.
Silk clipping by certain insects like the corn rootworm beetle not only removes viable silk tissue, but also injures a certain length of the remaining silk. Generally, silk length on these injured ear shoots must be at least 1/2 inch to ensure that a sufficient length of uninjured silk tissue is exposed for pollen germination to occur.  Less than ideal environmental conditions can delay flower development and pollination or result in variable flowering dates. The consequences of delayed or variable flowering dates are 1) the increased risk of poor or uneven kernel set due to insect or weather stress during the later flowering period and 2) greater variability in grain maturation within a field and the subsequent grain moisture at harvest. The greater risk of insect or weather stress during later flowering is due to the attraction of certain insects (example--Corn Rootworm) to late flowering corn.
Soybean Development---Many soybean fields are between the V3 and V5 (third to fifth nodes).  Not much is said about soybean development during the reproductive stages maybe because it is not as flashy as corn is during this stage.  Although not as visible as corn, soybeans are now beginning to bloom, and visible pod set and fill are not far away.  We have visited about the triggering mechanisms for soybeans to begin to bloom.  Soybean blooming is normally triggered around the first day of summer—TODAY  June 21st

Asgrow AG36X6 planted 5/5/2018—Taken 6/20/2018
Physical stress to the plant from herbicide applications, water stress, physical injury from hail, etc. all play a larger role now than any other time of plant development in yield determination. Dependent on variety, a soybean plant has the ability to produce enough blooms to produce yields up to 250 bushels but, 75% typically abort. During the reproductive stage, a soybean plant (much like corn) will require an average of 0.25 inches of water per day.  If we can eliminate any moisture stress during the critical pod set, via timely rains in late July and August, the percent of pods aborted will decrease.
The soybean flower is self-pollinated which means that the pollen produced within a flower fertilizes the ovary (egg—pod) of that same flower.  Unlike corn pollination, studies have shown that little if any cross-pollination occurs in a soybean field   Soybean flowers are often fertilized by the time they are visibly open and few pods are set by the first flowers.  Flowering and pod set can last for up to six weeks, however, the majority occurs in a three week time frame which will begin in about 2 weeks.


Growth Stage                           Inches Water Use/Day
Germination/Emergence           .1 - .15
Vegetative Growth                   .15 - .20
Flowering                                .25 - .30
Pod Development                     .20 - .25
Seed Fill                                   .15 - .20
Maturation                               .05 - .10
John W. McNamara
Wiles Bros. Inc.
606 Wiles Road
Plattsmouth NE. 68048
(402) 298-8550--Office
(402) 499-3870--Cell
(402) 298-7174--Fax
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