Corn Development

Originally written February 1, 2006 | Last updated February 03, 2014

The corn plant is one of nature's most amazing energy storing devices. It does this by producing a large efficient energy "factory" - the plant with its roots, leaves, stalk, and flowering parts - and then by capturing the sun's energy and storing large amounts of this energy in the grain, in a chemical form (largely starch) that can be used as an energy source by animals.

Nature provides the major portion of the environmental influence on corn growth and yields. However, the corn producer can manipulate the environment with managerial operations including hybrid selection, soil tillage, crop rotation, soil fertilization, irrigation, and pest control. A producer who understands the growth and development of corn can use production practices to obtain higher yields and profit by being more efficient and timely.  

 A producer who understands the corn plant can use production practices more efficiently and timely to obtain higher yields and profits.  

Corn Growth and Development Staging Systems
VE
V6
V12
V18
R1: Silking
R6: Physiological maturity
Factors affecting corn growth and development

Identifying Stages of Development  

  How a corn plant develops - Iowa State University Special Report No. 48

Corn Growth and Development & Management Information for Replant Decisions  University of Minnesota FO-5700-GO

Maize Growth and Development  University of Illinois  

The staging system most commonly used is the Iowa System. It divides plant development into vegetative (V) and reproductive (R) stages (Table 1.). Subdivisions of the V stages are designated numerically as V1, V2, V3, through Vn, where n represents the last stage before VT (tasseling). The six subdivisions of the reproductive stages are designated numerically.  

Vegetative Stages Reproductive stages
  VE  Emergence
  V1  First leaf collar
  V2 Second leaf collar
  V3  Third leaf collar
   .
   .
   .
  VT  Tasseling  
  R1  Silking
  R2  Blister
  R3  Milk
  R4  Dough
  R5  Dent
  R6  Black layer (Physiological maturity)  

 Each leaf stage is defined according to the uppermost leaf whose collar is visible.  

 Beginning at about V6, increasing stalk and nodal root growth combine to tear the small lowest leaves from the plant. To determine the leaf stage after lower leaf loss, split the lower stalk lengthwise and inspect for internode elongation. The first node above the first elongated stalk internode generally is the fifth leaf node. The internode usually is about one centimeter in length. This fifth leaf node may be used as a replacement reference point for counting to the top leaf collar.  

 In a corn field all plants will not be in the same stage at the same time. Each specific V or R stage is defined only when 50% or more of the plants in the filed are in or beyond that stage.  

 Although each stage of development is critical for proper corn production we will focus on VE, V6, V12, V18, R1, and R6. Table 2 describes the yield components being determined at each growth stage.  

Corn growth and development stages when yield components are determined
Growth
Stage
  Yield components
GDU Potential Actual
VE 125 Ears/area -----
V6 470 Kernel rows/ear "Factory"
V12 815 ----- Kernel rows/ear
V18 1160 Kernels/row -----
R1 1250 Kernel weight Kernel number Ears/area
R6 2350 ----- Kernel weight

Much of the  following is a synopsis of the publication entitled "How a corn plant develops" (Iowa State University Special Report No. 48)

Corn is perhaps the most completely domesticated of all field crops. Its perpetuation for centuries has depended wholly upon the care of man. It cannot exist as a wild plant. The greatest plant-breeding job in the world was done by the Native Americans. They developed types of corn adapted to so wide a range of climates that this plant is now more extensively distributed over the earth than any other cereal crop. One of the neat things about agriculture is the changing of the seasons. The fact that plants grow uniformly within a field during a cropping season, ripen synchronously, and are harvested at about the same time is truly amazing.

The synchrony of development between and within plants is largely taken for granted by farmers. Yet synchrony allows a grower to spray herbicides, irrigate and most importantly harvest in a single operation. Synchrony is a remarkable feat of coordination by the plants. Days or weeks may elapse between tiller, spikelet, or floret initiation, and yet they flower at about the same time and grains ripen simultaneously within the span of a few days. The observed synchrony of crop development cannot be achieved without coordinated responses of a number of developmental processes (e.g. Leaf and ear development) to the environment. How this coordination between plant and environment is achieved is largely unknown in spite of widespread use of plant growth regulators. Current understanding of the molecular aspects of the control of plant development are poor at best.

We will concentrate on an early to mid-season (90 to 100 day) hybrid for Wisconsin. Each plant typically develops about 20-21 total leaves, silks about 65 days after emergence, and matures about 120 days after emergence. All normal corn plants follow this same general pattern of development, but the specific time interval between stages and total leaf numbers developed may vary between different hybrids, seasons, planting dates and locations. An early maturing hybrid may develop fewer leaves or progress through different stages at a faster rate than indicated here. A late maturing hybrid may develop more leaves or progress more slowly than indicated here. The rate of plant development for any hybrid is directly related to temperature, so the length of time between the different stages will vary as the temperature varies, both between and within growing seasons. Environmental stress such as nutrient or moisture deficiencies may lengthen the time between vegetative stages but shorten the time between reproductive stages. The number of kernels that develop, final kernel size, rate of increase in kernel weight, and length of reproductive growth period will vary between different hybrids and environmental conditions.

Thermal Time and Crop Management

Producer Benchmarks

  1.   "Plant corn when oak leaves are as big as a squirrel's ear."
  2.   "Plant corn when you can drop your drawers and sit on the ground for two minutes under a full moon."
  3.   "Knee-high by the Fourth of July."
  4.   "Pollinated by August, dented by Labor Day."
  5.   "Corn will dry down right when frost doesn't occur until after the first full moon in September."
  6.   "Harvest when 8 of 10 ears float in a stock tank."

Growing Degree Units (GDU) = ( ( Tmax + Tmin ) / 2 ) - Tbase

where

Tmax = maximum daily temperature (upper limit = 86 F).   Tmin = minimum daily temperature (lower limit = 50 F).   Tbase = base or threshold temperature for corn growth.

Daily range = 0 to 36 GDU

Minimum and maximum temperatures for crop and pest management  
models (Pope, IC-492(8) p. 46, May 17, 2004).
Crop or Pest Minimum oF Maximum oF Information Use
Corn 50 86 crop development
Soybean 50 86-90 crop development
Black cutworm 50   300 DD from egg to cutting
Stalk borer 41   predicting migration
Bean leaf bettle 46   2nd generation emergence
Seedcorn maggot 39   seed treatment on replant
Alfalfa weevil 48   larval presence in fields
Western bean cutworm 50   adult emergence / egglaying

Growing Degree Units in Wisconsin

     

Average growing degree unit accumulation for corn planted on
May 1 in the southern production zone of Wisconsin.
Date Rate Accumulative
  GDU per day total GDU from May 1
May 1 -- 0
May 11 10 100
June 15 14 600
June 30 20 900
July 15 20 1200
July 31 22 1550
August 15 23 1900
August 31 19 2200
September 15 13 2400
September 30 13 2600
derived from Mitchell and Larsen, 1981   Range in growing degree day
accumulation for corn planted on   May 1 in southern Wisconsin.

 

Average growing degree unit accumulation for corn planted on
May 1 in the southern production zone of Wisconsin.
Date Average Range
Jun 30 900 800-1000
Jul 31 1550 1450-1650
Aug 31 2200 2100-2300
Sep 30 2600 2500-2700
derived from Mitchell and Larsen, 1981 Range = expectation that any
particular year is greater than or less than normal once in five years.

Factors affecting corn growth and development

  1. Conservation tillage
  2. Soil texture
  3. Planting date
  4. Seed-zone soil moisture
  5. Seed-bed condition
  6. Seeding depth
  7. Severe drought or heat stress
  8. Hybrid differences for development

Corn plants increase in weight slowly early in the growing season. But as more leaves are exposed to sunlight, the rate of dry matter accumulation gradually increases. Cell division in the leaves occurs at the growing tip of the stem. Leaves enlarge, become green, and increase in dry weight as they emerge from the whorl and are exposed to light. The leaves of the plant are produced first, followed by the leaf sheaths, stalk, husks, ear shank, silks, cob and finally grain. By V10, enough leaves are exposed to sunlight so the rate of dry matter accumulation is rapid. Under favorable conditions, this rapid rate of dry matter accumulation in above-ground plant parts will continue at a nearly constant daily rate until near maturity. Highest yields will be obtained only where environmental conditions are favorable at all stages of growth. Unfavorable conditions in early growth stages may limit the size of the leaves (the photosynthetic factory). In later stages, unfavorable conditions may reduce the number of silks produced, result in poor pollination of the ovules and restrict the number of kernels that develop; or growth may stop prematurely and restrict the size of the kernels produced.

Stage VE: Determination of potential ear density  

 Approximately 7-10 days after planting (125 GDD)  

 Aboveground

  • Coleoptile tip emerges above soil surface
  • 1st true leaves rupture from the coleoptile tip
  • Elongation of coleoptile ceases

 Belowground

  • Mesocotyl and coleoptile elongation
  • Elongation of mesocotyl ceases
  • Growing point is below the soil surface
  • Completed growth of seminal root system (radicle + seminal roots)  
    • Seminal root system supplies water and nutrients to developing seedling
  • Nodal roots are initiated
    • Nodal roots are secondary roots that arise from belowground nodes.

Troubleshooting  

  • Watch for seed attacking insects: wireworm, white grub, seed corn maggot, seed corn beetle (table 3)
  • Germination and emergence delayed when inadequate moisture
  • In cool soil banding small amounts of starter fertilizer to the side and slightly below the seed can improve early vigor, especially when soils are cool.
  • If conservation tillage is implemented add 30-60 GDU to VE time
  • If planting date is before April 25 then add 10-25 GDD, while if after May 15 subtract 50-70 GDD
  • For deeper seeding depths, add 15 GDU for each inch below 2 inches
  • Seed-bed condition: soil crusting or massive clods add 30 GDU
  • Seed-zone soil moisture: below optimum, add 30 GDD

Stage V6: Potential plant parts ("factory") developed and Potential Kernel rows being determined

24-30 days after emergence (475 GDD)

Aboveground

  • Growing point and tassel (differentiated in V5) are above the soil surface
  • Stalk is beginning a period of rapid elongation
  • Determination of kernel rows per ear begins Strongly determined by a hybrid's genetics
  • Tillers (suckers) are visible at this time
  • Degeneration and loss of lower to leaves
  • New leaf emerging (V-stage) about every 3 days

Belowground

  • Nodal root system is established (18" deep X 15" wide) This is now the main functional root system of the plant

Troubleshooting:

  • Lodged plants Rootworm eggs have hatched and larvae are feeding on root systems
  • Foliar defoliation from hail ,wind, and leaf feeding corn borers May decrease row number
  • 100% yield loss to frost caused from plant death
  • 53% yield loss to hail when completely defoliated
  • Severe yield loss to flooding

Management Guide

  • Time to apply nitrogen (up to V8) before rapid uptake period in corn
  • Precise fertilizer placement is less critical
  • Banding small amounts of starter fertilizer to the side and slightly below the seed can improve early vigor, especially when soils are cool.
  • If conservation tillage is implemented add 30-60 GDU to VE time
  • If planting date is d 15 GDU for each inch below 2 inches
  • Seed-bed condition: soil crusting or massive clods add 30 GDU
  • Seed-zone soil moisture: below optimum, add 30 GDD

Stage V12: Actual Kernel rows determined

42-46 days after emergence (815 GDD)

Aboveground

  • Number of kernel rows is set
  • Number of ovules (potential kernels) on each ear and size of ear is being determined
    • Strongly affected by environmental stresses
  • New V-stage approximately every 2 days

Belowground

  • Brace root formation begins
  • Brace roots stabilize the upper part of the plant and additional weight of the tassel and ears.

Troubleshooting

  • Moisture Deficiencies will reduce potential number of kernels and ear size
  • Plant is utilizing 0.25 inches/day (Table 4.)
  • Nutrient Deficiencies, will reduce potential number of kernels and ear size
  • Major amounts of nitrogen, phosphorous, and potassium are being utilized at this stage
  • Lodged plants at this stage will also decrease yields 2-6%
  • 100% yield loss to frost caused from plant death
  • 81% yield loss to hail when completely defoliated
  • 3%/day yield loss to drought or heat
  • Flooding (< 48 h) will usually not affect yield, unless N leaching occurs

Management Guide

  • Potential of kernel number and ear size is also related to the length of time available for their determination
  • Early hybrids- progress faster through growth stages and usually have smaller ears than late hybrids (May want to think about this when determining plant densities)

Stage V18: Potential kernels per row being determined

56 days after emergence (1160 GDD)

Aboveground

  • How many rows and kernels per row are still being determined
  • Ear development is rapid
  • The upper ear shoot is developing faster than other shoots on the stalk
  • One week from silking

Belowground

  • Brace roots are now growing from nodes above the soil surface They will scavenge the upper soil layers for water and nutrients during reproductive stages

Troubleshooting

  • Moisture deficiency will cause lag between pollen shed and beginning silk ("nick")
  • Largest yield reductions will result from this stress
  • Plant using 0.30 inches per day
  • Lodging will cause 12-31% yield reduction
  • 100% yield loss to frost (< 28 F) caused from plant death
  • 100% yield loss to hail (max) when completely defoliated
  • 4% yield loss per day due to drought or heat
  • Flooding (< 48 h) will not affect yield, unless significant N leaching occurs

Management Guide

  • Nitrogen applied through irrigation water, should be applied by V18

Stage R1: Actual kernel number and potential kernel size being determined

69-75 days after emergence (1250 GDD)

Figure. Typical kernel development in Wisconsin.

Aboveground

  • Begins when any silks are visible outside the husks
  • Pollen shed begins and lasts 5-8 days per individual plant
  • Silk emergence takes 5 days
  • Silks elongate from base of ear to tip of ear
  • Silks elongate until pollinated
  • Silks outside husks turn brown
  • The plant has now reached its maximum height
  • First 7-10 days after fertilization cell division occurs within kernel
  • Remaining R stages, endosperm cells fill with starch

Belowground

  • The plant must have a healthy root system because proper uptake if moisture and nutrients are critical at this time

 Troubleshooting

  • Hot and Dry weather results in poor pollination and seed set
  • Dehydrates silks (delay silking) and hastens pollen shed
  • Causes plants to miss windoStresses that reduce pollination result in a "nubbin" (an ear with a barren tip)

Stage R6: Actual kernel weight determined

130 days after emergence or 50-60 days after silking (2350 GDD)

Aboveground

  • Physiological maturity is reached when all kernels on the ear have attained their maximum dry matter accumulation
  • The hard starch layer has advanced completely to the cob
  • Goes from top of kernel to base of cob
  • A black abscission layer has formed
  • This indicates that moisture and nutrient transport from the plant has ceased
  • Kernels are at 30-35% moisture and have attained 100% of dry weight

Management Guide

  • Grain is not ready for safe storage
  • Costly to harvest at R6
  • Needs to be at 13-15% moisture for long-term storage
  • May be advantageous to let crop partially dry in the field
  • Silage harvest would be slightly earlier than R6 as milkline moves down towards kernel tip
  • Frost has no affect on yield at this point. However, lodging from disease, insect damage or hybrid can result in physical loss of yield.
Relationship between kernel growth stage and development.
      Percent of Maximum Yield Moisture Content
Stage Calendar days to
maturity (average)
Growing degree units
(GDUs to maturity)
Grain Whole plant Grain Whole Plant
Silk  (R1) 55-60 1100-1200 0 50-55 -- 80-85
Blister (R2) 45-50 875-975 0-10 55-60 85-95 80-85
Late milk-dough (R4) 35-40 650-750 30-50 65-75 60-80 75-80
Early Dent (R5) 25-30 425-525 60-75 75-85 50-55 70-75
Fully Dented (5.50-5.75) 13-17 200-300 90-95 100 35-40 65-70
Physiological maturity (R6) * 0 0 100 95-100 25-35 55-65
* Black layer formation and/or milk disappearance  from kernels under development. Premature frost or extended cold temperatures may cause black layer formation at earlier stages and wetter moistures.

Conclusions

For most of Wisconsin hybrids (~100 day), each plant typically develops 20-21 leaves, silks about 65 days after emergence, and matures about 120 days after emergence. All normal plants follow this same general pattern of development, but specific time intervals between stages and total leaf numbers developed may vary between different hybrids, seasons, planting dates and locations. The rate of plant development for any hybrid is directly related to temperature, so the length of time between the different stages will vary as the temperature varies. Environmental stress may lengthen or shorten the time between vegetative and reproductive stages.

The length of time required for the yield components of ear density, kernel number, kernel weight varies between hybrids and environmental conditions (Fig. 1.). The yield triangle once again emphasizes the important yield components of corn. One of the important aspects that should be recognized is the earliness at which yield is actually determined. It is true that yield is the end product but a numbers of stages are required to produce yield. This won't necessarily put "money in your pocket", but by knowing when yield components are determined helps us to interpret management and environmental factors influencing yield.

Factors affecting corn growth and development

  1. Conservation tillage: more than 75% residue, add 30-60 GDU (Swan et al., 1977; Imholte & Carter, 1987)
  2. Soil texture: fine = add 30-60 GDU; coarse = subtract 30-60 GDU
  3. Planting date: < April 25 = add 10-25 GDU; > May 15 subtract 50-70 GDU
  4. Seed-zone soil moisture: below optimum, add 30 GDU (Schneider and Gupta, 1985)
  5. Seed-bed condition: soil crusting or massive clods add 30 GDU (Schneider and Gupta, 1985)
  6. Seeding depth: add 15 GDU for each inch below 2 inches (Hunter and Kannenberg, 1972)
  7. Severe drought or heat stress
  8. Hybrid differences for development

Factors affecting yield

Yield components of corn = Ears per unit area X Kernel weight X Kernels per ear (Row number x Kernels per row)

Potential v. Actual Yield Components

  • Potential = maximum number or size; attrition always occurs.
  • Actual = result of growth process after attrition.

 

Required growing degree days and calendar date when development stage
is theoretically achieved for a corn hybrid of 95-105 RM when planted on
May 1 in southern Wisconsin.
Growth Stage Required Date
GDU Average Range
VE 125 May 12 May 10-14
V6 470 June 7 June 5-9
V12 815 June 26 June 22-29
V18 1160 July 13 July 9-18
R1 1250 July 17 July 13-20
R6 2350 Sep 11 Sep 4-19
Sources: Neild and Seeley, 1977; Swan et al., 1987; Schneider and Gupta, 1985;
Imholte and Carter, 1987; Bauer and Carter, 1984, Crookston et al.,   1982;
Mitchell and Larsen, 1981

 

Impact on grain yield (% yield loss) of various abiotic factors
occurring during corn development
Factor VE V6 V12 V18 R1 R6
Frost (< 28 F) 0 100 100 100 100 0
Hail (max) 0 53 81 100 100 0*
Drought/Heat (%/day) -- -- 3 4 7 0
Flooding (<48 h) severe 0 0 0 0
* No ear dropage

Further Reading

Darby, H., and J. Lauer. 2000. Critical Stages in the Life of a Corn Plant. UW Crop Scouting Manual. UWEX Publications, Madison, WI.


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