1. Corn Growth and Development
Chad Lee
Grain Crops Extension Specialist ●
This is an introduction into corn growth and development.

2. Corn Growth Stages Vegetative (V) Reproductive (R)
How a Corn Plant Develops, Special Report No. 48
Iowa State University
Corn growth and development is divided into two major sections: vegetative and reproductive. There are several methods for determining vegetative stages, but we are going to focus on the leaf collar method or fully-extend leaf method. This method uses a defined, visible part of the plant to identify stages. The leaf collar is defined as the part of the leaf that connects the leaf to the sheath of the plant. The leaf collar resembles a an shirt collar with one button open around someone’s neck.

3. Corn Emergence (VE)
Emergence occurs when the plant shoot pokes through the soil surface. The radicle emerges from the seed and starts the seminal root system. The seminal root system will be the major root system of the corn plant until the plant reaches about V3. The coleoptyle emerges upward from the seed and contains five leaves of the plant. The mesocotyl extends from the coleoptyle until the shoot reaches the soil surface. Once the shoot reaches the soil surface the mesocotyl stops growing and the leaves begin to emerge. Cool temperatures and/or severe compaction can prevent the mesocotyl from growing straight up toward the soil surface.

4. Corn Growth Stages: Vegetative
3 Collars V6
6 collars
V12
12 collars
V15
15 collars VT
tassel
The vegetative stages begin at emergence (VE) and end at tassling (VT). We are going to focus on a few of the vegetative stages. The numbers following the V stage represent the number of collars that are visible.

5. V3 V6 V12 Corn Growth Stages 3 Collars 6 collars 12 collars
Nodal roots active.
Growing point below ground V6
6 collars
Growing point above ground.
Tassel and ear development starting.
V12
12 collars
Ear size, kernel size and kernel number being determined.
Limits on water and/or nutrients will reduce yields.
V3 occurs when 3 leaf collars are visible on the stalk of the plant. V3 means that 3 nodes have fully developed in the plant. At this stage, roots have formed from the first node and these roots will become more important than the seminal root system at collecting water and nutrients and providing structural support to the plant. Nodal roots will eventually form at about the first six or seven nodes. The growing point is still below ground at the V3 stage, making the plant fairly tolerant of freezes. If all of the above-ground growth is removed and no damage is done to the growing point below ground, the plant will regrow a shoot and have minimal yield losses . . .as long as growing conditions are favorable.
By V6, or six collars, the growing point is above ground and removal of all the above-ground growth will likely kill the entire plant. Tassel and ear development have started. Many post-emergence herbicides have restrictions against corn that is at the V6 growth stage. Applications of some herbicides directly on the corn plant at or after this stage of growth will damage the developing ears.
At or shortly after V6, the corn stalk will expand and start to tear off older leaves and collars. The stalk of the corn plant may need to be split in two to identify the number of fully developed nodes.
V12 has 12 fully developed nodes or collars. Ear size, kernel size and kernel number are being determined. Any limits on water or nutrients at this stage will reduce yields. The level of yield reduction depends on the intensity and duration of the stress. For example, a mild limit to water will hurt yields very little, but a severe drought will hurt yields by 10 to 15%, if growing conditions following this stage are favorable.

6. V15 VT Corn Growth Stages 15 collars tassel
Rapid growth, about 10 to 12 days before silking.
Most sensitive to stress. VT
tassel
Last tassel branch is visible but prior to silking.
Complete leaf loss will cause nearly 100% yield loss.
When the plant reaches V15

7. Corn Growth Stages Comparing visible collars to actual nodes.
Tassel and ear development start early.

8. Corn Growth Stages: Reproductive
Silking R2
Blister R4
Dough R5
Dent R6
Physiological Maturity

9. R1 R2 Silking Blister Corn Growth Stages N and P uptake are rapid.
About 50% of total N is taken up after R1.
K uptake is nearly complete.
Water needed for pollination.
Pollination occurs. R2
Blister
Ear size nearly complete.
Silks begin to dry out.
A miniature corn plant is being formed in each fertilized kernel.

10. R4 R5 Dough Dent Corn Growth Stages
Kernels have accumulated ½ of total dry weight.
Five leaves have formed in the kernel. R5
Dent
Most kernels have dented and are near 55% moisture at start.
Starch layer has formed and progresses down the kernel.

11. R6 Corn Growth Stages Blacklayer has formed at bottom of kernel.
Physiological Maturity
Blacklayer has formed at bottom of kernel.
Kernel is about 30 to 35% moisture.

12. Corn Growing Degree Days
Each day has a slightly different average temperature.
Temperature affects corn growth rate.
Attempt to relate temperature to corn growth rate.
Corn Growing Degree Day
Base 50° F
Max 86° F
Min 50° F

13. Corn Growing Degree Days
Base 50° F
Max 86° F
Min 50° F
Example 1:
74° F average daily temperature
74 – 50 = 24 GDD
Example 2:
90° F average daily temperature
86 – 50 = 36 GDD

14. Corn Growing Degree Days
Corn Maturity (Days)
GDD
85 to 100
2100 – 2400
101 to 130
2400 – 2800
131 to 145
2900 – 3200
GDD Requirements of a 2700 GDD Hybrid
Growth Stage
GDD V2
200 V6
475
V12
870 VT
1135 R1
1400 R6
2700
From NCH-40 Growing Season Characteristics and Requirements in the Corn Belt. National Corn Handbook.

15. Planting Date and GDD April 20 1155 --- May 3 1029 126 May 18 825 330
Hybrid: DKC67-91: 119 CRM
3000 GDD to Black Layer
Planting Date
GDD
As of 06/26/05
Difference From First Planting
April 20
1155
---
May 3
1029
126
May 18
825
330
May 31
596
559
June 15
281
874
From University of Kentucky Ag Weather Center:
Growing Degree Day calculator:

16. Planting Date and GDD April 20 1503 --- May 3 1377 126 May 18 1173 330
Hybrid: DKC67-91: 119 CRM
3000 GDD to Black Layer
Planting Date
GDD
As of 07/11/05
Difference from First Planting
April 20
1503
---
May 3
1377
126
May 18
1173
330
May 31
944
559
June 15
629
874
From University of Kentucky Ag Weather Center:
Growing Degree Day calculator:

17. Corn Ears: Good and Bad 1

18. Corn Ears: Good and Bad 1 2

19. Corn Ears: Good and Bad 1 3