Growth Stages

Corn growth stages are divided into vegetative (V) and reproductive (R) growth stages. The vegetative growth stages start with the corn emergence and reproductive growth stages start with silking.

Vegetative (V) growth stages

The vegetative growth stages start with corn emergence (VE) and finish with tasseling (VT) (Table 1). During the VE stage, the mesocotyl elongation pushes the growing coleoptile to the soil surface and the radicle root and some lateral roots develop from the seed. This seminal root system absorbs water and nutrients until the V3 growth stage (3 leaves with collars).

Following emergence, the coleoptile and mesocotyl elongation stops, and the growth continues from the growing point (stem apex), which is located just above the mesocotyl and below the soil surface until the V5 - V6 growth stage (5 - 6 corn leaves with collars). The rapidly developing embryonic leaves grow through the coleoptilar tip.

Stages between VE and VT are designated numerically as V1, V2, …through V(n). The (n) represents stage with top leaf fully expanded before the VT stage. A leaf is considered fully expanded if the leaf collar (discolored line between the leaf blade and leaf sheath) is visible. The eventual number of leaves to be produced by a plant is determined by V6 - V7 growth stage.

Table 1. Vegetative growth stages of corn.
Vegetative stage Description

VE

Emergence (Fig. 2)

V1

First fully expanded leaf with the leaf collar (Fig. 3)

V2

Second fully expanded leaf with the leaf collar (Fig. 4)

V3

Third fully expanded leaf with the leaf collar

V(n)

nth fully expanded leaf with the leaf collar

VT

Tassel fully emerged (Fig. 5)

Description of corn plant during early development.

Fig. 1. Description of corn plant during early development. http://www.agronext.iastate.edu/corn/ 

Corn emergence.

Fig. 2. VE - Corn emergence.

First fully expanded leaf with the leaf collar.

Fig. 3. V1 - First fully expanded leaf with the leaf collar.

Second fully expanded leaf with the leaf collar.

Fig. 4. V2 - Second fully expanded leaf with the leaf collar.

Fig. 5. VT - Tassels fully emerged.

Fig. 5. VT - Tassels fully emerged. 

 

Reproductive (R) growth stages

The reproductive (R) stages are designated with R1 through R6 (Table 2). These stages start with silking (R1) and finish with physiological maturity (R6). Following R1, stage R2 refers to blister, R3 - milk, R4 - dough, R5 - dent, and R6 - physiological maturity (grain black layer).

At R1 , silks are first visible outside the husks. Pollination occurs when the falling pollen grains are caught by these silks. All silks emerge from the base to the tip in 2 to 5 days and remain receptive for up to two weeks. The silks will continue to elongate until fertilized. The ears pollinate from the base to the tip. Silks are pollinated within 2 - 3 days. For successful pollination it is important that silks emerge and pollinate at the same time. Moisture stress at this time causes poor pollination and reduced seed set, and therefore reduced yield. More information on conditions affecting corn can be found in chapter on “Environmental conditions affecting corn growth”.

At R2 stage, the kernels are white on the outside and have a blistered appearance. At R3, kernel is yellow outside and filled with a milk-colored fluid which is mainly starch. Kernels at this stage have 80% moisture. During the R4 stage, starch continues to accumulate and thickens to a pasty consistency. At R5 stage, most kernels are dented. The kernels at the R5 stage are drying down, beginning at the top, where a small hard white layer of starch is forming. The line indicating the hard starch layer will advance toward the base of the kernel.

The kernels reach their maximum dry matter weight at R6 stage when the hard starch layer has advanced completely to the cob and formed a brown or black abscission layer (‘black layer’) right above the kernel tip. The ‘black layer’ is an indication of physiological maturity. Kernels at the R6 stage have about 30 - 35% moisture content.

Table 2. Reproductive stages of corn. 
Reproductive stage Description

R1

Silking (Fig. 6)

R2

Blister

R3

Milk

R4

Dough

R5

Dent

R6

Physiological maturity (grain black layer) (Fig. 7)

corn: Silking stage.

Fig. 6. R1 - Silking stage.

corn: Physiological maturity (grain black layer).

Fig. 7. R6 - Physiological maturity (grain black layer).