Corn Growth Stages

In-season crop management is highly dependent on growth stage. Economic injury levels for pests are typically expressed in relation to corn growth stage; herbicide, fungicide, and insecticide labels often include use restrictions according to growth stage; and corn also takes up nutrients in different quantities during different growth stages. Understanding how corn growth stages are expressed will help you communicate clearly with your service providers; facilitate safe and effective application of crop protection products, and maximize crop nutrient use efficiency, especially for nitrogen.

The two phases of corn growth and development, vegetative, designated with "V," and reproductive, designated with "R." Corn plants progress through vegetative stages rapidly. In optimum growing conditions, a young corn plant can unfurl one new leaf from the whorl every 3 to 4 days. Once corn is about knee-high the leaves will unfurl as fast as one new leaf every 2-3 days. Plants typically develop approximately 20 leaves total.

The "collar" method

The most common way to determine vegetative corn growth stage is using the collar method. The collar is where the leaf sheath and leaf blade join. For this method, simply count the number of visible collars, including the first rounded leaf. In the example shown in Figure 1, counting from the bottom we see four leaf collars, shown with arrows; therefore, this corn is at the V4 growth stage.

Figure 1. Using the collar method, this plant is at the V4 growth stage. Photo: Heidi Reed.

However, as the plant starts to develop more leaves, leaves at the bottom may shrivel and fall off, making growth staging more difficult. For the most accurate staging of older plants, you can pull a plant by the roots, and carefully slice it in half from top to bottom. Distinguish the nodes and internodes--nodes look like horizontal bands across the inside of the stalk, and internodes are the whitish spaces between them. Next, identify the lowest obvious internode, typically about one-half inch in height; the node directly above it is typically the fifth node, which corresponds with the fifth leaf. Once you have identified the fifth node, you can just count the number of nodes above it to get your vegetative growth stage. Pioneer has an excellent video that demonstrates this method for staging corn plants, or you can read a more in-depth description of the process from Purdue University.

Vegetative Stages

VE – emergence, coleoptile breaks through the soil surface

V1 - one leaf collar is visible

V2 - second leaf collar is visible

V3 - third leaf collar is visible, plant begins to photosynthesize and rely on nodal root system

V4 - fourth leaf collar is visible

V5-V6 - fifth to sixth leaf collars are visible, growing point is above the soil surface, critical period of nitrogen uptake begins, and kernel row numbers are determined

V7-V(n) - seventh to nth leaf collars are visible, period of very rapid growth

VT – Tasselling – tassel is emerged, transitioning to reproductive phase

The "droopy leaf" method

Some product labels list restrictions as well as hail insurance adjustment calculations are based on the "Droopy Leaf" method, where all leaves with the tips of leaves facing downward are counted. As you can see in Figure 2, using the droopy leaf method, we would designate the same plant as V5. This is an expected discrepancy between the two methods, so make sure to use the appropriate method for your product. If it is unclear which method was used by the manufacturer to make the label, reach out to your chemical representative for clarification.

Figure 2. Using the droopy leaf method, this plant is at the V5 growth stage. Photo: Heidi Reed.

Of course, many products are applied beyond the vegetative growth stage. The reproductive growth stages are briefly described below.

Reproductive stages

R1 Silking – silks emerge from husks

R2 Blister – kernels are white on outside and inner fluid is clear

R3 Milk - kernels are yellow on the outside and inner fluid is milky-white

R4 Dough - milky inner fluid thickens from starch accumulation

R5 Dent – more than 50% of kernels are dented

R6 Physiological maturity – black layer formed

Keep in mind that every plant in the field will not be at exactly the same growth stage; you should make management decisions based on the growth stage of the majority of plants. If you need assistance determining the growth stage of your corn you can reach out to your local agronomy educator.