Corn Growth Stages and Management

Corn Growth Stages and Management

March 2025 | Written by: Jarrod Miller, Agronomy Extension Specialist

Growth Stages of Corn

Like most plants, corn growth progresses through three main phases: germination, vegetative, and reproductive stages. During germination, seeds break dormancy when soil temperatures exceed 50°F. They absorb (imbibe) water, triggering metabolic processes that lead to emergence and the start of the vegetative stage. (Figure 1)

Emergence is the first vegetative stage, labeled as VE when the corn plant may still have a cylindrical shape and lacks full leaf formation. This stage can be easy to miss, as the initial plant emerging from the ground is pale in color. While counting leaves can be challenging, the first true leaf that forms a collar around the stem and droops to the side is considered the first leaf (Figure 2). Vegetative stages are labeled based on leaf number: the first leaf with a collar is V1, the second leaf is V2, and so on (Figure 2). The final number of leaves may vary based on hybrid type or environmental factors but typically ranges between 12 and 16.

When counting leaves, consistency is key, as interpretations may vary. In Figure 3a, a corn plant at the V3 stage has a fourth leaf emerged, but it is not yet fully drooping or forming a complete collar around the stem. A light white mark is often visible where the leaf connects to the collar. Special care should be taken when stress has caused the early loss of lower leaves, as seen in Figure 4b. Marking leaf collars early in the season (as shown in Figure 3c) can be helpful for accurate leaf counting since lower leaves will eventually be scavenged for nutrients and senesce.

The last vegetative stage is the formation of the tassel (VT), which marks the transition to the reproductive stages and ear formation (Figure 4a). The first reproductive stage, R1, begins when silk emerges from the husk (Figure 4b), ready to be pollinated by the tassel.

As the corn ear matures, it progresses through several stages, starting with the blister stage (R2). At this stage, small bumps appear on the end of the white kernels, where the silk was attached (Figure 4c). The next stage is milk (R3), where the kernels turn yellow but still contain a milky fluid when cut open. In the dough stage (R4), the fluid inside the kernel begins to dry down, forming a dough-like consistency. As the kernel continues to dry, the milk line moves (Figure 5). The yellow color shifts downward from the tip of the kernel to the husk, becoming more noticeable at the tip.

This transition marks the beginning of the dent stage (R5), where an indentation appears on the surface of the kernel (Figures 4e/4f). The dent is considered complete when 50% of the kernels show this characteristic, signaling that the plant has reached R5. The final stage is physiological maturity (R6), also known as blacklayer, when yield is locked in. At this stage, you can observe black coloring at the bottom of the kernel by carefully separating it from the husk (Figure 4f).

Although corn is considered mature at this stage, the moisture content may still be around 30%. Additional drying will be necessary before harvest to reduce moisture-related price docks.

Growing Degree Days and Corn Stages

All plants grow best in warm weather, with growth slowing or ceasing at both low and high temperatures. To track this growth, growing degree days (GDD) were developed, offering a more accurate measure than simply counting days from planting. GDD is calculated by taking the maximum and minimum daily temperatures, adding them together, and dividing by two. Then, the base temperature is subtracted. If temperatures fall outside the plant's optimal growth range, the minimum or maximum temperature is used. For corn, this means a low of 50°F and a high of 86°F.

Based on this calculation, GDD for corn in Delaware are listed in Table 1. While averages provide a useful overview, it’s important to note that temperature response can vary depending on the hybrid and relative maturity.

Vegetative Growth Stages and Management

Growth stages can be used to make management decisions, including fertility, pest management, and irrigation needs. For early growth (VE-V3), check corn for emergence, stand counts, and pre-emergent weed control. Cold stress and compaction issues may also affect early growth. Nutrient deficiencies are not as prevalent at this stage, typically occurring after V4. Early insect pests to scout include slugs, cutworms, seed corn maggot, white grubs, and wireworms. Birds, particularly geese and deer, may also cause reduced stands. While soilborne diseases may reduce stands, management options are limited to seed treatments and hybrid selection for next season.

Between V4-V6,  sidedress applications are typically ideal. For soils with lower organic matter, V4 may be a better option for split-applying nitrogen. Tissue samples at this stage can indicate developing nutrient deficiencies but should be paired with soil tests for confirmation. Weed escapes should also be scouted at this stage, as well as any foliar diseases.

Past V6 and approaching VT, be sure to scout for gray leaf spot, Northern Corn Leaf Blight (NCLB), and Curvularia leaf spot, especially in fields with a history of disease. For insect management, scout for Japanese beetles and stink bugs, as stink bug injury is most damaging near VT when ear formation begins. Fertigation and foliar applications of nutrients can also be made based on tissue testing or visual symptoms. Irrigation management should also be a priority at this stage and through the rest of the season.
 

Reproductive Growth Stages and Management

Management options become limited as we reach the reproductive stages, with many yield-limiting factors already established. Scouting for kernel set throughout this cycle may reveal environmental stress, and irrigation should continue to be managed.

At the silking stage (R1), continue scouting for Japanese beetles, corn rootworm beetles, and stink bugs, as silk clipping can impact pollination. Northern Corn Leaf Blight (NCLB) should also be monitored, especially if weather conditions favor disease development, to determine if a fungicide application is necessary. Other foliar diseases, such as gray leaf spot, should also be considered.

As you approach the end of the reproductive cycle (R4-R6), scout fields for crown and stalk rots, which can indicate potential standability issues before harvest. Prioritizing harvest in affected fields can help reduce lodging losses.

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