Corn Growth Stages

Vegetative Stages (VE to VT)

Vegetative stages begin with emergence and continue through tasseling:

VE (Emergence): Coleoptile emerges from soil surface. Typically occurs 5-7 days after planting under good conditions. Early planting can delay emergence due to cold soils.

V1-Vn (Vegetative Leaves): Each new visible leaf collar represents a new V stage. Corn typically develops a new leaf every 3-5 days, depending on temperature. A hybrid that produces 18 leaves will have V1 through V18 stages.

VT (Tasseling): Last branch of tassel visible. Pollen shed begins 2-3 days later. This is the most critical period for yield determination — stress during VT and R1 can reduce kernel set.

Reproductive Stages (R1 to R6)

Reproductive stages begin with silking and end with physiological maturity:

R1 (Silking): Silks visible outside husks. Pollination begins. This is the most critical stage for yield — stress during R1 can reduce kernel set by 50% or more. Silks emerge from the ear shoot and catch falling pollen.

R2 (Blister): Kernels are white blisters with clear fluid. Occurs 10-14 days after R1. Kernel abortion can still occur under stress. Final kernel number is set by R2.

R3 (Milk): Kernels filled with milky white fluid. Occurs 18-22 days after R1. Kernel abortion is mostly complete. Stress reduces kernel weight, not number.

R4 (Dough): Kernel fluid is pasty/dough-like. Occurs 24-28 days after R1. Starch is rapidly accumulating. Kernel moisture around 70%.

R5 (Dent): Kernels begin to dent at the top. Occurs 35-42 days after R1. Most kernels have reached final size. Best time to estimate yield. Kernel moisture 55-60%.

R6 (Physiological Maturity): Black layer forms at base of kernel. All dry matter accumulation is complete. Kernel moisture 30-35%. Yield is set; only moisture loss remains.

When Yield Components Are Set

Understanding when each yield component is determined helps you identify yield-limiting factors:

• Ear size (rows around): Determined by V5-V12. Stress during this period reduces rows around the ear.
• Ear length (kernels per row): Determined by V12-V18. Stress reduces potential kernels per row.
• Kernel number: Final set at R1-R2 (pollination). Stress during pollination is most damaging.
• Kernel weight: Determined R2-R6. Stress reduces starch accumulation and final kernel weight.
• Final yield: Set at R6 (black layer). After this, only moisture changes.

Critical Stress Periods

Corn is most sensitive to stress at certain growth stages:

• V5-V12 (ear size determination): Stress reduces rows around ear
• V12-VT (ear length): Stress reduces potential kernels per row
• VT-R1 (pollination): Most critical period. Stress can reduce yield 50%+
• R1-R4 (grain fill): Stress reduces kernel weight
• R5-R6 (maturation): Stress has minimal yield impact, but can affect test weight

Heat stress (above 95°F) during pollination is particularly damaging because pollen viability decreases and silks can dry out before pollination occurs. Drought stress during pollination can cause similar damage.

Growing Degree Units (GDUs)

Corn development is driven by heat units, also called growing degree units (GDUs). Calculate daily GDU as: (max temp + min temp) ÷ 2 − 50, with max temp capped at 86°F and min temp not below 50°F.

Total GDUs needed for different hybrid maturities:

• Short season (80-90 CRM): 2,100-2,300 GDUs
• Mid season (95-105 CRM): 2,400-2,600 GDUs
• Full season (110-120 CRM): 2,700-2,900 GDUs

Typical GDU accumulation in US Corn Belt:

• May: 400-500 GDUs
• June: 600-700 GDUs
• July: 700-800 GDUs
• August: 650-750 GDUs
• September: 400-500 GDUs

Best Management Practices by Growth Stage

Different growth stages require different management focus:

Vegetative (VE-VT): Focus on weed control, nitrogen sidedress, and stand evaluation. Scout for insects and diseases.

VT-R1 (Pollination): Avoid stress. Don't apply fungicide or insecticide during active pollen shed. Irrigate if needed.

R1-R4 (Grain Fill): Protect leaf area with fungicide if disease pressure is high. Irrigate to maintain soil moisture.

R5 (Dent): Time to estimate yield. Plan harvest logistics. Watch for stalk lodging.

R6 (Black Layer): Harvest timing decision. Watch moisture and plan harvest schedule.