Complete Farming Guide
Corn (Maize) Farming Guide
Zea mays
1.23 billion tonnes — the world's highest-producing cereal
Corn is the single most produced grain on Earth, surpassing both wheat and rice combined in total tonnage. It serves triple duty as human food, animal feed (60% of global production), and industrial feedstock for ethanol, starch, and sweeteners. From the Corn Belt of the US Midwest to the subsistence farms of sub-Saharan Africa, corn is cultivated on every continent except Antarctica. Its C4 photosynthesis pathway makes it exceptionally efficient at converting sunlight into biomass.
Quick Facts
Growing Season
Spring/Summer (Kharif)
Growth Period
90-130 days
Optimal Temp
18-32°C (64-90°F)
Water Needs
500-800mm
Top Producer
United States
Yield / Acre
1-5 tonnes (varies enormously by input level)
Corn (Maize) Growth Stages — What to Do at Every Stage
Emergence (VE-V3)
Days 0-15What to do
Plant when soil temperature at 2-inch depth is consistently above 10°C (50°F). Apply pre-emergence herbicide within 3 days of planting. Ensure seed-to-soil contact for uniform emergence. Target 32,000-36,000 plants/acre.
Watch for
Crusted soil preventing emergence. Seedling blight from cold, wet soils. Cutworms cutting seedlings at the soil line — check for missing plants in the row.
Early Vegetative (V4-V8)
Days 16-40What to do
Apply post-emergence herbicide if weed escapes are present. Side-dress nitrogen at V6 (when corn is knee-high) — this is the most efficient time for nitrogen uptake. Scout for early-season insects.
Watch for
Purple-red leaves indicate phosphorus deficiency in cold soils (usually resolves with warming). Whorl damage from fall armyworm larvae — tear open the whorl to check. Pale green/yellow leaves signal nitrogen hunger.
Late Vegetative (V9-VT)
Days 41-60What to do
This is the period of maximum nutrient and water demand. Ensure irrigation is keeping up — corn uses 0.25-0.35 inches of water PER DAY during this stage. All ear rows and potential kernel count are being determined NOW.
Watch for
Rolled leaves in the morning indicate severe drought stress. Gray leaf spot lesions appearing on lower leaves. Corn earworm moths laying eggs on silk — check the ear tip.
Tasseling & Silking (VT-R1)
Days 61-70What to do
This is THE most critical 2-week window in corn production. Each day of drought stress during silking reduces yield by 3-8%. Ensure continuous water supply. Do NOT apply foliar insecticides that kill pollinators during tasseling.
Watch for
Silk clipping by Japanese beetles or rootworm adults — clipped silks cannot be pollinated, resulting in missing kernels. Barren tips on ears from poor pollination. Extreme heat above 35°C causes pollen death.
Grain Fill & Maturity (R2-R6)
Days 71-130What to do
Maintain irrigation through the dough stage (R4). Crop water use gradually decreases. Scout for ear rots, especially in damaged ears. Plan harvest timing — corn is physiologically mature at black layer (R6, ~30% moisture).
Watch for
Stalk rot (push test: push the plant at ear height, if the stalk collapses, schedule early harvest). Ear rots (Fusarium: pink mold, Aspergillus: green-yellow). Ear drop from weak shanks. Harvest at 15-20% moisture for best quality.
Common Corn (Maize) Diseases — Identification Guide
Gray Leaf Spot
Cercospora zeae-maydis
What you will see
Rectangular, gray-tan lesions that run parallel to leaf veins, giving a distinctive "matchstick" shape. Lesions are sharply defined by the veins. Severe infection causes entire leaves to turn gray and die from the bottom up.
Conditions that favor it
Warm (22-30°C), humid conditions with heavy dew. Corn-on-corn rotation and no-till systems that leave infected residue on the soil surface. Worst in river bottoms and low-lying fields with poor air circulation.
Northern Corn Leaf Blight (NCLB)
Exserohilum turcicum
What you will see
Long (2-6 inches), cigar-shaped, gray-green lesions on leaves. Lesions start on lower leaves and move upward. Heavily infected leaves look like they have been singed with cigars. Can cause 30-50% yield loss if infection reaches the ear leaf before tasseling.
Conditions that favor it
Moderate temperatures (18-27°C), heavy dew and prolonged leaf wetness. Spreads from infected corn residue. Most severe in cool, humid growing seasons.
Fusarium Ear Rot
Fusarium verticillioides
What you will see
White or pinkish mold growing on individual kernels or groups of kernels, often starting at insect-damaged areas or the ear tip. Infected kernels are often lighter colored with a "starburst" pattern of white mycelium. Produces fumonisin mycotoxins.
Conditions that favor it
Warm, dry conditions during grain fill. Insect damage (especially earworm) creates entry points for the fungus. Drought-stressed corn is more susceptible. Fumonisins are a food safety concern at levels above 2-4 ppm.
Common Rust
Puccinia sorghi
What you will see
Small, circular to elongate, cinnamon-brown pustules on both leaf surfaces. Rub a finger across the pustule — brown, powdery spores come off. Heavy infection gives leaves a rough, sandpaper-like texture. Both leaf surfaces affected (unlike southern rust which prefers upper surface).
Conditions that favor it
Cool to moderate temperatures (16-23°C), high humidity. Spores blow in from southern regions on wind currents. Usually more of a cosmetic issue unless infection is early and severe.
Tar Spot
Phyllachora maydis
What you will see
Small, raised, black, tar-like spots on leaves that cannot be rubbed off (unlike rust pustules). Surrounding tissue may develop a tan "fish-eye" halo. Severe infections cause rapid and premature leaf death, reducing grain fill significantly.
Conditions that favor it
Cool nights (below 15°C), high humidity (>75%), prolonged leaf wetness. First confirmed in US Midwest in 2018, now rapidly expanding. Corn residue is the primary inoculum source.
Common Corn (Maize) Pests — Identification & Damage
Fall Armyworm
Damage
The single most destructive pest of corn in tropical and subtropical regions. Larvae feed in the whorl, destroying the growing point and leaving ragged, shot-hole damage on emerging leaves. Older larvae bore into ears through the husk, contaminating grain with frass. Yield losses of 20-50% are common in unmanaged fields across Africa and Asia.
How to identify
Larvae are green to brown with a distinctive inverted Y-shape on the head capsule and four dark spots arranged in a square on the last abdominal segment. Look for fresh, moist frass in the whorl. Larvae are most active at night. Threshold: 5% of plants with larvae in the whorl.
Corn Earworm (Helicoverpa zea)
Damage
Larvae feed on developing kernels at the ear tip, starting with the silks then boring into the ear. Creates entry points for ear rot fungi (Fusarium, Aspergillus). A single larva typically damages 2-3 square inches of kernels. In sweet corn, even minor damage makes ears unmarketable.
How to identify
Highly variable in color — green, brown, or pink with light and dark stripes. Feeds exclusively on the ear tip. Check for silk clipping and frass at the ear tip. Pheromone traps catch adult moths — high trap counts (50+/week) indicate significant egg-laying.
European Corn Borer
Damage
Larvae bore into stalks, ear shanks, and ear kernels. Stalk tunneling weakens the plant and causes stalk breakage and lodging. Ear shank tunneling causes ear drop before harvest. First-generation larvae feed on leaves and in the whorl; second-generation larvae bore directly into stalks and ears.
How to identify
Cream-colored larvae with small brown dots along the body, up to 25mm. Look for small round entry holes in the stalk with frass pushed out. Broken tassels and bent stalks are signs of internal feeding. Adult moths are tan with wavy dark bands on wings.
Western Corn Rootworm
Damage
Larvae feed on roots underground, removing root nodes and reducing the plant's ability to take up water and nutrients. Severe root pruning causes plants to "goose-neck" (lean over) and lodge. Root damage also creates entry points for soil-borne diseases. Adults feed on silks, interfering with pollination.
How to identify
Larvae are small white grubs (12mm) with a brown head, found by digging up root balls. Adults are yellow beetles with black stripes. Assess root damage on a 1-6 Iowa State scale — economic damage occurs at node injury score above 0.5. Most damaging in continuous corn rotations.
Stalk Borer
Damage
Larvae bore into corn stalks in the early vegetative stage, often entering at the whorl and tunneling downward. Damaged plants show wilting of the whorl leaves ("dead heart") or irregularly chewed leaves with rows of holes as the still-furled leaves were fed upon. Usually affects field edges near grassy waterways.
How to identify
Dark brown to purple larvae with a distinctive brown-white-brown banding pattern and a solid dark brown area behind the head. Found inside the stalk — split stalks lengthwise to find them. Damage is typically limited to the first 4-6 rows adjacent to grass borders.
Corn (Maize) Nutrient Management — NPK Guide
Nitrogen (N)
150-200 lb N/acre, with side-dress at V6 being most critical
Phosphorus (P)
40-60 lb P2O5/acre based on soil test
Potassium (K)
40-80 lb K2O/acre based on soil test
Application Timing
Apply 30-50 lb N at planting as starter, then side-dress 100-150 lb N at V6 (knee-high). Side-dress timing is critical — corn uptake rate peaks at V10-V14 when it absorbs 8-10 lb N/acre/day. P and K are typically broadcast pre-plant and incorporated.
Corn (Maize) Irrigation Schedule
Total Water Requirement
22-30 inches (560-760mm) total water use
Critical Stages
VT-R1 (tasseling through silking) is the absolute most critical stage. One day of severe water stress during silking reduces yield by 3-8%. The R2-R4 (blister through dough) stage is the second most sensitive. Corn uses 0.30-0.35 inches/day at peak demand.
Irrigation Frequency
Irrigate to maintain soil moisture above 50% of available water capacity. During peak demand, this may mean irrigating every 3-5 days in sandy soils or every 7-10 days in heavy soils.
Corn (Maize) Economics — Cost, Yield & Profit
Cost per Acre
$808-878/acre (US Corn Belt average)
Yield per Acre
180-220 bushels/acre (US irrigated); 40-80 bu/acre (African smallholder)
Revenue per Acre
$900-1,100/acre at $5-6/bushel (US)
Profit per Acre
$50-250/acre (highly variable)
Regional Context
Corn production costs in the US are the highest of any row crop, driven by seed ($100-120/acre), nitrogen ($80-120/acre), and machinery costs. Profit margins are thin and depend on achieving 200+ bu/acre yields. In Africa, smallholder corn costs $50-150/acre with yields of 1-2 t/acre. The global yield gap between best and worst producers is 5x, making corn the crop with the greatest potential for productivity improvement.
Frequently Asked Questions — Corn (Maize) Farming
When should I side-dress nitrogen on corn?
The optimal side-dress timing for corn is the V6 growth stage, when the plant is approximately knee-high (18-24 inches tall) with 6 visible leaf collars. At this stage, the corn root system has expanded enough to intercept the applied nitrogen, and the plant is entering its period of maximum nitrogen demand (V10-VT, when it can absorb 8-10 lb N/acre per day). Apply 100-150 lb N/acre as anhydrous ammonia, UAN solution, or urea. Delaying beyond V8 risks yield loss from nitrogen deficiency during the critical ear-size determination period. If using UAN solution, use drop nozzles to avoid leaf burn on larger corn. Some growers successfully split side-dress into two applications (V6 and V10) for better efficiency on sandy soils.
How do I scout for fall armyworm in corn?
Scout at least twice per week during the whorl stage (V4-V10). Check 20 plants at 5 locations across the field (100 plants total). Look for: (1) ragged, irregularly chewed leaves emerging from the whorl, (2) windows (translucent areas where larvae fed before leaves unfurled), (3) moist, sawdust-like frass in the whorl. To confirm, tear open the whorl and look for larvae — they have a distinctive inverted Y on their head. The treatment threshold is larvae in 5% of plants during the whorl stage. For ear-stage infestations, check 20 ears and look for frass and silk damage at the ear tip. Early morning and late afternoon scouting is most effective since larvae are more active during these cooler periods.
What causes barren (empty) ears on corn?
Barren ears result from pollination failure, and the most common causes are: (1) Drought stress during silking — silks emerge slowly or desiccate before pollen shed, preventing fertilization, (2) Heat stress above 35°C (95°F) during tasseling — pollen viability drops to near zero, (3) Uneven plant populations — small plants next to large ones get shaded and produce silks too late for available pollen, (4) Silk clipping by insects (rootworm adults, Japanese beetles) — when more than 50% of silks are clipped before pollination, (5) Planting too thick — populations above 38,000/acre in dryland conditions often cause barrenness. To prevent it, ensure adequate water during VT-R1, maintain optimal plant populations for your environment, and manage silk-clipping insects. Satellite monitoring through Cropple.AI can detect the early water stress that precedes pollination failure.
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