Corn
Zea mays
Wind-pollinated grain best planted in blocks rather than rows. Part of the classic Three Sisters planting with beans and squash.
Overview
Companion Planting
Pea
Green Bean
Runner Bean
Cucumber
Zucchini
Pumpkin
Sunflower
Sweet Pea
Tomato
CeleryToxicity
Corn (Zea mays) is listed as non-toxic to dogs, cats, and horses by the ASPCA. It is safe for human consumption and widely used in pet food. Note: corn cobs pose a choking and intestinal blockage hazard for dogs if swallowed, but this is a mechanical risk, not a toxicity issue.
Planting Tips
1 cm of water per m² equals 10 liters. Use the Watering Calculator for exact amounts.
Care Tip: Thin seedlings to 20-30 cm apart. Mound soil around the base of stalks when they reach 15 cm to support root stability. Remove suckers only if they compete with the main stalk. Mulch to retain moisture and suppress weeds.
Common Pests
Corn Earworm (Helicoverpa zea)
Symptoms: Larvae bore into the tips of ears through the silk channel, feeding on developing kernels. Frass (insect excrement) and damaged, partially eaten kernels are visible when husks are pulled back.
Treatment: Apply Bacillus thuringiensis (Bt) or spinosad directly to silks every 3-5 days during silking. For severe infestations, use pyrethrin-based insecticides. Remove and destroy infested ears.
Prevention: Apply a few drops of mineral oil or vegetable oil to the silk tips after they begin to brown. Plant early-maturing varieties to avoid peak moth activity. Use pheromone traps to monitor adult moth populations.
European Corn Borer (Ostrinia nubilalis)
Symptoms: Small holes in stalks and leaves with sawdust-like frass at entry points. Larvae tunnel into stalks, causing lodging (stalk breakage), broken tassels, and reduced ear development. Leaf feeding appears as shot-hole damage.
Treatment: Apply Bt (var. kurstaki) when larvae are small and before they bore into stalks. Trichogramma wasps are effective biological control agents released at egg-laying time. Destroy crop residues after harvest.
Prevention: Shred and plow under corn stalks after harvest to destroy overwintering larvae. Rotate crops. Plant Bt corn varieties where available. Scout for egg masses on leaf undersides in early summer.
Corn Rootworm (Diabrotica virgifera / D. barberi)
Symptoms: Larvae feed on roots, causing root pruning that leads to poor nutrient and water uptake, lodging ("goosenecking" where stalks lean and curve at the base), and stunted growth. Adults feed on silks, interfering with pollination.
Treatment: Apply soil-applied insecticides (granular chlorantraniliprole or clothianidin) at planting in fields with known infestations. Entomopathogenic nematodes can target larvae in the soil.
Prevention: Crop rotation is the most effective control — rotate corn with soybeans or another non-host crop. Avoid continuous corn planting. Monitor beetle populations with sticky traps in late summer to predict next year's larval pressure.
Common Diseases
Northern Corn Leaf Blight (Exserohilum turcicum)
Symptoms: Long, elliptical, grayish-green to tan lesions (5-15 cm) on leaves, starting on lower leaves and progressing upward. Severe infections cause extensive leaf death, reducing photosynthesis and grain fill.
Treatment: Apply foliar fungicides (azoxystrobin, propiconazole, or pyraclostrobin) at early tassel to silk stage if disease pressure is high. Remove and destroy heavily infected plant debris after harvest.
Prevention: Plant resistant hybrids (Ht genes). Practice crop rotation with non-host crops. Till under corn residue to reduce overwintering inoculum. Avoid overhead irrigation to reduce leaf wetness duration.
Common Rust (Puccinia sorghi)
Symptoms: Small, circular to elongate, reddish-brown to cinnamon-brown pustules on both leaf surfaces. Pustules rupture to release powdery spores. Severe infections cause premature leaf senescence and yield loss.
Treatment: Foliar fungicides (triazoles such as propiconazole, or strobilurins such as azoxystrobin) applied before or at early infection stages. Usually economically justified only in sweet corn or seed corn production.
Prevention: Plant rust-resistant varieties (Rp genes). Early planting helps avoid peak spore dispersal. Monitor fields regularly during warm, humid weather (optimal conditions: 16-23 degrees C with high humidity).
Gray Leaf Spot (Cercospora zeae-maydis)
Symptoms: Rectangular, gray to tan lesions that run parallel to leaf veins, giving a distinct blocky appearance. Lesions coalesce in severe cases, causing large areas of dead leaf tissue and significant yield reduction.
Treatment: Apply fungicides (strobilurins or triazole-strobilurin combinations) at VT (tasseling) to R1 (silking) if disease threshold is reached. Timing is critical — applications after significant leaf area is lost are ineffective.
Prevention: Plant tolerant hybrids. Rotate away from corn for at least one year. Tillage to bury infected residue reduces spore load. The disease is most severe in humid environments with prolonged leaf wetness and reduced-till continuous corn fields.