Corn Diagnostic Guide - Tasseling to Maturity



Possible Cause(s)

Silking impaired Delayed silking or failure to silk
  • Moisture stress
  • Stress on plants earlier in season
  • Plant population too high
  • Nutrient deficiency
  • Corn leaf aphids
  Silks clipped off
  • Corn rootworm beetles - northern, western and southern (see Corn Rootworm Damage)
  • Japanese beetles
  • Grasshopper Damage
Tassels malformed Tassels fail to emerge
  • Boron deficiency
  Tassels and upper stalk and foliage bleached, premature drying
  • Corn Anthracnose
  Tassels develop as a mass of leaves
  • Crazy top
  Leafy condition in the tassels
  • Sorghum downy mildew
Plants discolored Yellowing of leaf margins, beginning at tips; affected tissue later turns brown and dies
  • Potassium Deficiency
  Irregular, purple-brown spots or blotches on sheaths
  • Purple sheath spot
Stalks malformed and/or broken Lower stalk internodes easily compressed; stalks may lodge (break over) - (see Stalk Rot)
  • Diplodia stalk rot
  • Charcoal stalk rot
  • Gibberella stalk rot
  • Fusarium stalk rot
  Lower internodes easily compressed; black linear streaks on stalk surface
  • Anthracnose stalk rot
  Plants lodge, stalk may break
  • European Corn Borer
  • Southwestern corn borer
  • Potassium Deficiency
Premature death of all or some parts of plants Sudden death of entire plant
  • Stalk rot complex
  • Lightning
  • Frost
  Extensive areas of leaf tissue die prematurely resulting in leaf drying
  • Air pollution injury
  • Stewart's Disease
  • Northern corn leaf blight
  • Corn Anthracnose
  Top kill - premature death of all or portion of plants above ears.
  • Corn Anthracnose
Leaf tissue removed Ragged holes in the leaves
  • Hail damage
  Shredding, tearing of leaves
  • Hail/Wind damage
  Small, irregular holes in leaves
  • European Corn Borer - second brood larval feeding
  Large irregular holes in leaves
  • Grasshopper Damage
  • Fall armyworms
Plants discolored or stunted Slight to severe stunting; yellowing and sometimes reddening of foliage
  • Maize dwarf mosaic or Maize chlorotic dwarf
Lesions on plants Irregularly- or wavy-margined, pale green to yellow or pale brown streaks
  • Stewart's bacterial leaf blight
  Tan leaf lesions with parallel sides or spindle shaped and with buff to brown borders
  • Southern corn leaf blight
  Long, elliptical, gray-green or tan lesions
  • Northern corn leaf blight
  Small (1/16 to 3/8 inch) circular to oval lesions
  • Eyespot
  Elongated irregular brown water-soaked leaf stripes or spots on lower leaves
  • Bacterial leaf spots and stripe
  Oval, circular or rectangular lesions on leaves
  • Helminthosporium leaf spot
  Circular to oval lesions, brown centers with yellow to orange borders
  • Anthracnose leaf blight
  Numerous brown to black pustules on any above ground part, especially the leaves; leaves dry out
  • Common corn rust
Damage to ears Dark 'bruises' on husks
  • Hail damage - all plant material in an area affected; damage often more severe on one side of plant
  Large chunks removed from husks and ears; kernels eaten off
  • Grasshopper Damage
  • Birds - ears often upright, husks shredded
  • Rodents
  • Raccoons, squirrels or other animals
  Tunneling or chewing feeding damage on kernels
  • Corn Earworm - usually feeding near the ear tip
  • European corn borer - bore into kernels and cobs
  • Fall Armyworm
  • Corn rootworm beetles
  • Picnic beetles (secondary invaders)
  • Corn sap beetles - small brown or black beetles
  Ears break over and/or drop to ground
  • European corn borers - feeding damage to ear shanks
Ears or kernels malformed Ears not filled, partially filled, or smaller than normal ('nubbins')
  • Maize dwarf mosaic or Maize chlorotic dwarf
  • High temperatures during pollination causing sterility
  • Drought conditions
  • Timing of silking not synchronized with pollen shed
  • Plant population too high
  • Low fertility
  • Silks clipped back by insects
  • Corn leaf aphids - caused delay or failure of silking
  • Sorghum downy mildew
  • Herbicide injury
  Excessive ear shoots which are leafy and barren
  • Crazy top
  Soft, glistening galls on the ear, later black and powdery
  • Common smut
  Ears twisted with irregular kernel rows and imperfectly developed ear tips
  • Phosphorus deficiency
  Red streaking of seed coats; most common at ear tip
  • Kernel red streak
Ears rot or are moldy Individual kernels or scattered groups of kernels with pinkish mold
  • Fusarium Ear Rot
  Pink to red mold growing through kernels from the silk end
  • Gibberalla Ear Rot or red ear rot
  Powdery, green or blue-green mold on and between kernels, usually at ear tips
  • Penicillium rot
  Husks bleached; white mold between kernels
  • Diplodia Ear Rot

Planting to Emergence || Emergence to 8-10 Leaves || 8-10 Leaves to Tasseling || Tasseling to Maturity || Corn Diagnostic Guide

Adapted by James H. Hill, Iowa State University - Hancock County Extension Education Director, from information prepared by Dale M. Studt, retired ISU Extension Crop Production Specialist.

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