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I. BEFORE EMERGENCE
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A. Skip in rows where plants fail to emerge.
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Seed not sprouted.
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Seed not viable. Anhydrous or aqua ammonia injury.
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Excessive fertilizer (nitrogen and/or potash) placed too close to seed. Soil too dry, or water logged.
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B. Seed or sprout eaten or dug up.
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Seed swollen, but not sprouted.
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Mice, skunk, rats, crows, blackbirds.
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Rotted seed or seedlings.
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Seed hollowed out.
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Unemerged seedling dug up and/or entire plant eaten.
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II. EMERGENCE TO KNEE-HIGH
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A. Scattered problem spots of dead or poorly growing plants.
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Plants stunted, wilted and/or discolored.
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Cutworm damage.
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Plants cut off above or below ground.
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Sudden death of leaves or plants.
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Plants with rough gouged out feeding damage at or just below the soil surface.
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B. Wilting.
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Upper leaves roll and appear dull or sometimes purple; stunting of plants; plants may die.
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Dry surface soil, shallow planting (1/2 inch or less), sand blasting.
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Whorl dead.
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Crown roots not developing.
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Plants appear weak and sickly; wilting may occur; tunneling or girdling at or near soil surface is apparent.
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Lesser corn stalk borer caused by dry weather or planting into not fully decayed or green plant material.
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C. Plants discolored, stunted.
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Leaves appear sandblasted; leaves pale-green or whitish in color.
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Potassium deficiency. Excessive fertilizer or chemical uptake.
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Leaf edges yellow or dead.
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Yellowing or browning beginning from the tips.
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Excessive herbicide rates—(linuron (Lorox), ametryn (Evik), post emergence with oil, atrazine and other photosynthetic inhibitors: in severe cases, plants may die).
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Lower leaves dead, tips on upper leaves dying.
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Fertilizer injury.
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General yellowing of upper leaves.
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Sulfur deficiency.
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General yellowing of lower leaves.
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Excessive moisture. Nitrogen deficiency.
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Purpling or reddening of leaves from tips backwards; affects lower leaves initially; leaf tips may later turn dark brown and die.
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Phosphorus deficiency.
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Leaves slowly turn white to tan and die.
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Glyphosate (Roundup), other herbicide injury.
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Irregular light and dark mottling or mosaic on the leaves. Sometimes reddening of leaves.
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Maize dwarf mosaic or maize chlorotic dwarf viruses.
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Irregular light gray or silvery blotches on both sides of leaves on the east side of affected plants.
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Light streaking of leaves which develops into a broad band of bleached tissue on each side of the midribs; leaf-midribs and margins remain green; sometimes stalks and leaf edges appear to be tinted red or brown.
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Zinc deficiency.
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Bright yellow to white strips with smooth margins running the length of leaves; may appear on scattered plants throughout the field and sometimes only on one side of a plant.
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Genetic stripes.
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White or yellow stripes between leaf veins.
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Excessively acidic soil; Magnesium, iron, manganese, boron or sulfur deficiencies.
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Distinct bleached bands across leaf blades; leaf tissue may collapse at discolored bands, resulting in the leaf folding downward at this point.
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Air pollution injury; herbicides injury; cold banding.
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D. Plants discolored and stunted.
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Leaves yellow; plants spindly and stunted.
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Nitrogen deficiency. Sulfur deficiency-more pronounced on younger leaves than nitrogen deficiency; water logged soils, sting or stubby-root nematodes.
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Phosphorus deficiency-mild.
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E. Plants discolored and/or malformed.
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Whitish striping along leaf veins.
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Sulfur deficiency.
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Excessive tillering; stunting.
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Slight yellow-green tint; severely stunted; inability of leaves to emerge or unfold—leaf tips stick together, giving plants ladder-like appearance.
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Calcium deficiency; Herbicide injury—Amide herbicide (Dual, etc.).
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Leaves yellow and not fully expanded; roots sheared off or dried up.
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Over application of anhydrous or aqua ammonia.
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Leaves fail to unfurl properly, often leafing out underground; plants may be bent, lying flat on the soil surface.
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Excessive herbicide rates—Dicamba (Banvel) or metolachlor (Dual).
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Leaves stunted-twisted, and may appear knotted or hooked as with a walking cane.
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Thiocarbamate herbicide injury butylate (Sutan+); EPTC (Eradicane); or Metalachlor ( Dual).
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Shoots and roots malformed; general stunting of plants.
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Excessive rates of soil applied phenoxys ( 2,4-D) or dicamba
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Onion-leafing (leaves remain wrapped in a tall spike).
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High herbicide rates applied "over the top"; dicamba (Banvel), leaves may be narrower than normal; 2,4-D injury may cause temporary (7 to 10 days) stalk brittleness.
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Plants bent or twisted; stunted; irregular rows of holes in unfolded leaves.
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Stalk borer; Billbug.
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F. Lesions on leaves.
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Spots of dead tissue on leaves.
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Paraquat-Atrazine and oil herbicide injury; with paraquat, damage occurs only where the chemical contacts the plant tissue.
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Circular to oval cinnamon-brown pustules.
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Common and southern corn rusts. Southern corn leaf blight.
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G. Plant tissue removed.
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Whole plant cut off at ground level.
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Cutworm.
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Leaves entirely eaten off or large chunks of leaf tissue removed.
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Armyworms; Grasshoppers.
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Ragged holes in the leaves.
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Hail damage; European corn borers; Corn earworms; Cutworms—early larval damage.
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Shredding, tearing of leaves.
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Wind damage; Hail damage
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Rows of circular to elliptical holes across leaves.
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"Window effect" on leaves—leaves (area between upper and lower surface) eaten out, leaving a transparent 'mine' with bits of dark fecal material scattered throughout.
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Corn blotch leaf miners.
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Yellowed and weakened area on leaf midrib from tunneling feeding damage; often frass (sawdust-like excrement) evident around the feeding wound; the midrib will commonly break at this point, causing the leaf blade to fold down from the damage area.
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European corn borers.
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III. KNEE-HIGH TO TASSELING
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A. Severe wilting and/or death of plants.
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Sudden death of plants.
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Lightning (All plant material in an approximately circular area suddenly killed; plants along margin of affected area may be severely to slightly injured; severely injured plants may die later).
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Dieback of leaves wilting, then drying up of leaf tissue, beginning at leaf tips.
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Molybdenum deficiency (younger leaves may twist); Air pollution.
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Dead leaves or plants, usually at row ends.
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Excessive fertilizer or herbicide rates, or soil compaction.
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B. Plants discolored.
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Yellowing of plants, beginning with lower leaves.
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Potassium deficiency.
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Yellowing of leaf margins beginning at tips; affected tissue later turns brown and dies.
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Purpling or reddening of leaves from tip backward; affects lower leaves initially; leaf tips may turn dark brown and die.
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Phosphorus deficiency.
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Yellow to white interveinal striping on leaves.
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Genetic stripe (stripes have smooth margins; may appear on scattered plants throughout the field and, sometimes, only one side of a plant).
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Boron deficiency (initially white, irregularly shaped spots develop between veins which may coalesce to form white stripes that appear waxy and raised from leaf surface; plants may be stunted).
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Leaves completely white.
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Herbicides such as Zorial or Cotoran.
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Leaves turn whitish.
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Spider mites.
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Pale green to white stripes between leaf veins, usually on upper leaves
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Iron deficiency.
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Upper leaves show pale green to yellow interveinal discoloration; lower leaves appear olive green and somewhat streaked; severe damage appears as elongated white streaks. The center of which turns brown and falls out.
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Manganese deficiency.
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C. Plants discolored and malformed.
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Plants show stunting and/or a mottle or fine chlorotic strips in leaves. Leaves can be reddish.
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Maize dwarf mosaic virus or maize dwarf chlorotic virus.
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Stunting, tillering; twisting and rolling of leaves.
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Crazy top, plant virus.
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Plants darker green; stalks twisted at mid to upper half; ears often do not develop.
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Herbicide injury-butlylate (Sutan+) or EPTC (Eradicane).
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Twisting and bending at corn stalks above the ear shoot; ear may be malformed.
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Plants lodge or grow up in a curved "sled runner" or gooseneck shape.
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Soft, glistening white gall soon becomes black and dusty on stalks, leaves, ear or tassel.
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Common smut (fungus).
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D. Plant tissue removed.
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Ragged holes in the leaves and shredding of plants.
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Hail damage.
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Shredding, tearing of leaves.
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Wind damage.
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Leaf tissue skeletonized or lacy in appearance.
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Japanese beetles.
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Leaves entirely eaten off or large chunks of leaf tissue removed.
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Armyworms. Grasshoppers. Fall armyworms. Corn earworms. Livestock. Wildlife.
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Holes bored into stalks and area within stalk hollowed out by feeding damage.
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E. Lesions on plants.
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Oval, circular, or rectangular lesions, tan to brown in color.
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Southern corn leaf blight.
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Circular to oval, brick-red to cinnamon-brown pustules on leaves.
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Common and southern corn rust (fungi).
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IV. TASSELING TO MATURITY
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A. Silking impaired.
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Delayed silking or failure to silk.
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Cucumber beetles. Japanese beetles. Grasshoppers.
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Silks clipped off.
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B. Tassels malformed.
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Tassels fail to emerge.
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Boron deficiency (initially white, irregularly-shaped spots develop between veins which may coalesce and form white stripes that appear waxy and raised from leaf surface; plants may be stunted).
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Tassels and upper stalk and foliage bleached - premature drying.
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Anthracnose.
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Tassels develop as a mass of leaves.
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Crazy-top plant virus.
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Broken tassel from tunnelling.
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European corn borer.
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C. Plants discolored.
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Yellowing of leaf margins beginning at tips; affected tissue later turns brown and dies.
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Potassium deficiency.
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Reddish or purple leaf.
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Injury near leaf base, leaf injury; no ear on stalks and leaf is a carbohydrate sink.
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Irregular, purple-brown spots or blotches on sheaths.
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Purple sheath spots.
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D. Stalks malformed and/or broken.
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Lower stalk internodes and brace roots easily compressed; stalks may lodge.
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Fungal stalk rots.
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Plants lodge, stalk may break.
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European corn borer; wind; potassium deficiency-yellowing of leaf margins, beginning at tips; affected tissue later turns brown and dies.
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E. Premature death of all or some parts of plants.
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Sudden death of entire plant.
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Anthracnose leaf blight (fungus).
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Extensive areas of leaf tissue die prematurely, resulting in leaf drying.
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Top kill—premature death of all or portion of plants above ears.
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Severe drought.
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Early death of plant.
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F. Leaf tissue removed.
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Ragged holes in the leaves.
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Hail damage.
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Shredding, tearing of leaves.
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Wind damage.
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Small, irregular holes in leaves.
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European corn borer.
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Large, irregular holes in leaves.
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Grasshoppers; Fall armyworms.
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G. Plants discolored or stunted.
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Slight to severe stunting; yellowing and sometimes reddening of foliage.
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Maize dwarf mosaic or Maize chlorotic dwarf viruses.
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Reddish or purple stalk.
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Barren plant.
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H. Lesions on plants.
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Tan, oval to rectangular lesions, tan to brown in color.
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Southern corn leaf blight.
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Elongate, irregular brown water-soaked leaf stripes or spots on lower leaves.
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Bacterial leaf spot.
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White, dried areas between leaf veins.
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Air pollution.
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Numerous red/brown to black pustules on any above ground part, especially the leaves; leaves dry out.
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Common or southern rusts.
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I. Damage to ears.
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Large chunks removed from husks and ears; kernels eaten off.
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Corn earworm usually feed near the ear tip; European corn borer—bore into kernels and cobs; fall armyworms; cucumber beetles; corn sap beetles.
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Tunneling or chewing; feeding on kernels.
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Ears drop to ground.
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European corn borers (feeding damage to ear shanks and hybrid is susceptible to ear drop).
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Barren stalks.
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Maize dwarf mosaic or maize chlorotic dwarf viruses; High temperatures during pollination causing sterility; Drought; 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; 2, 4-D herbicide injury-applied during tasseling or pollen shed stage.
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Excessive ear shoots, which are leafy and barren.
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Crazy-top plant virus.
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Soft, glistening galls on the ear, later black and powdery.
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Common smut fungus.
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Ears twisted with irregular kernel rows and imperfectly developed ear tips.
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Phosphorus deficiency.
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Horizontal cut or split in seed coats.
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Silk-cut, most common in inbreds.
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Red streaking of seedcoats, most common at ear tips.
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Kernel red streak.
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J. Ears rot or are moldy.
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Individual kernels or scattered of kernels with pinkish mold.
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Fusarium fungal kernel ear rot.
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Pink to red mold growing through kernels from the silk end.
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Gibberella fungus or red ear rot.
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Powdery, green or blue-green mold on and between kernels, usually at ear tips.
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Penicillium fungal rot.
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Chaffy ears; soft cob.
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Nigrospora fungal ear or cob rot. Potassium deficiency.
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Husk bleached; white mold between kernels starting at the base of ear.
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Diplodia fungal ear rot.
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