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Diagnosis of Corn Problems (Emergence to Knee-High (V-7) (Yellow-white…
Diagnosis of Corn Problems
Before Emergence
No Plant Emerged
Symptoms
No seed Planted
Planter problems: Clogged seed delivery system, Planter unit drive problems
Seed not sprouted
Ammonia injury, seed not viable, fertilizer in contact with seed, insect or disease, lack of oxygen (flooding)
Seed normal, not swelled
Soil too dry
Seed swelled, not sprouted
Soil dried out, soil too wet, seed not viable
Rotted seed or seedlings
Seed rots: pythium, diplodia, gibberella, fusarium, colletotrichum, etc.
Sprout twisted or leaves expanded underground
Mechanical injury, soil too deep, cloddy soil, Chloroacetsmide herbicide injury, insecticide injury, fertilizer burn, biuret damage
Seed eaten, dug up, or cut off
Symptoms
Seeds hollowed out
Insect damage: seed corn maggot, wireworm, seed corn beetle, thief ant, flea beetle larva
Plants pulled up, eaten
Bird damage: crows, pheasants, black birds. Rodent damage: mice voles, ground squirrels
Knee-To (V7) to Tasseling (Vt)
Plants have abnormal shape or position
Plants lean or fall over
Rootworm, Strong winds before brace roots have formed, nematodes, 2,4-D herbicide injury, mechanical injury
Stalks collapse from rot
European corn borer, 2,4-D herbicide injury, cutworm
Stalks collapse from stem not
Pythium stalk rot, bacterial stalk rot
Brace roots malformed or missing
Herbicide injury: 2, 4-D, dicamba, slugs
Plants malformed and discolored
Stunting, tillering, twisting
Crazy top (disease)
Galls; silvery white then black
Smut
Stunting, red leaves, excessive silvering
Maize dwarf mosaic and corn stunt, maize chlorotic mottle
Narrow leaves, striping
Sorghum downy mildew
Plants discolored, white, yellow, or purple on leaves
Leaves completely white, or top leaves or scattered, leaves white
Extreme heat
White stripes and some white leaves or scattered plants only
Genetic stripe
Yellowing of plants, beginning with lower leaves at leaf tip along midrib
Nitrogen deficiency, standing water
Yellowing of leaf margins, beginning at tips; affected tissue later turns brown dies
Potassium deficiency
Yellowing and necrosis of lower leaves beginning at leaf tip
Herbicide injury, photosynthetic inhibiting herbicide (applied post emergence)
Interveinal chlorosis or purpling
Amino acid synthesis inhibitor herbicide
Purpling or reddening of leaves,from tip backward; affects lower leaves initially; leaf tips may later turn dark brown and die
Phosphorous deficency
Yellow to white interveinal striping on leaves or reddening of leaves
Magnesium deficiency
Pale green to white striping on leaves
Iron deficiency
Upper leaves show pale green to yellow interveinal discoloration
Manganese deficieny
Lesions or necrotic spots on leaves
Paraquat, atrazine + oil, or other photosynthesis inhibitor, herbicides, foliar diseases: yellow leaf blight,anthracnose,stewart's leaf blight, helminthosporium leaf blights, (Southern, Northern, leaf spot)
Leaves have a window effect but neither surface is broken
Corn blotch leaf miner, leafhopper eggs
Upper leaves brown and sticky
Corn Leaf Aphid
Yellow or dead leaves, or plants
Ammonia burn (usually row ends only, in small acres) Glyphosphate herbicide injury
Holes in leaves
Leaves eaten
Insects: army-worm, variegated cutworm, stalk borer, European corn borer, southwestern corn borer, grasshopper, cutworm,livestock or wildlife
Leaves skeletonized or window-like
Western corn rootworm adult
Leaves shredded
Hail injury, wind damage
Emergence to Knee-High (V-7)
Scattered spots of dead or poorly growing plants
Symptoms
Uneven growth
Causes
Ammonia injury, Poor growing conditions, Uneven drainage.
Dead or stunted, discolored plants grading into normal plants at margin of affected area
Causes
Insect damage: garden symphylan, white grub, wireworm, stewarts leaf blight, ammonia injury cultivator injury, nematodes, glyphosphate drift injury
Plants discolored
Symptoms
Lower leaves dead, tips dying on upper leaves
Causes
Fertilizer injury, Chinch bug
Pale green color
Causes
Waterlogged soils, Glyphosate drift injury, Nitrogen deficiency, Potassium deficiency
Leaf edges yellow or dead
Causes
Potassium deficiency
Leaves purplish or reddish, especially at tips
Causes
Dinitroaniline herbacide injury, Glyphosate drift injury, Wind damage, Cold soils, Root insects: Grape colaspis, White grub, Garden symphylan, Wireworm, Neamatodes, Phosphorus deficiency
Plants Irregularly shaped, broken, or wilted
Symptoms
Plants twisted or broken off
Causes
Thiocarbamate herbicide injury, High acetamide herbicide rates, Cultivator damage, Insecticide injury
Leaves appear water-soaked,to grayish becoming necrotic
Causes
Ammonia injury, Frost, Paraquat
Leaves rolled, plants wilted
Causes
Drought stress, Root feding insects: Corn root aphid, Grape colaspis, White grub, Garden symphylan, Corn rootworm, Mechanical root injury to Nematodes
:
Leaves tightly rolled, not wilted
Causes
Herbicide injury, 2,4-D, dicamba, Chloroacetamide herbicide
Plants suddenly wilt and die, or cut off at ground level
Causes
Insect damage: Wireworm, Black cutworm, Cultivator injury
Small area of dead plants
Symptoms
Plant missing
Causes
Problem at or near planting
Symptoms
Dead plants present
Causes
Lightning, Cultivator injury
Plant tissue removed
Symptoms
Windowpane effect, Leaf skeletonizing
Causes
Insect damage: Southern corn rootworm adult, Cereal leaf beetle, Grape colaspis, Redheaded flea beetle, Palestriped flea beetle
Yellow-white areas in leaf
Symptoms
Plants mostly white
Causes
Genetic mutation, isoxaflutole, mesotrione, clomazone drift or carryover
Whitish striping along veins
Cuases
Sulfer deficency
:
Symptoms
Whitish or yellowish striping between leaf veins
Cuases
Nutrient deficiency: Iron, Manganese, Magnesium, Boron, Low pH
Symptoms
Only on occasional plants
Cuases
Physiological injury
Necrotic strips between veins
Causes
Stewart's blight leaf
Symptoms
Broad white areas, in center toward base of leaves, stunting, failer of internodes to elongate
Causes
Zinc deficiency
Narrow whitish scratches in leaf surface only
Causes
Corn leaf beetles
Leaves appear sandblasted or speckled, tips shredded
Causes
Thrips, Wind damage
Plants discolored and stunted
Symptoms
Dull grey areas on upper leaves, often where leaf bends
Causes
Frost or intense sunlight (scalding)
Leaves yellow; plants weak and stunted
Causes
Nitrogen, sulfer deficiency
purple or red discoloration of leaves, especially margins; stunting of roots
Causes
Imidazeolinon or sulfonylurea herbicide injury, Dinitroaniline injury, Dicamba herbicide injury, Phosphorus deficiency
Plant tissue removed
symptoms
Large holes in leaves
Causes
Variegated cutworm, sod webworm, common stalk borer, slugs
Leaf margins damaged
Causes
Yellow-striped armyworm, armyworm, fall armyworm
Rows of holes across leaves
Causes
Wireworm, cutworm, armyworm, billbug
Shredding or tearing of leaves
Causes
Wind, hail damage
:
Mature to Harvest
Stalks broken
Below the ear
Stalk rots: diplodia, pyhtium, gibberella, charcoal, anthracnose, weak stalks, potassium deficiency, southwestern corn borer
Stalks broken mainly above the ear
European corn borer, anthracnose top dieback
Ears on ground
Shank broken, whole ear dropped
Racoon, squirrel, european corn borer damage
Ears fallen from husks
Hybrid character, stalk rot
Rot or damage on ears or kernels
Whole ear or large section
Ear rots: Diplodia, Gibberella, Nigrospora, Physalospora, gray ear rot. deer, birds
Small areas on the ear of the individual kernels
Ear rots: fusarium, penicillium, aspergillus. Insect damage: fall armyworm, corn borer, corn earworm
Red stripes on kernels
Kernel red streak, hybrid character
Silking to Maturity
No silks apparent
Symptoms
Delayed silking or failure to silk
Population too high for hybrid, Drought stress, Low phosphorus supply, Nitrogen deficiency, Severe corn leaf aphid
Silks eaten off
Insect damage: Corn rootworm adult, Grasshopper, Japanese beetle, Woollybear caterpillar
No pollen; tassels sterile
Symptoms
Improper kernell set
2,4-D or dicamba applied at improper time, genetic male sterility
Leaves torn or pieces missing
Symptoms
Large or iregular areas eaten in leaves
Insect damage: grasshopper, fall armyworm
Damage to ear
Symptoms
Shucks eaten or open, kernels eaten or damaged
Grasshoppers, Birds, Rodents or other animals
Kernels tunneled and eaten
Insect damage: Corn earworm, Corn borer, Picnic beetle, Corn sap beetle, Fall armyworm
Ends of ears eaten off
Deer, Livestock
Discolored or dead plants
Symptoms
Reddish or purple leaves and stalk
Genetic character, Drought or other stress- see barren stalks, Injury to lea stalk, Corn stunt, Maize dwarf mosaic or other virus stress by corn leaf aphids Nematodes
Plant dies prematurely
Stalk rots, Severe corn borer damage or other stalk injury, drought
Dead frosted appearance of leaves
Foliar diseases: Helminthosporium leaf blights, stewart's leaf blight, Anthracnose, frost
Barren stalk, no ears, only stunted nubbins or scattered kernels
Population too high for hybrid or season, Low fertility, especially nitrogen drought , Corn leaf aphids, Ear smut, Maize dwarf mosaic; other viruses, Extreme heat prior to or during pollination, Nematodes
