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Diagnostic Guide for Corn Problems (Emergence to V7 (Scattered spots of…
Diagnostic Guide for Corn Problems
Before Emergence
Poor Emergence
Symptoms
No seed Planted
Causes
Planter Problems: Clogged seed delivery system.
Planter unit drive problems
Seed not sprouted
Causes
Ammoni injury
Seed not viable
Fertilizer in contact with seed.
Lack of oxygen (flooding)
Seed normal, not swelled
Causes
• Soil too Dry
Seed swelled, not sprouted
Causes
• Soil dried out.
• Soil too wet
• Seed not Viable
Rotted seed or seedlings
Causes
Seed Rots:
• Pythium
• Diplodia
• Gibberella
• Fusarium
• Colletotrichum
Sprout twisted or leaves expanded underground
Causes
• Mechanical injury
• Seed to deep
• Cloddy Soil
• Chloroacetamide herbicide injury
• Insecticide Injury
• Fertilizer burn
• Biuret damage
Seeds hollowed out
Causes
Insect Damage:
• Seed corn maggot
• Wireworm
• Seed corn beetle
• Thief ant
• Flea beetle Larva
Plants Pulled up, eaten
Causes
Bird damage:
• Crows
• Pheasants
• Blackbirds
Rodant Damage
• Mice
• Voles
• Ground Squirrels
Emergence to V7
Scattered spots of dead or poorly growing plants
Symptoms
Uneven gowth
Causes
• Ammonia injury
• Poor growing conditions
• Uneven drainage
Dead or stunted, discolored plants grading into normal plants at margin of affected area
Insect Damage:
• Garden symphylan
• White grubs
• Wireworm
• Stewart's leaf blight
• Ammonia injury
• Cultivator injury
• Nematodes
• Glyphosate drift injury
Plants discolored
Symptoms
Lower leaves dead, tips dying on upper leaves
Casues
• Fertilizer injury
• Chinch bug
Pale green color
• Waterlogged soils
• Glyphosate drift injury
• Nitrogen deficiency
Leaf edges yellow or dead
Potassium deficiency
Leaves purplish or reddish, especially at tips
• Dinitroaniline herbicide injury
• Glyphosate drift injury
• Wind damage
• Cold soils
• Nematodes
• Phosphorus deficiency
Root Insects :
• Grape colaspis
• White grub
• Garden symphylan
• Wireworm
Plants irregularly shaped, broken, or wilted
Symptoms
Plants twisted or broken off
•Thiocarbamate herbicide injury
• High acetamide herbicide rates
• Cultivator damage
• Insecticide
Leaves appear water-soaked, to grayish becoming necrotic
• Ammonia injury
• Frost
• Paraquat injury
Leaves rolled, plants wilted
• Drought stress
• Root feeding insect;
• Corn root aphid
• Grape colaspis
• White grub
• Garden symphylan
•Cron rootworm
Leaves tightly rolled, not wilted
Herbicide injury;
•2,4-D, dicamba
• Choroacetamide herbicide
Plants suddenly wilt and die, or cut off at ground level
Insect Damage;
• Wireworm
• Black cutworm
• Cultivator injury
Small area of dead plants
Symptoms
Plants missing
Problem at or near planting
Dead plants present
•Lightning
• Cultivator injury
Plants discolored and stunted
Symptoms
Dull grey areas on upper leaves, often where leaf bends
Frost or intense sunlight (scalding)
Leaves yellow; plants weak and stunned
Nitrogen, sulfur deficiency
Purple or red discoloration of leaves, especially margins; stunting of roots
• Imidazolinone or sulfonylurea herbicide injury
• Diniroaniline herbicide injury
• Dicamba herbicide injury
• Phosphorous deficiency
Yellow-white areas in leaf
Symptoms
Plant Mostly white
• Genetic mutation
• Isoxaflutole, mesotrione, clomazone drift or carryover
Whitish or yellowish striping between leaf veins
Nutrient deficiency;
• Iron
• Manganese
• Magnesium
• Boron
•Low pH
Only on occasional plants
Physiological injury
Necrotic strips between veins
Stewarts leaf blight
Whitish Striping along veins
Sulfur deficiency
Broad white areas, in center toward base of leaves, stunting, failure of internodes to elongate
Zinc deficiency
Narrow whitish scratches in leaf surface only
Corn Flea beetles
Leaves appear sandblasted or speckled, tips shredded
• Thrips
• Wind Damage
Plant tissue removed
Symptoms
Window effect, leaf skeletonizing
Insect damage;
• Southern corn rootworm adult
• Cereal leaf beetle
• Grape colaspis
• Readheaded flea beetle
• Palestriped flea beetle
Plants tissue removed
Symptoms
Large holes in leaves
• Variegated cutworm
• Sod webworm
• Common stalk borer
• Slugs
Leaf Margins damaged
• Yellow-striped armywrom
• Armyworm
• Fall Armyworm
Rows of holes across leaves
• Wireworm
• Cutworm
• Armyworm
• Billbug
Shredding or tearing of leaves
Wind, hail damage
V7-VT
Plants have abnormal shape or position
Symptoms
Plant lean or fall over
• Rootwrom
• 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 rot
• Pythium stalk rot
• Bacterial stalk rot
Brace roots malformed or missing
• Herbicide injury
• 2,4-D, Dicamba
• Slugs
Plants malformed and discolerd
Symptoms
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
Symptoms
Leaves completely white, or top leaves or scattered leaves white
Extreme heat
White stripes and some white leaves on 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 and 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
Phosphorus deficiency
Yellow to white interveinal striping on leaves or redding of leaves
Magnesium deficiency
Pale green to white striping on leaves
Iron deficiency
Upper leaves show pale green to yellow interveinal discoloration
Manganese deficiency
Lesions or necrotic spots on leaves
• Paraquat, atrazine + oil, or other photosynthetic inhibitor herbicides
• Foliar diseases:
Yellow leaf blight
Antheracnose
Stewart's leaf blight
Helminthosporium leaf blight
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
• Glyphosate herbicide injury
Holes in leaves
Symptoms
Leaves eaten
• Insects
Armyworm
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
R1-R6
No Silks apparent
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
-Woolybear caterpillar
No pollen; tassels sterile
Improper kernel set
• 2,4-D or dicamba applied at improper time
• Genetic male sterility
Leaves torn or pieces missing
Large, irregular areas eaten in leaves
• Insect Damage
-Grasshopper
-Fall armyworm
Damage to ear
Shucks eaten or open, Kernels eaten or damaged
• Grasshopper
• Birds
• Rodents or other animals
• Insect damage
-Corn earworm
-Corn borer
-Picnic beetle
-Corn sap beetle
Fall aryworm
Ends of ears eaten off
Deer, Livestock
Discolored or dead plants
Reddish or purple leaves and stalk
• Genetic character
• Drought or other stress-see barren stalks
• Injury to leaf or 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
