Corn:Key

KEY TO CORN PESTS AND NUTRITIONAL DISORDERS

Seed

Seed disorders are limited to disorders while in the ground and not to potential disorders inherent in the seed.

BROWN

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

Seedling

GRAY

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

PINK

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

TAN

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

WHITE

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

YELLOW

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

Root-Crown

PINK

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

TAN

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

WHITE

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

BROWN

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

GRAY

Seed Decay and Seedling Blight

Decayed seedlings are soft, and covered with fuzzy fungal growth; post-emergence damping-off appears as yellowing and wilting; depending on the fungi, roots may be grayish white, tan, pink, brown and firm or shriveled; poor or no stand in the field

BROWN

Root Rots

Stunting, uneven growth, chlorosis, small or poorly filled ears, wilting; small yellow-brown lesions develop on the roots, which later turn dark brown and obviously decayed; fine decayed roots slough off after rotting

YELLOW

Root Rots

Stunting, uneven growth, chlorosis, small or poorly filled ears, wilting; small yellow-brown lesions develop on the roots, which later turn dark brown and obviously decayed; fine decayed roots slough off after rotting

No Distinct Discoloration

Nematodes

Poor or uneven stands in the field; chlorosis, stunting, and small or poorly filled ears occur in patches in the field; symptoms on roots can include stunting, malformation, and discolored lesions

Stem

BLACK

Anthracnose Stalk Rot

Blackening of the stalk rind by narrow, water-soaked lesions turning very dark and shiny; lesions coalesce to form large black blotches or streaks; top dieback may occur 4-6 weeks after pollination and upper leaves turn yellow or red and dry up

Bacterial Stalk Rot

Upper leaves become gray to brown with shortened internodes; outside of the stalk may be brown to black and water-soaked; leaf tissue within the whorl and the growing point of the stem within the whorl are brown, wet, slimy and have a foul odor

Charcoal Rot

Pith and stalk rind appear gray due to the number of tiny black sclerotia that develop; the pith tissue is disintegrated, leaving the vascular tissue with a granular, gray appearance

Diplodia Stalk Rot

Numerous small, black pycnidia develop in the lower internodes of the stalk; under wet conditions, a white mold may develop on the stalk surface

BROWN

Bacterial Stalk Rot

Upper leaves become gray to brown with shortened internodes; outside of the stalk may be brown to black and water-soaked; leaf tissue within the whorl and the growing point of the stem within the whorl are brown, wet, slimy and have a foul odor

Common Smut

Galls can form on stalks, leaves, ear, and tassels as swollen, distorted growths with a glistening white membrane that ruptures to reveal a mass of dark brown or black powdery spores; galls cause yield loss, lodging, and kernel loss

Fusarium Stalk Rot

Brown streaks on the lower internodes; the rotted pith tissue may be a whitish pink to salmon color; general stalk rot symptoms

Pythium Stalk Rot

Decay of the first internode above the soil; the rind and pith become soft, brown, and water-soaked; decayed tissue often carries a strong odor; stalk usually twists and falls over but the plant may remain green for weeks

Stalk Rots: Anthracnose Stalk Rot; Diplodia Stalk Rot; Fusarium Stalk Rot; Gibberella Stalk Rot

Disintegration of the pith tissue; pith usually becoming brown at the nodes and may have a water-soaked appearance; plants may die before reaching maturity; leaves wilt and die turning brown, gray, or purple; streaks on the stalks; lodging

DARK

Anthracnose Stalk Rot

Blackening of the stalk rind by narrow, water-soaked lesions turning very dark and shiny; lesions coalesce to form large black blotches or streaks; top dieback may occur 4-6 weeks after pollination and upper leaves turn yellow or red and dry up

Gibberella Stalk Rot

Dark streaks on the lower internodes; distinct pink or red discoloration of the pith tissue

GRAY

Bacterial Stalk Rot

Upper leaves become gray to brown with shortened internodes; outside of the stalk may be brown to black and water-soaked; leaf tissue within the whorl and the growing point of the stem within the whorl are brown, wet, slimy and have a foul odor

Charcoal Rot

Pith and stalk rind appear gray due to the number of tiny black sclerotia that develop; the pith tissue is disintegrated, leaving the vascular tissue with a granular, gray appearance

Stalk Rots: Anthracnose Stalk Rot; Diplodia Stalk Rot; Fusarium Stalk Rot; Gibberella Stalk Rot

Disintegration of the pith tissue; pith usually becoming brown at the nodes and may have a water-soaked appearance; plants may die before reaching maturity; leaves wilt and die turning brown, gray, or purple; streaks on the stalks; lodging

GREEN

Pythium Stalk Rot

Decay of the first internode above the soil; the rind and pith become soft, brown, and water-soaked; decayed tissue often carries a strong odor; stalk usually twists and falls over but the plant may remain green for weeks

PINK

Fusarium Stalk Rot

Brown streaks on the lower internodes; the rotted pith tissue may be a whitish pink to salmon color; general stalk rot symptoms

Gibberella Stalk Rot

Dark streaks on the lower internodes; distinct pink or red discoloration of the pith tissue

PURPLE

Stalk Rots: Anthracnose Stalk Rot; Diplodia Stalk Rot; Fusarium Stalk Rot; Gibberella Stalk Rot

Disintegration of the pith tissue; pith usually becoming brown at the nodes and may have a water-soaked appearance; plants may die before reaching maturity; leaves wilt and die turning brown, gray, or purple; streaks on the stalks; lodging

RED

Anthracnose Stalk Rot

Blackening of the stalk rind by narrow, water-soaked lesions turning very dark and shiny; lesions coalesce to form large black blotches or streaks; top dieback may occur 4-6 weeks after pollination and upper leaves turn yellow or red and dry up

Gibberella Stalk Rot

Dark streaks on the lower internodes; distinct pink or red discoloration of the pith tissue

WHITE

Common Smut

Galls can form on stalks, leaves, ear, and tassels as swollen, distorted growths with a glistening white membrane that ruptures to reveal a mass of dark brown or black powdery spores; galls cause yield loss, lodging, and kernel loss

Diplodia Stalk Rot

Numerous small, black pycnidia develop in the lower internodes of the stalk; under wet conditions, a white mold may develop on the stalk surface

Fusarium Stalk Rot

Brown streaks on the lower internodes; the rotted pith tissue may be a whitish pink to salmon color; general stalk rot symptoms

YELLOW

Anthracnose Stalk Rot

Blackening of the stalk rind by narrow, water-soaked lesions turning very dark and shiny; lesions coalesce to form large black blotches or streaks; top dieback may occur 4-6 weeks after pollination and upper leaves turn yellow or red and dry up

Maize Dwarf Mosaic

Stippled mottle or mosaic of light and dark green that may develop into narrow streaks on the youngest leaves; shortening of internodes; stunted, bunchy appearance of the plant; as plants ages, mosaic symptoms disappear and young leaves appear yellow

Leaf

BLACK

Anthracnose Leaf Blight

Lower leaves show symptoms first; leaf lesions are oval tan or brown with a dark brown or purple margin; black acervuli, spiny structures develop on dead leaf tissue; lesions may coalesce into large dead areas; leaves may turn yellow and wither

Common Rust

Early symptoms are chlorotic flecks on the leaf surface which develop into small, powdery, brick-red pustules; leaf tissue around the pustules may become yellowed, or it may die; lesions sometimes form a band across the leaf; death may occur

Goss' Bacterial Wilt

Leaf lesions are long, gray-green to black, water-soaked, with wavy edges; streaks resembling freckles within the lesions; droplets of bacterial exudate ooze from these freckles leaving crystalline deposits on the leaf surface; lesions fade to a tan color

Helminthosporium Leaf Spot

Symptoms vary from tan, oval to circular lesions on leaves with a black felty mold on the kernels and brown spots on the leaves to long, narrow tan lesions with a darker border on leaves, sheaths, and husks; severe infection can cause death of the leaves

Southern Rust

Pustules on the upper leaf surface are small and densely scattered over the leaf; pustules are orange and erupt into telia and become brown to black, often forming dark circles around the original pustule

BROWN

Anthracnose Leaf Blight

Lower leaves show symptoms first; leaf lesions are oval tan or brown with a dark brown or purple margin; black acervuli, spiny structures develop on dead leaf tissue; lesions may coalesce into large dead areas; leaves may turn yellow and wither

Common Smut

Galls can form on stalks, leaves, ear, and tassels as swollen, distorted growths with a glistening white membrane that ruptures to reveal a mass of dark brown or black powdery spores; galls cause yield loss, lodging, and kernel loss

Eyespot

Small, water-soaked or chlorotic circular spots appear on older leaves; tissue at the center of the spot later dies and turns tan with a brown or purple ring at the margin; the spot is surrounded by a yellow halo and can coalesce into necrotic areas

Helminthosporium Leaf Spot

Symptoms vary from tan, oval to circular lesions on leaves with a black felty mold on the kernels and brown spots on the leaves to long, narrow tan lesions with a darker border on leaves, sheaths, and husks; severe infection can cause death of the leaves

Holcus Leaf Spot

Similar to other corn leaf blights; lesions are oval to rectangular, dark green and water-soaked becoming dried out and turning light brown sometimes with a reddish brown margin with a papery texture

Southern Leaf Blight

Leaves, husks, stalks, leaf sheaths, shanks, ears and cobs are affected; lesions may be tan and purple and rectangular in shape with reddish brown margins or rectangular to elliptical with a reddish brown border that may be surrounded by a chlorotic zone

Southern Rust

Pustules on the upper leaf surface are small and densely scattered over the leaf; pustules are orange and erupt into telia and become brown to black, often forming dark circles around the original pustule

Stewart's Disease

Lesions begins as pale green to yellow streaks turning brown as the tissue dies; margins of the streaks are usually wavy but generally following leaf veins; entire leaves can be blighted; bleached, dead tassels and decayed cavities in the stalk may result

GRAY

Goss' Bacterial Wilt

Leaf lesions are long, gray-green to black, water-soaked, with wavy edges; streaks resembling freckles within the lesions; droplets of bacterial exudate ooze from these freckles leaving crystalline deposits on the leaf surface; lesions fade to a tan color

Gray Leaf Spot

Symptoms first appear on lower leaves around the time of tasseling; leaf lesions are up to 2 inches long, narrow, rectangular, and light tan, later turning gray; lesions can coalesce and kill entire leaves

Northern Leaf Blight

Leaf lesions are 1-6 inches long and elliptical and gray-green turning pale gray or tan; under moist conditions, the lesions produce dark gray spores, sometimes in rings on the lower leaf surface; severely blighted plants have entire leaves dead

GREEN

Goss' Bacterial Wilt

Leaf lesions are long, gray-green to black, water-soaked, with wavy edges; streaks resembling freckles within the lesions; droplets of bacterial exudate ooze from these freckles leaving crystalline deposits on the leaf surface; lesions fade to a tan color

Holcus Leaf Spot

Similar to other corn leaf blights; lesions are oval to rectangular, dark green and water-soaked becoming dried out and turning light brown sometimes with a reddish brown margin with a papery texture

Maize Dwarf Mosaic

Stippled mottle or mosaic of light and dark green that may develop into narrow streaks on the youngest leaves; shortening of internodes; stunted, bunchy appearance of the plant; as plants ages, mosaic symptoms disappear and young leaves appear yellow

Northern Leaf Blight

Leaf lesions are 1-6 inches long and elliptical and gray-green turning pale gray or tan; under moist conditions, the lesions produce dark gray spores, sometimes in rings on the lower leaf surface; severely blighted plants have entire leaves dead

Stewart's Disease

Lesions begins as pale green to yellow streaks turning brown as the tissue dies; margins of the streaks are usually wavy but generally following leaf veins; entire leaves can be blighted; bleached, dead tassels and decayed cavities in the stalk may result

ORANGE

Southern Rust

Pustules on the upper leaf surface are small and densely scattered over the leaf; pustules are orange and erupt into telia and become brown to black, often forming dark circles around the original pustule

PURPLE

Anthracnose Leaf Blight

Lower leaves show symptoms first; leaf lesions are oval tan or brown with a dark brown or purple margin; black acervuli, spiny structures develop on dead leaf tissue; lesions may coalesce into large dead areas; leaves may turn yellow and wither

Eyespot

Small, water-soaked or chlorotic circular spots appear on older leaves; tissue at the center of the spot later dies and turns tan with a brown or purple ring at the margin; the spot is surrounded by a yellow halo and can coalesce into necrotic areas

Southern Leaf Blight

Leaves, husks, stalks, leaf sheaths, shanks, ears and cobs are affected; lesions may be tan and purple and rectangular in shape with reddish brown margins or rectangular to elliptical with a reddish brown border that may be surrounded by a chlorotic zone

RED

Common Rust

Early symptoms are chlorotic flecks on the leaf surface which develop into small, powdery, brick-red pustules; leaf tissue around the pustules may become yellowed, or it may die; lesions sometimes form a band across the leaf; death may occur

Southern Leaf Blight

Leaves, husks, stalks, leaf sheaths, shanks, ears and cobs are affected; lesions may be tan and purple and rectangular in shape with reddish brown margins or rectangular to elliptical with a reddish brown border that may be surrounded by a chlorotic zone

TAN

Anthracnose Leaf Blight

Lower leaves show symptoms first; leaf lesions are oval tan or brown with a dark brown or purple margin; black acervuli, spiny structures develop on dead leaf tissue; lesions may coalesce into large dead areas; leaves may turn yellow and wither

Eyespot

Small, water-soaked or chlorotic circular spots appear on older leaves; tissue at the center of the spot later dies and turns tan with a brown or purple ring at the margin; the spot is surrounded by a yellow halo and can coalesce into necrotic areas

Goss' Bacterial Wilt

Leaf lesions are long, gray-green to black, water-soaked, with wavy edges; streaks resembling freckles within the lesions; droplets of bacterial exudate ooze from these freckles leaving crystalline deposits on the leaf surface; lesions fade to a tan color

Gray Leaf Spot

Symptoms first appear on lower leaves around the time of tasseling; leaf lesions are up to 2 inches long, narrow, rectangular, and light tan, later turning gray; lesions can coalesce and kill entire leaves

Helminthosporium Leaf Spot

Symptoms vary from tan, oval to circular lesions on leaves with a black felty mold on the kernels and brown spots on the leaves to long, narrow tan lesions with a darker border on leaves, sheaths, and husks; severe infection can cause death of the leaves

Northern Leaf Blight

Leaf lesions are 1-6 inches long and elliptical and gray-green turning pale gray or tan; under moist conditions, the lesions produce dark gray spores, sometimes in rings on the lower leaf surface; severely blighted plants have entire leaves dead

Southern Leaf Blight

Leaves, husks, stalks, leaf sheaths, shanks, ears and cobs are affected; lesions may be tan and purple and rectangular in shape with reddish brown margins or rectangular to elliptical with a reddish brown border that may be surrounded by a chlorotic zone

WHITE

Common Smut

Galls can form on stalks, leaves, ear, and tassels as swollen, distorted growths with a glistening white membrane that ruptures to reveal a mass of dark brown or black powdery spores; galls cause yield loss, lodging, and kernel loss

YELLOW

Anthracnose Leaf Blight

Lower leaves show symptoms first; leaf lesions are oval tan or brown with a dark brown or purple margin; black acervuli, spiny structures develop on dead leaf tissue; lesions may coalesce into large dead areas; leaves may turn yellow and wither

Common Rust

Early symptoms are chlorotic flecks on the leaf surface which develop into small, powdery, brick-red pustules; leaf tissue around the pustules may become yellowed, or it may die; lesions sometimes form a band across the leaf; death may occur

Eyespot

Small, water-soaked or chlorotic circular spots appear on older leaves; tissue at the center of the spot later dies and turns tan with a brown or purple ring at the margin; the spot is surrounded by a yellow halo and can coalesce into necrotic areas

Stewart's Disease

Lesions begins as pale green to yellow streaks turning brown as the tissue dies; margins of the streaks are usually wavy but generally following leaf veins; entire leaves can be blighted; bleached, dead tassels and decayed cavities in the stalk may result

No Distinct Discoloration

Crazy Top

Tassel bracts may proliferate causing a very bushy appearance of the plant; internodes may be short or long, there may be a proliferation of ear shoots, leaves that are narrow and straplike, excessive tillering, or lack of ear and tassel formation

Fruit

BLACK

Diplodia Ear Rot

White mold on the ear turning to a grayish brown color rotting the entire ear, including kernels; mold may be apparent on the outside of the husk or on the shank; raised black bumps can usually be seen on the moldy husk or kernels

Head Smut

Galls form on the tassels and ears and are covered with a thin layer of tissue that breaks open to expose the black spore masses and threadlike remains of the vascular bundles; leaf-like growth develops on the tassel and ears; plants may be dwarfed

BROWN

Aspergillus Ear and Kernel Rot

Gray-green, powdery mold develops on kernels; kernels are brownish, lightweight, and shrunken; the rot may begin at the tip of the ear or follow along tracks made by insect injury

Common Smut

Galls can form on stalks, leaves, ear, and tassels as swollen, distorted growths with a glistening white membrane that ruptures to reveal a mass of dark brown or black powdery spores; galls cause yield loss, lodging, and kernel loss

Diplodia Ear Rot

White mold on the ear turning to a grayish brown color rotting the entire ear, including kernels; mold may be apparent on the outside of the husk or on the shank; raised black bumps can usually be seen on the moldy husk or kernels

Fusarium Ear and Kernel Rot

White to pink or salmon-colored cottony mold beginning on the ear; affected kernels may be scattered or clustered throughout the ear and are often tan or brown colored or have white streaks

GRAY

Aspergillus Ear and Kernel Rot

Gray-green, powdery mold develops on kernels; kernels are brownish, lightweight, and shrunken; the rot may begin at the tip of the ear or follow along tracks made by insect injury

Diplodia Ear Rot

White mold on the ear turning to a grayish brown color rotting the entire ear, including kernels; mold may be apparent on the outside of the husk or on the shank; raised black bumps can usually be seen on the moldy husk or kernels

GREEN

Aspergillus Ear and Kernel Rot

Gray-green, powdery mold develops on kernels; kernels are brownish, lightweight, and shrunken; the rot may begin at the tip of the ear or follow along tracks made by insect injury

PINK

Fusarium Ear and Kernel Rot

White to pink or salmon-colored cottony mold beginning on the ear; affected kernels may be scattered or clustered throughout the ear and are often tan or brown colored or have white streaks

Gibberella Ear Rot

Red or pink mold beginning at the tip of the ear; silks and husks may adhere to the ear due to excessive mold; in severe cases, the pink mold is visible on the outside of the husks at the ear tip

RED

Gibberella Ear Rot

Red or pink mold beginning at the tip of the ear; silks and husks may adhere to the ear due to excessive mold; in severe cases, the pink mold is visible on the outside of the husks at the ear tip

TAN

Fusarium Ear and Kernel Rot

White to pink or salmon-colored cottony mold beginning on the ear; affected kernels may be scattered or clustered throughout the ear and are often tan or brown colored or have white streaks

WHITE

Common Smut

Galls can form on stalks, leaves, ear, and tassels as swollen, distorted growths with a glistening white membrane that ruptures to reveal a mass of dark brown or black powdery spores; galls cause yield loss, lodging, and kernel loss

Diplodia Ear Rot

White mold on the ear turning to a grayish brown color rotting the entire ear, including kernels; mold may be apparent on the outside of the husk or on the shank; raised black bumps can usually be seen on the moldy husk or kernels

Fusarium Ear and Kernel Rot

White to pink or salmon-colored cottony mold beginning on the ear; affected kernels may be scattered or clustered throughout the ear and are often tan or brown colored or have white streaks

No Distinct Discoloration

Crazy Top

Tassel bracts may proliferate causing a very bushy appearance of the plant; internodes may be short or long, there may be a proliferation of ear shoots, leaves that are narrow and straplike, excessive tillering, or lack of ear and tassel formation