Diseases By Crop
(Fact Sheets)
Photo Gallery
News Articles/ Disease Alerts
Diagnostic Keys
Virus Weed Hosts/ Rotation Lists
Resistant Varieties
Glossary of Plant Pathology Terms
Vegetable Guidelines
Vegetable IPM Links
Other Vegetable Links
Cornell Plant Disease Clinic


A Checklist of Sweet Corn Diseases and Suggested Control Measures

Thomas A. Zitter
Department of Plant Pathology
Cornell University
Ithaca, NY 14853

Sweet corn is widely grown in New York State from large, commercial fresh market acreages, to extensive processing vegetable acreages, to the ever-popular backyard garden plots.

The diseases affecting sweet corn in New York State are numerous, and are caused by three major groups of plant pathogens — bacteria, fungi, and viruses. Thirteen diseases are discussed in this report. All the diseases listed are not found every year because their occurrence is influenced by environmental factors (temperature, humidity, soil moisture), previous cropping histories, crop location within the state, and availability of insect vectors. Sweet corn is one crop where seedborne diseases are not an important factor (ex. included here are head smut and maize dwarf mosaic virus). In addition, most corn seed sold is treated with a fungicide/insecticide mixture to reduce the risk of seed rot and seedling blights. Most of the diseases discussed occur sometime after plant establishment.

This report is divided into two sections:

    1. A list of the common diseases occurring in New York and their relative importance
    2. Conditions favoring each disease, plant parts affected, and control measures

Because new sweet corn varieties are introduced each year, and some with added disease resistance, the latest seed catalogs should be checked for up-to-date information.

The Most Common Sweet Corn Plant Pathogens in New York State

Pathogen Group


Common Name

Scientific Name




(Rare=1 — Common=3)

(Very=+++ — Slight =+)


  1. Bacterial wilt
  2. (Stewart’s wilt)

Erwinia stewartii

(Pantoea stewartii)


+ to ++



  • Southern leaf blight
  • Helminthosporium maydis (Cochliobolus heterostrophus)



  • Northern leaf blight
  • Helminthosporium turcicum (Setosphaeria turcica)



  • Northern corn leaf spot
  • Helminthosporium carbonum

    (Cochliobolus carbonum)



  • Eyespot
  • Kabatiella zeae



  • Anthracnose
  • Colletotrichum graminicola



  • Gray leaf spot
  • Cercospora zeae-maydis



  • Downy mildew
  • (Crazy top)

    Sclerophthora macrospora


    + to ++

  • Corn smut
  • Ustilago maydis


    + to +++

  • Head smut
  • Sphacelotheca reiliana


    ++ to +++

  • Common corn rust
  • Puccinia sorghi


    + to +++



  • Barley yellow dwarf
  • Cereal yellow dwarf

    Barley yellow dwarf luteovirus (BYDV)

    Cereal yellow dwarf polerovirus (CYDV)


    + to ++

  • Maize dwarf mosaic
  • Maize dwarf mosaic potyvirus (MDMV)



    Disease and causal agent

    Plant parts affected

    Conditions favorable for the disease

    Appearance and
    effect of the disease

    and spread



    Bacterial wilt (Stewart’s wilt) & leaf blight

    Erwinia stewartii

    Foliage, stem pith, roots, tassels, cobs, and kernels

    High temp., high levels of ammonium N & P, low levels of Ca and K increase plant susceptibility; mild winters favor survival of flea beetles, hence increases chance of transmission. Abundance of bacterial wilt is limited by the availability of the corn flea beetle. An index of potential problems is calculated from the sum of the monthly mean temperature for the previous winter (December, January, and February). When the index exceeds 100, bacterial wilt is highly probable.

    Linear pale green to yellow streaks with irregular or wavy margins that may extend the length of the leaf. These streaks soon dry and become brown. Infected plants may produce premature bleached and dead tassels. Internal stem discoloration seen in cross section of stem. Reduced yield due to reduced photosynthetic areas.

    Bacterial over-winter in corn flea beetles; sometimes in kernels; dispersed by insects and, rarely, by seed.

    Use resistant or tolerant hybrids and varieties. Early applications of insecticide to control vector on susceptible varieties.


    Southern leaf blight

    Cochliobolus heterostrophus

    (syn. Helminthosporium)

    maydis (anamorph Bipolaris maydis)

    Foliage, stalks, ears and cobs

    Warm (20-32°C) and damp

    Race 0: Elongated tan lesions between veins, with buff-to-brown borders; only on leaves

    Race T: Tan, spindle-shaped or elliptical lesions with yellow-green or chlorotic halos, which turn dark reddish-brown border. On leaves, stalks, ears, and cobs

    On/in infected plant debris. In/on seeds (Race T). Dispersed by wind and/or splashing rain. Transmitted by infected seeds (T).

    Use corn with normal cytoplasm and resistant hybrids and varieties. Plow down crop debris. Use fungicides also labeled for Northern corn leaf blight.


    Northern leaf blight

    Setosphaeria turcica

    (syn. Helminthosporium turcicum) (anamorph Exserohilum turcicum)

    Foliage, occasionally ears

    Moderate temp. (18-27°C) and heavy dews; several races occur (1, 2, & 3), but only 1 and 2 identified in New York

    Long elliptical (cigar shaped) grayish-green or tan lesions 2.5-15 cm long. First on lower leaves, progressing upward on the plant. Severe leaf infection causes coalescing of lesions and gray appearance like frost or drought injury. Infection during early stage of growth may cause heavy loss in ear fill. When severe, plants are killed prematurely.

    On/in infected plant debris. Harbored by some weeds (ex. (Johnsongrass, sudangrass, etc.)

    Because of race situation, use resistant hybrids; most resistant to race 1 but not race 2; spraying with fungicides may be necessary; eradicate weed hosts and plant debris.


    Northern corn leaf spot

    Cochliobolus carbonum (syn. Helminthosporium carbonum)

    Foliage & ears

    Moderate temperature & high relative humidity; sporulates abundantly in damp weather

    Race 1: Oval to circular tan spots with concentric zones.

    Race 2: Oblong, chocolate-colored spots; rare; both races readily attack ears causing a black felty mold over the kernels.

    Race 3: Narrow linear lesions up to 15-20 cm long; lesions are grayish-tan, surrounded by a light to darkly pigmented border.

    Race 4: Similar to race 2, but with concentric zones of sporulation

    Race 0: Produces small flecks on immature leaves, and is not considered to be important

    On many grasses and weeds; on/in seeds; dispersed by wind and seeds.

    Use of resistant hybrids and varieties.

    Disease and causal agent

    Plant parts affected

    Conditions favorable for the disease

    Appearance and
    effect of the disease

    and spread



    Kabatiella zeae

    Leaves and leaf sheathes, outer husks, kernels (when severe)

    Cool, humid weather

    Small translucent, round to oval lesions, 1-4mm in diameter with yellowish halos that may fuse to form large necrotic areas; for field corn rapid drying of foliage reduces grain yield and silage quality

    Overwinters in corn debris; dispersed by wind and splashing rain.

    Use less susceptible or tolerant hybrids and varieties; use rotation or plowing or both.


    Anthracnose leaf blight

    Colletotrichum graminicola

    (teleomorph Glomerella graminicola)

    Seedling and foliage; may also cause severe root & stalk rot (field corn)

    High temp. & extended humid periods of cloudy weather; free water necessary for spore dispersion and germination.

    Small, oval to elongated water-soaked spots on leaves; the lesions are semi-transparent; spots enlarge, become tan at center with reddish-brown or yellow-orange border; diseased leaves wither and die within a few days; fruiting bodies may develop in the lesion with dark setae.

    On corn debris and seeds and other grass hosts; spores dispersed by wind and splashing rain or seeds.

    Use resistant hybrids and varieties; rotation important; plow down crop residue and strive for balanced soil fertility.


    Gray leaf spot

    Cercospora zeae-maydis

    Affects foliage some time after anthesis

    Prolonged periods of dew, fog and cloudy weather.

    Appears as rectangular lesions, which become tan and then gray in color. The sharp parallel edges and opacity of mature lesions are diagnostic

    Corn is the only known host. Common when corn follows corn and diseased crop residues remain on the soil surface.

    Hybrids differ in their susceptibility. Fall burial of crop residues and crop rotations are important.


    Downy mildew

    (Crazy top)

    Sclerophthora macrospora

    All corn types including sorghum; fungus infects systemically at seedling stage, but symptoms most obvious at top of plant because of malformed stalks, shortened internodes and tops

    Soilborne fungus requires soil moisture at the seedling stage for infection to occur.

    Symptoms vary but consist first of excessive tillering, rolling and twisting of upper leaves; most characteristic symptom is proliferation of the tassel leading to a leaf structure and suggestive of herbicide injury; this phyllody may also appear in the ears.

    The fungus infects by motile zoospores, which encyst on the roots and produce germ tubes. Fungus overwinters by oospores; infection requires flooded soils soon after planting or before plants reach the 4 to 5 leaf stage.

    Provide adequate soil drainage or avoid plating in low, wet areas; crop rotation and clean plowing are only slightly effective control measures.


    Disease and causal agent

    Plant parts affected

    Conditions favorable for the disease

    Appearance and

    effect of the disease


    and spread


    Common smut

    Ustilago maydis

    Seedling infection rare because of warm temp. requirement; foliage, ears, stems, and tassels are affected

    Rain and humid weather for initial infection, then dry, sunny weather; high N levels.

    First indication as leaf infection (small bumps) occurs in leaf whorl stage; large, fleshy galls covered by silvery-white membrane ruptures to expose black mass of spores; reduced yield and difficulty in handling for processing corn is a problem.

    Spores survive in soil; crop rotation of questionable value; windblown spores from debris lodge in nodes and growing tips.

    Steady growth of corn reduces amount of smut; excess nitrogen and mechanical injuries increases prevalence; choose resistant or tolerant varieties; removal of galls before rupturing beneficial in gardens


    Head smut

    Sphacelotheca reiliana

    All types of corn, also sorghum and sudangrass, from seedling to ears and tassels

    High concentration of teliospores, soil temp. of 21-28°C, and moderate to low soil moisture favors seedling infection; low nitrogen levels heavy soils, slow to dry out in Spring; causes crusting and impedes emergence

    Seedling infection through rootlets or coleoptile from spores on seed or in soil, followed by systemic distribution; first symptoms when tassels emerge with each sorus covered by grayish-white periderm which ruptures to reveal dusty, black teliospores; if on tassels, then almost always on ears and may cause multiple ears at same or successive nodes; ears completely converted into fungal sori with only vascular strands remaining

    Seedborne spores provide initial inoculum, soilborne teliospores thereafter remain viable even through digestive tract of animals.

    Resistant or tolerant varieties; seed treatments with fungicides to prevent introduction; requires long rotations once teliospores occur in soil.


    Common corn rust

    Puccinia sorhgi

    May occur on most plant parts but mainly on leaves

    Favored by moderate temp., frequent heavy dews and high nitrogen

    Develops soon after silking; oval pustules containing reddish-orange spores occur on both leaf surfaces; premature leaf senescence reduces yields and quality due to sugar drop.

    Urediniospores cause reinfection; pustules turn black in fall with winter teliospores, which infect Oxalis (wood sorrel) weed host; primary inoculum blown into north from southern locations.

    White varieties generally more susceptible but some yellow hybrids equally susceptible; choose tolerant varieties and consider fungicide sprays.


    Barley yellow dwarf luteovirus (BYDV) and Cereal yellow dwarf polerovirus (CYDV)

    Leaves display color symptoms; plants and ears are stunted if plants are infected early

    Depends on the survival of specific aphid vectors for both viruses plus occurrence in grain crops (barley, oats, wheat) and wild grasses

    Prominent yellow or purple coloration of leaves occurs with either BYDV or CYDV depending on the particular variety infected. Early infection results in shortened plants and ears, and blanking of the tips of ears

    Transmitted by aphids in a persistent manner. Requires 24-48 hours for acquisition (can be as short at 15-30 min.) and then hours to circulate throughout the aphid before aphid can retransmit the virus

    Avoid planting corn next to overwintered small grains. Insecticides can be used to reduce secondary virus spread within the crop.


    Disease and causal agent

    Plant parts affected

    Conditions favorable for the disease

    Appearance and

    effect of the disease


    and spread


    Maize dwarf mosaic potyvirus (MDMV)

    Leaves, leaf-sheath and ear (flag) leaves and on husk; ears show poor tip fill and blanking of butt

    Moderate summer temp. (18-27°C) favor high aphid populations and increase spread of inoculum.

    Near the base of the youngest leaves, irregular, light and dark green mottle and mosaic patterns appear that may develop into narrow, light green or yellowish streak along the veins; plants slightly stunted and reduction in ear size and seed set may occur; symptoms may disappear later and young leaves become yellow

    In many grass & weed hosts (ex. (Johnsongrass); seedborne but rare and low %; carried and transmitted by over 20 aphid species, sometimes from distant sources; virus occurs in most areas of the State

    Use of tolerant or resistant hybrids and varieties; plant early; spray insecticide to control aphids and slow spread