Sweet Corn Diseases and Control Measures
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Sweet Corn Diseases and Control Measures
Sweet corn is widely grown throughout New York in small to large fresh-market
commercial plantings as well as in extensive processing sweet corn acreages, and
sometimes in backyard gardens. Also important is the fact field corn is an important
row crop in New York because pathogens infecting sweet corn also infect field corn
which can be an important source for sweet corn especially of pathogens capable of
long-distance dispersal.
The diseases affecting sweet corn in New York are numerous and are caused by three
major groups of plant pathogens — bacteria, fungi, and viruses. Fourteen 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), host resistance, previous cropping histories, crop location within the state,
and availability of insect vectors. Several listed diseases rarely occur. 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 is sold treated
with a fungicide/insecticide mixture to manage seed rot and seedling blights. Most of
the diseases listed occur sometime after plant establishment. Insect pests usually are a
greater concern than diseases because several directly attack ears.
Some diseases are more important to manage in fresh-market than processing crops,
notably northern corn leaf blight and common rust, because symptoms can develop on
husks which affects marketability.
Some diseases have become more important, for example northern corn leaf blight
which is most likely due to this pathogen having evolved new virulence able to
overcome resistance used in breeding of field corn, thereby increasing amount of
inoculum of the pathogen. While other diseases have become less important because
of improved management practices, notably Stewart’s wilt for which there are now
numerous resistant varieties. It was among the more common diseases in New York.
Goss’s wilt and tar spot are two new diseases affecting sweet corn in midwestern
states to be aware of because of potential for the pathogen to spread to New York.
Because resistant varieties are an important management practice and new sweet corn
varieties are introduced each year, some with added disease resistance, it is worthwhile
each year to check the resistant sweet corn variety list and the latest seed catalogs for
up-to-date information.
The two tables below contain information about diseases that occur in New York (or
could) grouped by pathogen type and listed in order of importance:
Table 1 has relative importance of each disease in terms of occurrence and
potential severity in the absence of management.
Table 2 has plant parts affected, favorable conditions, symptoms, survival,
spread, and control measures.Sweet Corn Diseases and Casual Pathogens that can Occur in New York
Pathogen Type Occurrence Severity
& Pathogen Scientific Name
Disease Name (Rare=1 to (Slight =1 to
Common=4) Very=3)
Bacteria
• Holcus spot Pseudomonas syringae 2 1
• Stewart’s wilt Erwinia stewartia 1 1 to 2
(aka Bacterial wilt) (Pantoea stewartii)
• Goss’s bacterial wilt Clavibacter michiganensis Not detected
and blight subsp. nebraskensis
Fungi
• Northern corn leaf Exserohilum turcicum 4 1 to 3
blight (NCLB) (Setosphaeria turcica) (widespread)
• Common rust Puccinia sorghi 4 1 to 3
(widespread)
• Common smut Ustilago maydis 3 1
• Eyespot Aureobasidium zeae 2 1 to 2
(Kabatiella zeae) (farm specific)
• Gray leaf spot Cercospora zeae-maydis 2 1 to 2
(mostly western
NY)
• Carbonum leaf spot Bipolaris carbonum 1 1
(Cochliobolus carbonum)
• Head smut Sphacelotheca reiliana 1 2 to 3
• Southern leaf blight Bipolaris maydis 1 1
(SLB) (Cochliobolus (occurred
heterostrophus) recently on LI)
• Tar spot (fungus) Phyllachora maydis Not detectedViruses
• Barley yellow dwarf Barley yellow dwarf 2 1 to 2
luteovirus (BYDV) (farm specific)
• Cereal yellow dwarf
Cereal yellow dwarf
polerovirus (CYDV)
• Maize dwarf mosaic Maize dwarf mosaic 1 1
potyvirus (MDMV)
Plant
Disease and parts Conditions favorable for Symptoms and Survival
causal agent affected the disease effect of the disease and spread Control
Holcus spot Foliage, Often appears after a rain storm Round, small, white to light tan spots Bacteria over- Crop rotation and tillage to
occasionally when warm (75-86°F is favorable). on leaves. Spots typically have a winter in crop incorporate debris.
ears During storms, splashing water brown border. Yield not impacted debris. The
Pseudomonas disperses the pathogen and wounds but spots on husks can affect pathogen has a
syringae pv. that occur (such as by blowing soil) marketability. wide host range
syringae enable the pathogen to enter the including many
leaf. grasses and dicots.
Stewart’s wilt Foliage, High temp., high levels of Linear pale green to yellow streaks Bacteria over- Use resistant or tolerant
(Bacterial wilt) & stem pith, ammonium N & P, low levels of Ca with irregular or wavy margins that winter in corn flea hybrids and varieties. Early
leaf blight roots, and K increase plant susceptibility; may extend the length of the leaf. beetles; applications of insecticide to
tassels, mild winters favor survival of flea These streaks soon dry and become sometimes in control vector on susceptible
cobs, and beetles, hence increases chance of brown. Infected plants may produce kernels; dispersed varieties. Occurrence of
Erwinia stewartii kernels transmission. Abundance of premature bleached and dead tassels. by insects and, Stewart’s wilt in NY has
bacterial wilt is limited by the Internal stem discoloration seen in rarely, by seed. decreased substantially since
availability of the corn flea beetle. cross section of stem. Reduced yield these control measures became
An index of potential problems is due to reduced photosynthetic areas. available.
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.
Northern corn leaf Foliage, Moderate temp. (18-27°C) and Long elliptical (cigar shaped) On/in infected Because of race situation, use
blight (aka occasionally heavy dews; several races occur (1, grayish-green or tan lesions 2.5-15 plant debris. resistant hybrids; most resistant
northern leaf ears 2, & 3), but only 1 and 2 identified cm long. First on lower leaves, Harbored by some to race 0 but not race 1;
blight) in New York progressing upward on the plant. weeds (ex. spraying with fungicides may
Severe leaf infection causes (Johnsongrass, be necessary; eradicate weed
coalescing of lesions and gray sudangrass, etc.) hosts and plant debris.
Exserohilum appearance like frost or drought
turcicum injury. Infection during early stage of
(syn. Setosphaeria growth may cause heavy loss in ear
turcica) fill. When severe, plants are killed
prematurely.
Common rust May occur Favored by moderate temp., Develops soon after silking; oval Urediniospores White varieties generally more
on most frequent heavy dews and high pustules containing reddish-orange cause reinfection; susceptible but some yellow
plant parts nitrogen spores occur on both leaf surfaces; pustules turn hybrids equally susceptible;
Puccinia sorghi but mainly premature leaf senescence reduces black in fall with choose tolerant varieties and
on leaves yields and quality due to sugar drop. winter teliospores, consider fungicide sprays.
which infect
Oxalis (wood
sorrel) weed host;
primary inoculum
blown into north
from southern
locations.Plant
Disease and parts Conditions favorable for Symptoms and Survival
causal agent affected the disease effect of the disease and spread Control
Common smut Seedling Rain and humid weather for initial First indication as leaf infection Spores survive in Steady growth of corn reduces
infection infection, then dry, sunny weather; (small bumps) occurs in leaf whorl soil; crop rotation amount of smut; excess
rare because high N levels. stage; large, fleshy galls covered by of questionable nitrogen and mechanical
Ustilago maydis of warm silvery-white membrane ruptures to value; windblown injuries increases prevalence;
temp. expose black mass of spores; reduced spores from debris choose resistant or tolerant
requirement; yield and difficulty in handling for lodge in nodes and varieties; removal of galls
foliage, ears, processing corn is a problem. growing tips. before rupturing beneficial in
stems, and gardens
tassels are
affected
Eyespot Leaves and Cool, humid weather Small translucent, round to oval Overwinters in Use less susceptible or tolerant
leaf lesions, 1-4mm in diameter with corn debris; hybrids and varieties; use
sheathes, yellowish halos that may fuse to dispersed by wind rotation or plowing or both.
Aureobasidium outer husks, form large necrotic areas; for field and splashing rain.
zeae kernels corn rapid drying of foliage reduces
(syn. Kabatiella (when grain yield and silage quality.
zeae) severe)
Gray leaf spot Affects Prolonged periods of dew, fog and Appears as rectangular lesions, Corn is the only Hybrids differ in their
foliage some cloudy weather. which become tan and then gray in known host. susceptibility. Fall burial of
time after color. The sharp parallel edges and Common when crop residues and crop
Cercospora zeae- anthesis opacity of mature lesions are corn follows corn rotations are important.
maydis diagnostic. and diseased crop
residues remain on
the soil surface.
Anthracnose leaf Seedling High temp. & extended humid Small, oval to elongated water- On corn debris Use resistant hybrids and
blight and foliage; periods of cloudy weather; free soaked spots on leaves; the lesions and seeds and varieties; rotation important;
may also water necessary for spore are semi-transparent; spots enlarge, other grass hosts; plow down crop residue and
cause severe dispersion and germination. become tan at center with reddish- spores dispersed strive for balanced soil fertility.
Colletotrichum root & stalk brown or yellow-orange border; by wind and
graminicola rot (field diseased leaves wither and die within splashing rain or
(syn. Glomerella corn) a few days; fruiting bodies may seeds.
graminicola) develop in the lesion with dark setae.
Carbonum leaf Foliage & Moderate temperature & high Race 1: Oval to circular tan spots On many grasses Use resistant hybrids and
spot ears relative humidity; sporulates with concentric zones. and weeds; on/in varieties.
abundantly in damp weather seeds; dispersed
by wind and
(pka northern Race 2: Oblong, chocolate-colored seeds.
corn leaf spot) spots; rare; both races readily attack
ears causing a black felty mold over
the kernels.
Bipolaris
carbonum
(syn. Cochliobolus Race 3: Narrow linear lesions up to
carbonum) 15-20 cm long; lesions are grayish-
tan, surrounded by a light to darkly
pigmented border (current dominant
race in NY).
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.Plant
Disease and parts Conditions favorable for Symptoms and Survival
causal agent affected the disease effect of the disease and spread Control
Downy mildew All corn Soilborne fungus requires soil Symptoms vary but consist first of The fungus infects Provide adequate soil drainage
types moisture at the seedling stage for excessive tillering, rolling and by motile or avoid plating in low, wet
including infection to occur. twisting of upper leaves; most zoospores, which areas; crop rotation and clean
(Crazy top) sorghum; characteristic symptom is encyst on the roots plowing are only slightly
fungus proliferation of the tassel leading to a and produce germ effective control measures.
Sclerophthora infects leaf structure and suggestive of tubes. Fungus
macrospora systemically herbicide injury; this phyllody may overwinters by
at seedling also appear in the ears. oospores;
stage, but infection requires
symptoms flooded soils soon
most after planting or
obvious at before plants
top of plant reach the 4 to 5
because of leaf stage.
malformed
stalks,
shortened
internodes
and tops
Head smut All types of High concentration of teliospores, Seedling infection through rootlets or Seedborne spores Use resistant or tolerant
corn, also soil temp. of 21-28°C, and coleoptile from spores on seed or in provide initial varieties; seed treatments with
sorghum moderate to low soil moisture soil, followed by systemic inoculum, fungicides to prevent
Sphacelotheca and distribution; first symptoms when soilborne introduction; requires long
favors seedling infection; low
reiliana sudangrass, tassels emerge with each sorus teliospores rotations once teliospores occur
nitrogen levels heavy soils, slow to
from dry out in Spring; causes crusting covered by grayish-white periderm thereafter remain in soil.
seedling to and impedes emergence which ruptures to reveal dusty, black viable even
ears and teliospores; if on tassels, then almost through digestive
tassels always on ears and may cause tract of animals.
multiple ears at same or successive
nodes; ears completely converted
into fungal sori with only vascular
strands remaining
Southern leaf Foliage, Warm (20-32°C) and damp Race 0: Elongated tan lesions On/in infected Use resistant hybrids and
blight stalks, ears between veins, with buff-to-brown plant debris. varieties. Plow down crop
and cobs borders; only on leaves. Dispersed by wind debris. Use fungicides also
and/or splashing labeled for northern corn leaf
Bipolaris maydis rain. blight.
(syn. Cochliobolus Race T: Tan, spindle-shaped or
heterostrophus) elliptical lesions with yellow-green
or chlorotic halos, which turn dark
reddish-brown border. On leaves,
stalks, ears, and cobs border (this
race is no longer important)
Barley yellow Leaves Depends on the survival of specific Prominent yellow or purple Transmitted by Avoid planting corn next to
dwarf luteovirus display aphid vectors for both viruses plus coloration of leaves occurs with aphids in a overwintered small grains or
(BYDV) color occurrence in grain crops (barley, either BYDV or CYDV depending persistent manner. grass fields. Insecticides can be
symptoms; oats, wheat) and wild grasses on the particular variety infected. Requires 24-48 used to reduce secondary virus
plants and Early infection results in shortened hours for spread within the crop.
and ears are plants and ears, and blanking of the acquisition (can be
stunted if tips of ears as short at 15-30
Cereal yellow plants are min.) and then
dwarf polerovirus infected hours to circulate
(CYDV) early throughout the
aphid before aphid
can retransmit the
virusPlant
Disease and parts Conditions favorable for Symptoms and Survival
causal agent affected the disease effect of the disease and spread Control
Maize dwarf Leaves, Moderate summer temp. (18-27°C) Near the base of the youngest leaves, In many grass & Use tolerant or resistant
mosaic potyvirus leaf-sheath favor high aphid populations and irregular, light and dark green mottle weed hosts (ex. hybrids and varieties; plant
(MDMV) and ear increase spread of inoculum and mosaic patterns appear that may (Johnsongrass); early; spray insecticide to
(flag) leaves develop into narrow, light green or seedborne but rare control aphids and slow spread
and on husk; yellowish streak along the veins; and low %;
ears show plants slightly stunted and reduction carried and
poor tip fill in ear size and seed set may occur; transmitted by
and symptoms may disappear later and over 20 aphid
blanking of young leaves become yellow species,
butt sometimes from
distant sources;
virus occurs in
most areas of New
York
Goss’s bacterial Leaves, 27°C is optimal. Bacteria need Long streaks with wavy (irregular) Spread by Partially resistant hybrids;
wilt and blight husks, and wounds from sandblasting, hail or margins; initially water-soaked, then splashing water rotate; remove or bury crop
stalks other injury to infect gray, tan to light yellow. Dark green and wind; infested residue immediately after
to black irregular spots (freckles) residue; green harvest
Clavibacter form in streaks. Dried bacterial foxtail and
michiganensis exudate is common. Leaves dry up shattercane are
subsp. nebraskensis when severe. Vascular discoloration hosts; seedborne
and decay of stalk cavity occurs in but transmitted at
plants infected systemically. Plants too low frequency
can be killed to likely be
important
Tar spot Leaves, Moderate summer temp. (16-27°C), Small black, glossy stromata Spores dispersed Rotate; irrigate during day
leaf-sheath leaf wetness of at least 7 h at night, (pathogen fruiting bodies) by water and wind when afterwards leaves will dry
and husks and greater than 75% RH. resembling spots of tar form in potentially long before night; remove or bury
Phyllachora foliage and are visible on both distances; infested crop residue immediately after
maydis surfaces. They can be within brown, residue; no weed harvest
elliptic, necrotic spots (‘fisheye hosts
lesions’). Extensive necrosis leads to
leaf blight, premature senescence,
and plant death
Originally prepared for VegetableMD Online website by Thomas A. Zitter, Emeritus Professor,
PPPMB, Cornell University. Edited and updated March 2021 by Margaret Tuttle McGrath,
Associate Professor, Long Island Horticultural Research and Extension Center (LIHREC), Plant
Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, College of
Agriculture and Life Sciences, Cornell University mtm3@cornell.edu.You can also read
