Maize Diseases:A Guide for FieldIdentification

4th edition

The CIMMYT Maize Program

CIMMYT® (www.cimmyt.org) is an internationally funded, not-for-profit organization that conducts research and training related tomaize and wheat throughout the developing world. Drawing onstrong science and effective partnerships, CIMMYT works to create,share, and use knowledge and technology to increase food security,improve the productivity and profitability of farming systems, andsustain natural resources. Financial support for CIMMYT’s work comesfrom many sources, including the members of the Consultative Groupon International Agricultural Research (CGIAR) (www.cgiar.org),national governments, foundations, development banks, and otherpublic and private agencies.

© International Maize and Wheat Improvement Center (CIMMYT)2004. All rights reserved. The designations employed in thepresentation of materials in this publication do not imply theexpression of any opinion whatsoever on the part of CIMMYT or itscontributory organizations concerning the legal status of any country,territory, city, or area, or of its authorities, or concerning thedelimitation of its frontiers or boundaries. CIMMYT encourages fairuse of this material. Proper citation is requested.

Correct citation: The CIMMYT Maize Program. 2004.Maize Diseases: A Guide for Field Identification. 4th edition.Mexico, D.F.: CIMMYT.

Abstract: Intended for field use by agricultural technicians and maizefarmers, this pocket-size manual carries descriptions and colorphotographs for more than 50 fungal, bacterial, viral, and mollicutediseases that affect the maize crop worldwide, with basic informationon pathogens and symptoms. A diagnostic key facilitates quickidentification of diseases and their effects. In this fourth edition,nomenclature has been updated, new diseases and informationadded, and improved photographs included.

ISBN: 970-648-109-5AGROVOC descriptors: Plant diseases; Zea mays; Bacterialdiseases; Viruses; Fungi disease; Mildews; Leaf area; Fusarium; Smuts;Rots; Penicillium; Charcoal; Nigrospora; Cephalosporium; Kernels;Botryodiplodia; Dwarfism; NecrosisAGRIS category codes: H20 Plant Diseases; F01 Crop HusbandryDewey decimal classification: 633.15

Printed in Mexico.

Contents

Introduction ........................................................... 1

Diseases caused by fungi: Foliar diseasesBrown spot ............................................................................... 2Downy mildews ...................................................................... 5Common rust .......................................................................... 9Polysora rust ............................................................................ 10Tropical rust ............................................................................. 10Borde blanco, Vertical banded blight ........................... 13Tar spot complex ................................................................... 14Turcicum leaf blight ............................................................. 17Maydis leaf blight .................................................................. 18Carbonum leaf spot .............................................................. 21Anthracnose leaf blight ...................................................... 22Yellow leaf blight ................................................................... 25Banded leaf and sheath blight ........................................ 26Leptosphaeria leaf spot ...................................................... 29Phaeosphaeria leaf spot ..................................................... 29Hyalothyridium leaf spot ................................................... 30Curvularia leaf spot .............................................................. 33Gray leaf spot .......................................................................... 34Zonate leaf spot ..................................................................... 37Septoria leaf blotch .............................................................. 38Eyespot ....................................................................................... 41Macrospora leaf stripe ......................................................... 42

Diseases caused by fungi: Stalk rots and smutsPythium stalk rot ................................................................... 45Fusarium and gibberella stalk rots ................................ 46Head smut ................................................................................ 49False head smut ..................................................................... 50Black bundle disease and late wilt ................................ 53Anthracnose stalk rot .......................................................... 54Charcoal stalk rot ................................................................... 57Botryodiplodia stalk rot ...................................................... 58Stenocarpella stalk rot ........................................................ 61

Diseases caused by fungi: Ear rotsPenicillium ear rots ............................................................... 63Aspergillus ear rots ............................................................... 64Fusarium and gibberella ear rots ................................... 67Ergot, horse’s tooth ............................................................... 68Charcoal ear rot ...................................................................... 71Nigrospora ear rot ................................................................. 72Gray ear rot .............................................................................. 75Common smut ........................................................................ 76Botryodiplodia or black kernel rot ................................ 79Cephalosporium kernel rot ............................................... 80Hormodendrum ear rot ...................................................... 80Stenocarpella ear rot ........................................................... 83

Diseases caused by bacteriaBacterial stalk rot ................................................................... 84Stewart’s wilt ........................................................................... 87Bacterial leaf stripe ............................................................... 88

Diseases caused by viruses and mollicutesMaize chlorotic dwarf virus (MCDV) ............................. 91Maize chlorotic mottle virus (MCMV) ........................... 92Maize dwarf mosaic virus (MDMV) ............................... 95Sugarcane mosaic virus (SCMV) ..................................... 95Maize lethal necrosis (MLN) .............................................. 96Maize mosaic virus I (MMV) ............................................. 99Maize stripe virus (M StV) ................................................. 100Maize streak virus (MSV) .................................................... 103Maize rough dwarf virus (MRDV) ................................... 104Maize fine stripe virus ......................................................... 107Maize bushy stunt (MBS) ................................................... 108Corn stunt ................................................................................. 111Diagnostic key ........................................................................ 112

Contents

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Introduction

This popular booklet, already in its fourth edition, isdesigned as a quick guide for identifying maize diseases.Based on previous editions produced by CIMMYT maizepathologist Carlos De Leon, the new work has beenupdated by contributions from CIMMYT maize pathologistDan Jeffers. It is intended for field use by agriculturaltechnicians and maize producers, and the taxonomic shortforms of the various pathogens are deemed to beappropriate and adequate. For fungal pathogens, both thesexual (teleomorph) and asexual (anamorph) names of thefungi are often included. Several modifications innomenclature have been made since the last edition.Common names of the diseases are designated mostlyfollowing the nomenclature described by A.J. Ullstrup (1985.Plant Disease 69:658-659). The text comprises a briefdescription of common maize diseases, their causal agents,and their symptoms. Additional diseases and newinformation have been included, based on advances inscience since the previous edition. There are numerouscolor photographs of diseased plants. A diagnostic key isincluded as an appendix. The text is divided according tothe four causal agents for maize diseases: fungi, bacteria,viruses, and mollicutes. Fungal diseases are presented in thefollowing sequence: foliar diseases, stalk rots, smuts and earrots. Most diseases covered are economically significant orhave the potential to become so.

We greatly appreciate the editorial assistance of CIMMYTscience writer, Mike Listman, and the production anddesign skills of CIMMYT designer, Wenceslao Almazán, inproducing this new edition.

First edition: 1974Second edition: 1978Third edition: 1984Fourth edition: 2003

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Brown spotPhysoderma maydis

The disease normally occurs in areas of highrainfall and high mean temperatures. It attacksleaves, leaf sheaths, stalks, and sometimes outerhusks.

The first noticeable symptoms develop on leafblades and consist of small chlorotic spots,arranged as alternate bands of diseased andhealthy tissue (Photo 1). Spots on the mid-ribsare circular and dark brown, while lesions onthe laminae continue as chlorotic spots. Nodesand internodes also show brown lesions. Insevere infections, these may coalesce andinduce stalk rotting and lodging (Photo 2).

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Downy mildews

Several species of the genera Peronosclerospora,Sclerospora, and Sclerophthora are responsible fordowny mildews:

Crazy top downy mildewSclerophthora macrospora

Brown stripe downy mildewSclerophthora rayssiae var. zeae (Photo 3)

Green ear diseaseSclerospora graminicola

Java downy mildewPeronosclerospora maydis (Photo 4)

Philippine downy mildewPeronosclerospora philippinensis (Photo 5)

Sugarcane downy mildewPeronosclerospora sacchari (Photo 6)

Sorghum downy mildewPeronosclerospora sorghi (Photos 7, 8, 9)

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These diseases are of serious concern to maizeproducers in several countries of Asia, Africa, andthroughout the Americas. Symptom expression isgreatly affected by plant age, pathogen species, andenvironment. Usually, there is chlorotic striping orpartial symptoms in leaves and leaf sheaths, alongwith dwarfing. Downy mildew becomes conspicuousafter development of a downy growth on or underleaf surfaces. This condition is the result of conidiaformation, which commonly occurs in the earlymorning.

The diseases are most prevalent in warm, humidregions. Some species causing downy mildew alsoinduce tassel malformations, blocking pollenproduction and ear formation. Leaves may benarrow, thick, and abnormally erect.

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Maize rusts

The three leaf rusts on maize are common rust,polysora rust, and tropical rust.

Common rustPuccinia sorghi

The disease is found worldwide in subtropical,temperate, and highland environments with highhumidity.

Common rust is most conspicuous when plantsapproach tasseling. It may be recognized by small,elongate, powdery pustules over both surfaces of theleaves (Photo 10). Pustules are dark brown in earlystages of infection; later, the epidermis is rupturedand the lesions turn black as the plant matures.Plants of the alternate host (Oxalis spp.) arefrequently infected with light orange coloredpustules (Photo 11). This is simply another stage ofthe same fungus.

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Polysora rustPuccinia polysora

Pustules are smaller, lighter in color (light orange), andmore circular (Photo 12) than those produced byP. sorghi. They are also present on both leaf surfaces,but the epidermis remains intact longer than it does inP. sorghi-infected leaves. Pustules turn dark brown asplants approach maturity. No alternate host of thefungus is known. Polysora rust (or southern rust) iscommon in hot and humid lowland tropical conditions.

Tropical rustPhysopella zeae

Outbreaks of this rust are sporadic and confined to theAmerican tropics.

Pustules vary in shape from round to oval. They aresmall and found beneath the epidermis. At the centerof the pustule the lesion appears white to pale yellowand an opening develops (Photo 13). The pustule issometimes black rimmed, but its center remains light.No alternate host of the fungus is known.

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Borde blanco,Vertical banded blightMarasmiellus paspali var. americanus,M. paspali var. paspali, M. paspali sensu lato

Symptoms on the foliage are very similar to thoseproduced by banded leaf and sheath blight (BLSB;see page 27). The disease has been reported onmaize growing in hot, humid, lowland tropical areas,where it causes no economic damage.

Elongated, concentric bicolored lesions startdeveloping on margins of the leaves (Photo 14)around flowering time. At this stage, there are noapparent symptoms of fungal growth on the lesions.Later in the season, small fungal fructificationsresembling sclerotia of the causal agent of BLSB willdevelop. However, on closer inspection thesestructures are agaricoid fructifications (basidiomata)of the fungus (Photo 15). High humidity and rainfallfavor the development of these ephemeralstructures.

The three above-mentioned species have beenreported on maize in tropical American countries,East and Southeast Asia, and West African countries,respectively.

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Tar spot complexPhyllachora maydis and Monographella maydis

The disease occurs in relatively cool, humid areasin the tropics, similar to the conditions whereturcicum leaf blight is prevalent. Characteristicblack, raised, shiny spots are initially produced(Photo 16). Infected foliar tissue will becomenecrotic and die.

In several countries in the Americas, a secondpathogen, Monographella maydis, has beenassociated with Phyllachora maydis as part of the“tar spot complex.” This association results in thedevelopment of necrotic tissue around the tarspot (Photo 17). These necrotic lesions maycoalesce, causing a complete burning of thefoliage. Lesions caused by M. maydis alone areround and 5-6 cm in diameter (Photo 18).

Lesions of both pathogens involved in the tarspot complex start developing in the lowerleaves before flowering time. In favorableconditions, the infection spreads to the youngerleaves. Affected ears are light in weight withloose kernels. Many kernels at the tip of the earwill show premature germination while still onthe cob (Photo 19).

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Turcicum leaf blightTeleomorph: Setosphaeria turcica(syn. Trichometasphaeria turcica)(Anamorph: Exserohilum turcicum, syn.Helminthosporium turcicum)

An early symptom is the easily recognized, slightlyoval, water-soaked, small spots produced on theleaves. These grow into elongated, spindle-shapednecrotic lesions (Photo 20). They may appear first onlower leaves and increase in number as the plantdevelops, and can lead to complete burning of thefoliage.

Turcicum leaf blight (or northern leaf blight) occursworldwide and particularly in areas where highhumidity and moderate temperatures prevail duringthe growing season. When infection occurs prior toand at silking and conditions are optimum, it maycause significant economic damage.

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Maydis leaf blightTeleomorph: Cochliobolus heterostrophus(Anamorph: Bipolaris maydis, syn. Helminthosporiummaydis)

Young lesions are small and diamond shaped. Asthey mature, they elongate. Growth is limited byadjacent veins, so final lesion shape is rectangularand 2 to 3 cm long. Lesions may coalesce, producinga complete burning of large areas of the leaves(Photo 21).

The symptoms described above correspond to the“O” strain of the fungus. In the early 1970s the “T”strain caused severe damage to maize cultivars inwhich the Texas source of male sterility had beenincorporated. Lesions produced by the T strain(Photo 22) are oval and larger than those producedby the O strain. A major difference is that the Tstrain affects husks and leaf sheaths, while the Ostrain normally does not.

Maydis leaf blight (or southern maize leaf blight) isprevalent in hot, humid, maize-growing areas. Thefungus requires slightly higher temperatures forinfection than E. turcicum; however, both species areoften found on the same plant.

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Carbonum leaf spotTeleomorph: Cochliobolus carbonum(Anamorph: Bipolaris zeicola, syn. Helminthosporiumcarbonum)

This disease is most common in very moist areaswith moderate temperatures.

Different symptoms are produced on the leaves bythe five known races of the fungus. Race 1 producesoval, zonate, brownish lesions on all parts of theplants including the ears, which rot and turn black.Race 2 produces brown, slender, elongated lesions,mostly in the lower leaves (Photo 23), and can alsoproduce ear rot. Race 3 produces narrow, grayishlesions with a chlorotic border. Race 4 produceslesions similar to those from Race 2, but theyfrequently show concentric patterns. Race 5 producesonly small necrotic flecks on immature leaves.

Ear rot symptoms produced by Races 1 and 2 arevery similar.

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Anthracnose leaf blightAnamorph: Colletotrichum graminicola(Teleomorph: Glomerella graminicola)

The disease is present in warm, humid environmentsworldwide, with a foliar disease phase and a stalk-rotting phase.

The foliar infection phase of the fungus is notreported to be of economic importance in maize. Themost severe damage is caused by the stalk rot phase.Foliar damage can be observed at different stages ofplant development. In the early seedling stage, leavesshow irregular, oval-to-elongated lesions withcharacteristic, yellow-to-reddish-brown margins (Photo24). In later stages of plant development, similarlesions can be observed in the upper leaves ofinfected plants, especially in those where stalk rotsymptoms have already developed.

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Yellow leaf blightAnamorph: Phyllosticta maydis(Teleomorph: Mycosphaerella zeae-maydis)

In 1970 the disease was associated with susceptibilityin Texas male sterile cultivars, and several researcherslinked this disease with yield losses and increasedlodging. Humid, warm weather favors diseasedevelopment.

Young, diseased plants show symptoms similar to thoseobserved in nitrogen deficient plants. In mature plants,lesions are narrow, necrotic, and parallel to the veins,although not limited by them (Photos 25, 26). In olderleaves, lesions develop further and produce acharacteristic blighting near the tip.

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Banded leaf and sheath blightAnamorph: Rhizoctonia solani f. sp. sasakii(Teleomorph: Corticium sasakii, syn. Thanatephoruscucumeris)

True to the name, this disease develops on leaves andsheaths. Symptoms are characteristic concentric spotsthat cover large areas of infected leaves and husks(Photos 27, 28).

The main damage in the humid tropics is a brownishrotting of ears, which show conspicuous, light brown,cottony mycelium with small, round, black sclerotia.

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Leptosphaeria leaf spotLeptosphaeria michotii

This disease has been reported in high, humid areasof the Himalayas. Other species of Leptosphaeria thatproduce different symptoms on maize leaves areknown in other regions of the world.

Symptoms consist of small lesions that become largeand concentric, covering large areas of the leaves(Photo 29). It is most conspicuous on lower leaves atflowering.

Phaeosphaeria leaf spotPhaeosphaeria maydis

This disease is found in Brazil, Colombia, Ecuador,northern India, eastern and southern Africa, the USA,and Mexico, where Exserohilum turcicum is alsoprevalent. Conditions of high humidity and relativelylow night temperatures favor development. Lesionsappear as small pale green areas, which later becomebleached and finally necrotic, surrounded by darkbrown margins (Photo 30). Spots on leaves are roundto slightly elongated.

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Hyalothyridium leaf spotAnamorph: Hyalothyridium maydis(Teleomorph: Leptosphaerulina sp.)

This is a foliar disease reported in Colombia, CostaRica, Ecuador, and Mexico. The disease may causesevere losses in commercial plantings whenconditions are hot and humid, with cool nights.Lesions start in bottom leaves as small round freckleswhen plants are hip-high. Three weeks afterflowering, lesions turn round, brown, necrotic and are3-4 cm in diameter, showing concentric ringssurrounded by chlorotic tissue (Photos 31, 32).

In Colombia a teleomorph stage Leptosphaerulina sp.has been associated with the disease during laterstages of infection.

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Curvularia leaf spotCurvularia lunata, C. pallescens, and C. maculans

These fungi produce small necrotic or chloroticspots with a light colored halo (Photo 33).Lesions are about 0.5 cm in diameter when fullydeveloped. The disease is prevalent in hot,humid maize areas and can damage the cropsignificantly.

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Gray leaf spotCercospora zeae-maydis, C. sorghi var. maydis

This disease, also known as cercospora leaf spot, mayoccur in subtropical and temperate, humid areas.Lesions begin as small, regular, elongated brown-graynecrotic spots growing parallel to the veins (Photo34). Occasionally, lesions may reach 3.0 x 0.3 cm.Minimum tillage practices have been associated withan increased incidence of GLS. The disease is ofconcern in South America and eastern and southernAfrica. Development is favored by extended periodsof leaf wetness and cloudy conditions, and can resultin severe leaf senescence following flowering and inpoor grain fill.

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Zonate leaf spotGloeocercospora sorghi

Zonate leaf spot is more commonly found insorghum than maize.

The disease is characterized by small necroticlesions that enlarge and produce large, concentric,necrotic rings (Photo 35). Lesions may be as largeas 5 to 6 cm in diameter, and occur mainly onolder leaves.

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Septoria leaf blotchSeptoria maydis

The spotting mainly affects maize grown in cool,humid environments.

Symptoms first appear as small, light-green-to-yellowspots on the leaves (Photos 36, 37). Lesions coalesceand produce severe blotching and necrosis of affectedareas where many black, spore-producing structuresknow as pycnidia appear.

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EyespotKabatiella zeae (syn. Aureobasidium zeae)

Commercial plantings in countries with cool,moist environments may be affected by eyespot.

The disease is characterized by small (1 to 4mm), round, translucent lesions. Tan coloredcenters develop, surrounded by black-to-purplerings, with a yellow halo around them, thusproducing the characteristic “eyespot”(Photos 38, 39).

These symptoms are easily confused withphysiological or genetic spots, which are non-infectious but widely observed in maize leaves.The symptoms are also similar to early spottinginduced by Curvularia.

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Macrospora leaf stripeStenocarpella macrospora, syn. Diplodia macrospora

This disease has not been reported to causeeconomic damage, but causes some damage incommercial maize plantings in hot, humid areas.Stenocarpella macrospora is mostly an ear-rottingagent, but under appropriate climatic conditionscan cause foliar damage.

Symptoms consist of necrotic lesions along theveins. These lesions resemble spotting producedby bacteria or by Exserohilum turcicum leafblight). However, when held against the light,S. macrospora lesions exhibit a distinct narrowyellow margin not present in lesions caused byother pathogens (Photo 40). Under humidconditions, the black, spore-producing pycnidiaformed in the necrotic lesions ooze spores in fineblack threads and the lesion splits (Photo 41).

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Pythium stalk rotPythium aphanidermatum, Pythium spp.

Pythium species cause stalk rots, seed rots, andseedling blights. The disease is present in some hotand humid tropical and subtropical zones and intemperate regions.

Usually the basal internodes become soft, water-soaked, and dark, causing lodging. Damagedinternodes commonly twist before the plants lodge.Diseased plants can remain alive until all vascularbundles become affected (Photo 42).

Isolations in culture media are necessary todifferentiate Pythium from Erwinia stalk rots.

Plants can be affected prior to flowering.

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Fusarium and gibberella stalk rotsFusarium moniliforme syn. Fusarium verticillioides(Teleomorph: Gibberella fujikuroi)

Gibberella zeae (Anamorph: Fusarium graminearum)

These two species of Fusarium are responsible for stalkrots in maize:

Fusarium moniliforme is most common in dry, warmareas. It is particularly severe if it begins just beforetasseling (Photo 43).

Gibberella zeae is prevalent in cool regions. It is one ofthe most potentially damaging stalk-rotting agents(Photo 44).

Symptoms produced by these pathogens resemblethose caused by Stenocarpella or Cephalosporium, andcannot be differentiated until spore-producingstructures are observed. Wilted plants remain standingwhen dry, and small, dark-brown lesions develop in thelowest internodes. When infected stalks are split, thephloem appears dark brown, and there is a generalconspicuous browning of tissues.

In the final stages of infection, pith is shredded andsurrounding tissues become discolored.

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Head smutSphacelotheca reiliana

Head smut can cause significant economicdamage in dry, hot maize growing areas, aswell as in midhill zones and under temperateconditions.

The infection is systemic: the funguspenetrates the seedlings and grows inside theplant without showing symptoms, until thetasseling and silking stages.

The most conspicuous symptoms are (a)abnormal development of the tassels, whichbecome malformed and overgrown (Photo45); (b) black masses of spores that developinside individual male florets; and (c) massesof black spores in place of the normal ear,leaving the vascular bundles exposed andshredded (Photo 46).

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False head smutUstilaginoidea virens

False head smut occurs very rarely in hot, dry orhumid areas. The fungus commonly infects riceflowers more than maize.

Symptoms differ from those of other smuts ofmaize. False head smut produces neither tasselmalformation nor ear infection, as does truehead smut (Sphacelotheca reiliana); only a fewisolated male florets in the tassel show dark-green masses of spores (sori; Photo 47). Falsehead smut also differs from common smut(Ustilago maydis) in that no galls are produced.

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Black bundle disease and late wiltAcremonium strictum(syn. Cephalosporium acremonium) and C. maydis

Black bundle disease is caused by Cephalosporiumacremonium and is widely distributed. The late wiltdisease, caused by C. maydis, has been reported only inEgypt and India. Both diseases kill the plants nearflowering time (Photo 48). They are most common inhumid, heavy soils in hot areas. The pathogens aresoil- and seed-borne.

Infected plants do not show symptoms until they reachtasseling stage and start wilting, generally beginningfrom the top leaves. Diseased plants produce onlynubbins or ears with underdeveloped, shrunkenkernels. When split, diseased stalks show brownvascular bundles starting in the underground portionof the roots (Photo 49). Similar symptoms may beobserved in plants damaged by Fusarium moniliforme.

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Anthracnose stalk rotAnamorph: Colletotrichum graminicola(Teleomorph: Glomerella graminicola)

The fungus Colletotrichum graminicola causes both astalk rot and a leaf blight. The stalk rot is foundmostly in warm, humid areas throughout the world.Infection symptoms are clearly evident as narrow,elongated dark lesions (initially brown; turning laterto black) along the stem surface beginning whenplants approach flowering (Photo 50). In infectedplants, there is premature wilting due to thecomplete destruction of pith tissue, with shreddedvascular bundles turning dark brown (Photo 51).Because this and other fungi overwinter in infectedmaize tissues, conservation agriculture practicesinvolving mulches reportedly increase the incidenceof the disease.

(Photo courtesy of Dr. R. Carvalho)

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Charcoal stalk rotMacrophomina phaseolina

Charcoal stalk rot is most common in hot, dryenvironments. Incidence increases rapidly whendrought and high temperatures prevail neartasseling stage.

The pathogen invades seedling roots. Afterflowering, initial symptoms are the abnormaldrying of upper leaf tissue. When plants approachmaturity, the internal parts of stems show a blackdiscoloration and vascular bundles shred (Photo52), mainly in lower stalk internodes. Carefulexamination of rind and vascular bundles revealssmall, black, fungal structures known as sclerotia(Photo 53) that can overwinter and infect the nextcrop. The fungus may also infect kernels,blackening them completely.

Many crops can serve as hosts for this pathogen.

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Botryodiplodia stalk rotBotryodiplodia theobromae

The disease was first reported in India, but has beenfound in several other countries in Asia, Africa, andthe Americas. It develops in hot, humid environments.

Diseased plants dry prematurely. Splitting stalks openwill show some shredding of the pith and a dark grayto black discoloration of the vascular bundles.Abundant grayish mycelia are conspicuous in therotten areas, confined mostly to the lower internodesabove ground (Photo 54).

Unlike charcoal rot, Botryodiplodia stalk rot does notproduce black pinhead-like sclerotia in the rottenareas, but it does produce abundant, gray-blackish,cottony mycelium in cavities formed in the pith ofaffected internodes.

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Stenocarpella stalk rotStenocarpella maydis, syn. Diplodia maydisS. macrospora, syn. D. macrospora

Stalk rot is caused by S. maydis in cool, humidtemperate areas, and by S. macrospora in warm,humid zones. In susceptible cultivars it causesbrowning of the pith of basal internodes (Photos55, 56). Stalks are weakened and break easily duringstrong winds and rains. Late in the season, the mostconspicuous symptom is the abundant formation ofspore structures known as pycnidia on the surfaceof internodes where rotting has occurred.

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Penicillium ear rotsPenicillium spp.

Damage is most frequently caused by Penicilliumoxalicum, but other species may occasionally beinvolved. In many instances infection follows eardamage by insects.

A conspicuous, light blue-green powder growsbetween kernels and on the cob surface(Photos 57, 58). Kernels with fungal growthnormally become bleached and streaked.

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Aspergillus ear rotsAspergillus flavus, Aspergillus spp.

The disease may be a serious problem wheninfected ears are stored at high moisturecontents. Several species of Aspergillus can infectmaize in the field. Aspergillus niger is the mostcommon; it produces black, powdery massesof spores that cover both kernels and cob. Incontrast, A. glaucus, A. flavus (Photo 59), andA. ochraceus normally form yellow-green massesof spores. Aspergillus parasiticus is ivy green andless common in maize.

Aspergillus flavus and A. parasiticus producemycotoxins known as aflatoxins that are harmfulto birds and mammals.

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Fusarium and gibberella ear rots

Fusarium graminearum (syn. F. roseum)(Teleomorph: Gibberella zeae)

Fusarium moniliforme, syn. F. verticillioides(Teleomorph: Gibberella fujikuroi)

In maize, these two species of fungi cause ear rots,stalk rots, and seedling blights. Gibberella zeae, thesexual stage of the pathogen, is most common in cooland humid areas. Ear infection begins as whitemycelium moving down from the tip, which later turnsreddish-pink, in infected kernels (Photo 60). The fungusproduces mycotoxins—known as deoxynivalenol,zearalenone, and zearalenol—which are noxious toseveral animal species.

Fusarium moniliforme ear rot is likely the mostcommon pathogen of maize ears throughout theworld. In contrast to damage from G. zeae, that from F.moniliforme occurs mainly on individual kernels or onlimited areas of the ear (Photos 61, 62). Infectedkernels develop a cottony growth or may developwhite streaks on the pericarp and germinate on thecob. Ears infested by earworms are usually infectedwith F. moniliforme. The fungus produces mycotoxinsknown as fumonisins, which are harmful to severalanimal species.

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Ergot, horse’s toothClaviceps gigantea

This disease (anamorph Sphacelia sp.) is endemic tocertain high, cool, humid areas of the central plateauof Mexico. Infected kernels grow into large fungalstructures known as sclerotia along with normalhealthy kernels (Photo 63). In early stages ofinfection, sclerotia are pale colored, soft and slimy,finally hardening toward harvest time. These sclerotiado not produce the black powder characteristic ofcommon smut. When sclerotia are dropped on theground, they germinate and develop many head-likestructures (stromata) that release new spores whenthe maize plants silk the following season (Photo 64).

The pathogen is closely related to the fungus thatcauses ergot of rye, and also produces toxic alkaloids.

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Charcoal ear rotMacrophomina phaseolina

Like charcoal stalk rot (see page 57), the diseasecan be found in hot, humid areas with dryperiods, mainly during flowering time. At harvestkernels are pale yellow with black streaking belowthe pericarp, and the ear is loose and chaffy.Kernels are easily removed from the cob, and theyshow small, round, black, pinhead-like sclerotia onthe surface (Photos 65-67).

Plants affected by charcoal stalk rot do notnecessarily develop ear rot from the same pathogen.

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Nigrospora ear rotAnamorph: Nigrospora oryzae(Teleomorph: Khuskia oryzae)

The disease is widely distributed, and the causalfungus normally overwinters on plant residues.

Infected ears are chaffy and lightweight. Kernels arediscolored and easily removed from the cob. Underclose examination, cob tissues and kernel tips showsmall black masses of spores (Photos 68, 69).

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Gray ear rotPhysalospora zeae (syn. Botryosphaeria zeae)(Anamorph: Macrophoma zeae)

Hot, humid weather for several weeks after floweringfavors development of this ear rot. Early symptomsare very similar to those caused by stenocarpella earrot, where a white-gray mycelium develops betweenkernels and husks, which become bleached and gluedtogether. In the later stages of infection, the two fungican be readily identified:

(a) Gray ear rot. Ears have a distinct black color; themycelium is also dark and develops smallsclerotia (specks) scattered throughout the cob(Photo 70, courtesy Dr. A. J. Ullstrup).

(b) Stenocarpella ear rot (see page 83). The ear isgray-brown and the mycelium is white, withsmall black pycnidia on the cob and kernels.

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Common smutUstilago maydis

Common smut occurs throughout most maizegrowing regions, but can be more severe inhumid, temperate environments than in hot,humid, tropical lowlands.

The fungus attacks ears, stalks, leaves, andtassels (Photos 71-73). Conspicuous closed whitegalls replace individual kernels. In time the gallsbreak down and release black masses of sporesthat will infect maize plants the followingseason. The disease is most severe in young,actively growing plants and may stunt orkill them.

This is easily distinguished from head smut bythe lack of host vascular bundles that appearas fibers in smut-infected ears.

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Botryodiplodia or black kernel rotBotryodiplodia theobromae

The disease has been reported in India, Nigeria,Pakistan, and Thailand, and to a lesser extent in theAmericas. The same fungus can produce stalk rotwith a conspicuous black discoloration in moist,hot environments (see page 58).

Affected ears develop deep black, shiny kernels(Photos 74, 75), and husk leaves can also turn blackand be shredded.

There are no reports of economic losses from this disease.

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Cephalosporium kernel rotAcremonium strictum(syn. Cephalosporium acremonium)

This disease is common in hot, lowland tropical andsubtropical areas. Infected kernels show white streaksin the pericarp (Photo 76). The symptoms are similarto those of kernels infected by Fusarium moniliforme.

Hormodendrum ear rotHormodendrum cladosporoides(syn. Cladosporium cladosporoides), C. herbarum

There are no reports of economic losses fromthis disease.

Dark brown-green streaks on kernels start at thekernel and cob bases. When damage is complete, earslook dark and lightweight (Photo 77). In someinstances, fungal penetration results from physicalinjury to kernel tips.

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Stenocarpella ear rotStenocarpella maydis, syn. Diplodia maydis, S.macrospora, syn. D. macrospora

Stenocarpella ear rots are commonly found in hot,humid maize-growing areas.

Maize ears show characteristic development ofirregular bleached areas on husks. These areasenlarge until the husks become completely dried,although the plant is still green. If husks areremoved, ears appear chaffy and bleached, with awhite, cottony growth between the kernels (Photo78). Late in the season, many small, black pycnidiaform on kernels and cob tissues (Photo 79). Thesepycnidia serve as sources of inoculum for thefollowing season’s crop. Microscopic observation ofthe spores is the only way to identify whichpathogen is present.

Severely infected ears are very light. Infection morefrequently occurs through the shank and movesfrom the cob to the kernels. Stem borer injury inthe ear often increases incidence of this disease.Stenocarpella maydis produces the mycotoxindiplodiatoxin and S. macrospora produces diplodiol,both harmful to birds.

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Bacterial stalk rotErwinia chrysanthemi pv. zeae, syn. Erwinia carotovoraf. sp. zeae

This pathogen appears in areas with hightemperatures and high relative humidity. It spreadsrapidly in the host plant and quickly kills it.

Infected plants show a dark color and water soakingat the base of the stalk (Photos 80, 81) and lodge,dying shortly after tasseling.

The bacterial decomposition produces acharacteristic, unpleasant odor.

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Stewart’s wiltErwinia stewartii, syn. Pantoea stewartii

The pathogen is reportedly transmitted by maizeflea beetles (Chaetocnema pulicaria) and also atvery low frequency through infected seed. Withearly infection, lesions are first water-soaked,turning long and pale yellow with irregularmargins running the length of the leaves (Photo82). Infection may move into the stem, causing ageneral stunting, wilting, and plant death. Severelyinfected plants that set seed develop smallnubbins with few kernels. Late infection can causesevere leaf necrosis but does not lead to wilting(Photo 83).

Feeding wounds from the insect vector serve aspoints of entry for the pathogen, which is carriedfrom one season to the next by the flea beetle.

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Bacterial leaf stripePseudomonas rubrilineans, syn. P. avenae, Acidvoraxavenae subsp. avenae

No substantial crop damage has been reportedfrom this disease, although it may be of concernwhere susceptible germplasm is being utilized incertain hot and humid areas.

Bacterial stripe affects susceptible maize plantsfrom seedling to post-flowering stages. Leavesdevelop several small, pale-green lesions. Underoptimum weather conditions, lesions expandalong veins producing a conspicuous striping,mainly in the youngest leaves; stripes later dryand brown (Photo 84), often with shredding ofthe infected leaf tissue. Severe damage of thetop leaves results in tassel rotting, when deadleaves enclose the tassel (Photo 85).

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Maize chlorotic dwarf virus (MCDV)

Infected plants initially show small chlorotic spotsdeveloping later into a general chlorosis in the whorlleaves (Photo 86). Plants become stunted due toshortening of internodes, and leaves may becomereddish late in the season, resembling the reddeningsymptoms caused by corn stunt and maize bushy stunt.MCDV is transmitted by the leafhoppers Graminellanigrifrons and G. sonora for an extended period of timeafter they have fed on infected plants. Johnsongrassserves as a reservoir host for the virus and the vectorwhen maize is not being grown. So far this disease hasbeen found only in the continental United States, butprobably has a wider distribution.

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Maize chlorotic mottle virus (MCMV)

In early stages, the youngest leaves show fine chlotoricspots that coalesce and develop into broad chloroticstripes along the veins. These chlorotic stripes contrastwith dark green tissue when observed against the light(Photos 87, 88). Leaves showing chlorosis finally die.Plants are stunted because of shortened internodes.Infected plants produce fewer and smaller ears. In mostcases, the male inflorescence is malformed.

The virus is transmitted mainly by several chrysomelidleaf beetles such as Chaetocnema pulicaria andDiabrotica spp., over a short period of time. Reportsindicate that it is transmitted at very low rates viainfected seed.

When MCMV occurs in combination with maize dwarfmosaic virus (MDMV) or wheat streak mosaic (WSMV), itproduces a severe reaction known as maize lethalnecrosis (MLN; see page 96).

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Maize dwarf mosaic virus (MDMV)

Sugarcane mosaic virus (SCMV)

These viruses are transmitted by several genera andspecies of aphids, including Rhopalosiphum maidis (Fitch)and also by seed at low rates (Photo 89). After feedingon an infected plant, the aphid can immediately transmitthe virus. These pathogens can infect other grass andcereal hosts, such as sorghum, Johnsongrass, andsugarcane. No infection occurs in broad-leaf plants.Infected plants develop a distinct mosaic— irregularitiesin the distribution of normal green color—on theyoungest leaf bases (Photo 90). Sometimes the mosaicappearance is enhanced by narrow chlorotic streaksextending parallel to the veins. Later on, the youngestleaves show a general chlorosis, and streaks are largerand more abundant (Photo 91). As plants approachmaturity, the foliage can turn purple or purple-red.Depending on time of infection, there may be severestunting of the plant. Plants infected early may producenubbins or be totally barren.

In China, SCMV has been reported as seriously affectingmaize production.

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Maize lethal necrosis (MLN)

This disease results from combined infection bytwo viruses: maize chlorotic mottle virus (MCMV)and either maize dwarf mosaic virus (MDMV) orwheat streak mosaic virus (WSMV). No lethalnecrosis will develop if only MDMV and WSMVoccur together. Infected plants are short. Theleaves show chlorosis and die at about floweringtime (Photo 92). There is no ear development inplants infected during early stages of growth.

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Maize mosaic virus I (MMV)

The disease has been found in many countriesworldwide. The vector is the planthopper Peregrinusmaidis, which will transmit the virus for most of itslife after feeding on an infected plant. The vectoralso transmits maize stripe virus. Hosts for MMVinclude maize, sorghum, and a few othergraminaceous species. Plants are most susceptiblewhen infected 4 to 6 weeks after emergence. Themost conspicuous symptoms are dwarfing andstriping along the veins (Photos 93, 94).

Degree of dwarfing depends on plant age atinfection. Because internodes are shortened, leavesappear “crowded” and erect. Fine continuous stripesdevelop along the veins beginning at leaf bases.Later symptoms include shorter-than-normal leaveswith a rough and fleshy appearance. Stripes may bedark yellow, and may finally become necrotic. Priorto total necrosis of the tissues, foliage turns red ordark purple.

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Maize stripe virus (M StV)

This disease has been reported in tropical locations inAfrica, Asia, and the Americas, including Hawaii, India,and Australia.

Initial symptoms on the leaves are small chloroticspecks that later develop into narrow parallel chloroticstripes along the younger leaves. The chlorotic bandscan vary in width and extend from the base to thetip of the leaves (Photos 95, 96). Infected plants usuallyshow stunting and bending of the tassel. Normally eardevelopment and yield are reduced.

The virus is transmitted by the planthopper Peregrinusmaidis, and the vector will transmit the virus for mostof its life after feeding on an infected plant. Thevector can also transmit maize mosaic virus.

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Maize streak virus (MSV)

The disease, reported first from East Africa, has nowextended to many other African countries. The virusis transmitted by Cicadulina spp. leafhoppers.Cicadulina mbila (Naude) is the most prevalentvector, and will transmit the virus for most of its lifeafter feeding on an infected plant. Early diseasesymptoms begin within a week after infection andconsist of very small, round, scattered spots in theyoungest leaves. The number of spots increaseswith plant growth; they enlarge parallel to the leafveins. Soon spots become more profuse at leafbases and are particularly conspicuous in theyoungest leaves. Fully elongated leaves develop achlorosis with broken yellow streaks along theveins, contrasting with the dark green color ofnormal foliage (Photos 97, 98). Severe infectioncauses stunting, and plants can die prematurely orare barren. Many cereal crops and wild grassesserve as reservoirs of the virus and the vectors.

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Maize rough dwarf virus (MRDV)

This virus has been known for several years incountries in Europe and Asia, as has its variant, “Malde Rio Cuarto,” in central Argentina and Uruguay.Infected plants show stunting; secondary veinsbecome chlorotic and thick. The leaves becomeleathery and younger leaves roll upwards withcharacteristic overgrowths (enations) on the veins onthe underside (Photo 99). Symptoms can be detectedin seedlings at approximately one month of age. Inlater stages, infected plants develop a reddish colorand form either no ear or simply nubbins which areoften bent at the tip. The tassels and upper leaves aremalformed and underdeveloped (Photo 100).

The virus is transmitted by several delphacidplanthoppers including Laodelphax striatellus forMRDV and Delphacodes kuscheli for MRCV.Transmission is for most of the life of the vector afterfeeding on an infected plant, and females can passthe virus to the next generation through the eggs.

Mal de Rio Cuarto Virus in central Argentina andMRDV in northern China have been reported asseriously affecting maize production.

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Maize fine stripe virus(Maize rayado fino virus, or MRFV)

“Rayado fino”, or fine stripe, is caused by a virustransmitted by the leafhopper Dalbulus maidis. Thevector will transmit the virus for most of its life afterfeeding on an infected plant. Dalbulus maidis is also avector of the corn stunt spiroplasma and maize bushystunt phytoplasma. This virus is found from southernNorth America to South America, including theCaribbean, and has been observed in several CentralAmerican countries to reduce yields by as much as 43%.

Leafhoppers can vector more than one of thesepathogens at a time, and mixed infections are common.Symptoms develop about 2 weeks after plants havebeen infected. They begin as small, isolated chloroticspots easily observed by holding leaves against the light(Photo 101). Later, the spots become more numerousand fuse, forming 5 to 10 cm stripes that advance alongthe veins (Photo 102). If infected at tasseling, plants maynot show symptoms. Poor grain set and grain filling areobserved with infection at the seedling stage.

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Maize bushy stunt (MBS)Maize Bushy Stunt phytoplasma, syn. Maize Bushy Stuntmycoplasma

This disease has been reported in several countriesfrom the southern USA to Argentina. The pathogen istransmitted by the cicadellid leafhoppers Dalbulusmaidis, D. elimatus, and other species of Dalbulus andwill be transmitted for most of the life of the vector,after it feeds on an infected plant. The same vectors cantransmit MRFV and the corn stunt spiroplasma, wheremixed infections in the plant are common.

The pathogen is a non-helical mollicute known as aphytoplasma, earlier referred to as a mycoplasma. MBSis more common in relatively cooler areas, whereas cornstunt is favored by hot and humid environments.

Infected plants show diverse symptoms, depending onthe maize genotype. The most common symptoms aremarginal chlorosis on young leaves, and tips graduallyturn purple-red as they approach maturity.

A conspicuous symptom is the bushy appearance due toa proliferation of tillers, which also become chlorotic andreddish (Photo 103). It is more common in highlandgermplasm. Foliar symptoms are more obvious close toflowering time. Axillary buds develop into barren shoots.With early infection ears are produced at many nodes,but with reduced ear diameter and grain size, greatlyreducing yield (Photo 104).

Simple observation in the field will not allow one todistinguish between symptoms caused by the maizebushy stunt phytoplasma and those resulting from cornstunt spiroplasma.

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Corn stunt (CS)Spiroplasma kunkelii, syn. Corn Stunt Spiroplasma

The disease is known in hot humid lowlands ofseveral countries of Central and South America, theCaribbean, southern USA, and Mexico, but can alsobe found up to elevations of more than 2000 metersabove sea level. The disease is transmitted by thecicadellid leafhoppers Dalbulus maidis, D. elimatus,and other, less important Dalbulus spp. Vectors cantransmit the pathogen for most of their lives afterfeeding on an infected plant. The same vector cantranmit MRFV and MBS, and mixed infections arecommon. The pathogen is the helical mollicuteSpiroplasma kunkelii.

Infected plants show diverse symptoms, dependingon maize genotype, the most common being leafreddening or purpling, yellowing (Photo 105), andthe presence of chlorotic stripes at the base ofyounger leaves, which might turn purple-red towardthe tip (Photo 106). Foliar symptoms normally appearclose to flowering time. Plants are stunted due to theshortening of internodes; axillary buds develop asbarren shoots or ears at many nodes, and there isexcessive root branching. In severe cases, plants arebarren, or there is a significant reduction in eardiameter or poor seed set. Plants die prematurely.

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Diagnostic key

Symptoms Disease Page

Stalk

Black discoloration of stem; Charcoal rot 57shredding of interior;bundles of black material.

Narrow elongated brown Anthracnose stalk rot 54lesions on the stem turningblack, wilting with dark brownshredded vascular tissue.

Broken stalks; brownish Stenocarpella stalk rot 61pith; later, abundant Gibberella stalk rot 46spore-producing structures. Fusarium stalk rot 46

Brown lesions; rotting. Brown spot 2

Brown vascular bundles Black bundle disease 53extending across the and late wiltinternodes startingin roots; wilting of plantbeginning at flowering.

Chlorotic and reddish leaves; Maize bushy stunt 108stunting; plant may be bushywith many tillers.

Dry plant; stalk interior Botryodiplodia 58shredded and discolored; stalk rotblack, cottony masses.

Stunting; chlorosis; death Maize lethal 96around flowering time. necrosis

Stunting; shortened Maize chlorotic 92internodes; green patches mottle viruson leaves.

Maize chlorotic 91dwarf virus

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Stunting, shortened Corn stunt 111internodes; axillary buddevelopment; excessive rootbranching; leaf reddening and/or marginal yellowing, chloroticstreaks at bases of leaves.

Twisting; dark internodes, soft Pythium stalk rot 45and water soaked; lodging.

Water-soaked, dark areas Bacterial stalk rot 84at base of stalk; unpleasantodor, lodging.

Leaf

Downy growth on upper or Downy mildew 5lower leaf surface, striping,partial leaf symptom orgeneral chlorosis; narrow,abnormally erect leaves.

Lesions, with brown Curvularia leaf spot 33centers, about 2 mm indiameter.

Lesions, beginning as Gray leaf spot 34small, regular, elongatedbrownish graynecrotic spots, andgrowing parallel to the veins.

Lesions, coalescing to Septoria leaf blotch 38produce severe blotchingand necrosis.

Lesions, elongated, Turcicum leaf blight 17spindle-shaped, andnecrotic; may coalesceto “burn” plant.

Symptoms Disease Page

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Lesions, necrotic, Macrospora 42elongated, with narrow leaf stripeyellow margins, alongthe veins.

Lesions, oval, necrotic, Yellow leaf blight 25and parallel to the veins,later blighting the leaf.

Lesions, oval, zonate, Carbonum leaf spot 21and brownish, or brownslender and elongated.

Lesions, pale green along veins Bacterial leaf stripe 88developing to stripes, laterbecoming grayish whiteto brown and shredding.

Lesions, round and Eyespot 41translucent, developingtan centers, black-to-purple rings and yellow halos.

Lesions, small, necrotic Leptosphaeria 29coalescing into leaf spotconcentric necroticspots.

Lesions, small, light brown in Maydis leaf blight 18color, elongatingalong secondary veins,and often coalescing.

Lesions, water-soaked with Stewart’s wilt 87irregular margin spreadingalong veins, often turning yellowand moving to the stem.

Symptoms Disease Page

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Mosaic pattern on Maize dwarf mosaic virus 95youngest leaves; chlorotic Sugarcane mosaic virus 95streaks and generalchlorosis, then purple-red;some stunting.

Pustules, small, round, powdery Polysora rust 10light orange; later, turning black.

Pustules, small, elongate, Common rust 9powdery, dark brown; later,turning black.

Pustules, small, round- Tropical rust 10to-oval, surrounded byblack rim.

Rings, large, concentric, Zonate leaf spot 37necrotic.

Spots, concentric, on Banded leaf and sheath blight 26leaves and sheaths;filamentous masses Borde blanco 13develop on lesions.

Spots, shiny, raised and Tar spot complex 14black; later with necrosiscoalescing and drying foliage.

Spots, chlorotic on leaf lamina Brown spot 2and brown spots on leafmidribs, sheaths, and stems.

Irregular oval to elongate Anthracnose leaf 22lesions with yellow to reddish- blightbrown margins on young andvery old leaves.

Spots, small, light green Septoria leaf blotch 38to yellow, turning brown.

Spots, small and necrotic, Curvularia leaf spot 33with light colored halos.

Symptoms Disease Page

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Spots, small, oval, and water- Turcicum leaf blight 17soaked, enlarging to ellipticalnecrotic lesions.

Spots, small and pale green, Phaeosphaeria leaf spot 29round to slightly elongatelater becoming bleached,then necrotic, with a dark brown margin.

Small, round spots on leaves Hyalothyridium leaf spot 30turning to brown necrotic lesions(3-4 cm) with concentric ringssurrounded by chlorosis.

Necrotic, elongated bicolor Borde blanco 13lesions on the border of the leafwith small white mushroomsformed on the lower surface.

Spots, small and whitish, Maize fine stripe virus 107coalescing into a line.

Streaking, broken and Maize streak virus 103yellow, beginning assmall, white, round spots.

Striping, chlorotic. Maize chlorotic mottle virus 92Maize fine stripe virus 107Maize streak virus 103

Striping, chlorotic; Maize mosaic virus I 99leaves appear crowdedand erect; leaves rough,fleshy, dark purple.

Striping, white to yellow and Corn stunt 111broad, turning purple towardleaf tips, leaf reddening and/ormarginal yellowing.

Symptoms Disease Page

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Wilting, from top leaves, Black bundle disease 53at tasseling stage. and late wilt

Firing of upper leaves Charcoal rot 57beginning at tasseling.

Ear

Barrenness, or poor seed set. Downy mildew 5Corn stunt 111Maize bushy stunt 108Stewart’s wilt 87

Black, shiny kernels; Botryodiplodia 79husks black and shredded. (black kernel rot)

Blue-green powder on cob; Penicillium ear rots 63streaked and bleached kernels.

Brown-green streaks on Hormodendrum 80kernels, starting at cob base. ear rot

Cottony, white-to-pink Gibberella ear rot 67growth; some germination Fusarium moniliforme ear rot 67on the cob. Cephalosporium kernel rot 80

White streaks on the pericarp. Fusarium moniliforme ear rot 67Cephalosporium kernel rot 80

Lesions, oval, and larger Maydis leaf 18than 2.3 cm on husks and blight “T” strainleaf sheaths.

Lightweight, chaffy ears; Nigrospora ear rot 72loose, discolored kernels; Charcoal ear rot 71black specks on kernelsand cob.

Lightweight ears; loose kernels; Tar spot complex 14germination of seed on cob.

Symptoms Disease Page

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Nubbins, or ears with Black bundle disease 53underdeveloped, shrunkenkernels.

Nubbins or no ears at all. Maize dwarf mosaic virus 95Sugarcane mosaic virus 95Downy mildews 5Stewart’s wilt 87Maize rough dwarf virus 104

Pink/ red kernels, starting at Gibberella ear rot 67ear tip.

Scattered kernels on the ear Fusarium moniliforme ear rot 67with pink fungal growth.

Rotten and blackened ears. Carbonum ear rot 21

Rotten ears; light brown Banded leaf and 26cottony fungal growth ; sheath blightfilamentous masses on kernelsand cob producing small,round, black sclerotia onhusk leaves.

Slimy, soft, pale, masses Ergot 68replacing kernels; hardeningtoward harvest.

Spore masses, black and Head smut 49loose, instead of ear.

Damaged kernels with Aspergillus ear rots 64black, yellow-green, ivygreen or whitish, powderyspore masses.

Starts as fine stripes going Maize stripe virus 100often to broad bands of chlorosis.Often the top of the plant bends.Underdevelopment of ear.

Symptoms Disease Page

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White galls, closed replacing Common smut 76kernels; later, black spore masses.

White-gray fungal growth Gray ear rot 75between kernels; husks bleachedand adhering to each other,later turning black with sclerotia.

White fungal growth; gray- Stenocarpella ear rot 83brown ear; black pycnidia ;husks adhering to ear.

Yellow, loose kernels; Charcoal ear rot 71black filamentous masses.

Tassel

Malformation and enlarge- Head smut 49ment; black spores in florets.

Malformation and Downy mildews 5enlargement; sterility.

Malformation and frequently Maize chlorotic mottle virus 92reduced or aborted. Maize rough dwarf virus 104

Maize bushy stunt 108

Rotten tassel, enclosed in Bacterial leaf stripe 88dead leaves.

Spore masses, hard and dark False head smut 50green to black on a few florets.

White galls closed on the Common smut 76tassel, later black spore masses.

Male sterility; some male Corn stunt 111florets in tip of ear. Maize bushy stunt 108

Stunting and bending. Maize stripe virus 100

Symptoms Disease Page