Training on Maize Diseases

1. Identification and management of major diseases of maize
International Training Workshop on Maize Seed Production and Distribution in
Bhutan
November 13 - 15, 2023 | ARDC-Wengkhar, Mongar, Bhutan
Dr. Suresh, L.M.
Maize Pathologist, CIMMYT.

2. N P K

3. Turcicum Leaf Blight:
• Fungal foliar disease
• Affects maize and causes a
crop loss:
• Requires a humidity of 75-
90% RH and temperature of
17-270 C.
• Spreads through crop
debris, arial spread.
Maize disease in Bhutan
Grey Leaf Spot
Fungal foliar disease
Affects maize and causes a
crop loss:
Requires a humidity of 65% RH
for survival and 90% for spread
and temperature of 22 -270 C.
Spreads through crop debris,
arial spread.
Ear rot
Fungal ear rot disease
Affects maize and causes a
significant crop loss:
Requires a humidity of 75-90%
RH and temperature of 20-270 C.
Spreads through crop debris, soil
, insect vectors and arial spread.

4. Northern Leaf Blight (Setosphaeria turcica Syn. Exserohilum turcicum)
Distribution: The disease is occurring worldwide.
Plant species affected (Host range): Maize, Sorghum, and other wild grasses.
Symptoms:
– Early symptoms are pale gray-green, elliptical, or cigar-shaped lesions that are initially less than 1 cm long.
– The disease usually begins as a few scattered lesions in lower leaves and progresses towards upper leaves.
– The disease can develop very rapidly after anthesis resulting in complete blighting of the leaves. Large oval
gray elongated light brown spots. Symptoms often occur on lower leaves.
Conditions for disease development:
– E. turcicum overwinters as mycelia and conidia in and on leaf debris.
– Conidia can be carried by wind over a long distance.
– Secondary spread within and between fields occurs by conidia produced abundantly in leaf lesions on
susceptible plants.
– Symptoms often progress from lower leaves to upper leaves as conidia produced in lesions on lower leaves
serve as inocula for the infection of the upper leaves.
– Northern corn leaf blight is found sporadically in most humid areas of the world where corn is grown but is
most damaging when moderate temperatures (18-270 C) and prolonged periods of dew prevail during the
growing season.
Impact:
– Cause significant grain yield loss in the hot and humid medium to highland altitudes. If the disease is
established before silking, losses in grain yield of up to 50% may occur. If the infection is moderate or
delayed until 6 weeks after silking, yield losses are minimal.
Management:
a. Plant-resistant and certified seed
b. Practice crop rotation with legumes
c. Collect and decompose previous crop residue in one spot.
d. Whenever is necessary, spray recommended fungicides at the early disease stage.

5. Disease progression of Turcicum leaf blight
(TLB)
Initial infection Long elliptical lesions Blight symptoms near ear position Blight symptoms near flag leaf Complete blight

6. Disease progression of Turcicum leaf
blight (TLB)
Cigar shaped lesions
Blight Symptoms
Coalesce of lesions
Initial symptoms

7. Grey Leaf Spot (Cercospora zea maydis)
Distribution: The disease occurs in temperate, to warm, humid areas of various parts world.
Plants species affected (Hosts): Maize
Symptoms:
• Early lesions are small, necrotic spots with a chlorotic halo that gradually hallo that gradually expands to
full-sized lesions, which can blight entire leaves.
• Expanding lesions are tan and turn grey as the pathogen, Cercospora zeae-maydis or C. zeina, begins to
sporulate on the underside of the leaf. In some cases, lesions have a dark border or yellow halo.
• The diagnostic feature of grey leaf spot lesion is the sharp edges of the lesions results from the inability of
the fungus to penetrate sclerenchyma tissue in the major veins of the leaf, which limits the lateral expansion
of the lesions.
• The opacity of the lesion is caused by stromatic tissue, i.e., dark hardened mycelium produced by the
fungus, in the stomatal cavities. Rectangular elongated, parallel lesions.
Conditions for disease development:
• Severe grey leaf spots are usually found in the field where corn follows corn and residues of the previous
crops remain in the soil surface.
• Germinated conidia of C. zeae-maydis can survive at 60% relative humidity on the leaf surface but require a
relative humidity of 95% or higher for germ tube growth and appressorium formation.
Impact:
Although the disease is not a problem until sometime after anthesis, it can develop rapidly, completely
blighting leaves and causing premature death of the plants. Prolonged periods of dew, fog, and cloudy weather
are conducive to severe grey-leaf spot epidemics. Reduce grain yields due to loss of photosynthetic leaf area.
Management:
• Plant resistant and tolerant genotypes
• Practice crop rotation with legumes
• Collect and decompose previous crop residue in one spot.
Disease cycle of GLS. Source: Ward et al. (1999).

8. Disease symptom progression – Grey leaf spot
Blighting of leaves
Coalescing lesions
Rectangular parallel lesions
Grey Mature lesions
Expanding immature lesions
Initial lesions

9. Ear rot Disease
Fusarium Ear rot
Fusarium verticilloides
• Common in all maize growing ecologies
• Hot dry weather after flowering favors
Fusarium ear rot
• Symptoms
• Whitish/pink mycelium on/between
kernels
• Starburst symptoms on kernels
• Fungi overwinters in crop debris and
airborne conidia infect silks at flowering
• Control through host resistance and proper
storage
• Quantitative Resistance (composition of
kernel is important)
• Prevalent when wet weather follows silking
• White / grey mycelial growth over husks and
kernels
• Infected kernels may be very light and appear
to be glued together
• Black pycnidia are produced late in the
season
• Fungi overwinters in infected stalks
• Most serious under high temp and drought
• Production of aflatoxins
• Overwinters in crop debris and spores are
dispersed by wind or insects
• Host resistance offers best control. Rotation has
minimal effect as a lot of alternate hosts
• Difficult to phenotype. R is likely to be quantitative
but difficult to phenotype reliably
Diploidia ear rot
Stenocarpella maydis
Aspergillus ear rot
Aspergillus flavus
Source: Iowa State University Source: University of Illinois

10. Ear Rots
• Significant yield damage
• Mycotoxin risk
• Highly environmentally variable
• Major Ear Rots
1. Aspergillus ear rot (Aspergillus
flavus)
2. Fusarium Ear Rot (Fusarium
moniliforme and other species
(Gibberella))
3. Diplodia Ear Rot (Stenocarpella
maydis)

11. Thank you
for your
interest!