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The disease symptoms become particularly visible around flowering
– although they can be visible earlier under high disease pressure con-
ditions. This is a leaf disease that occurs specifically in KwaZulu-Natal
and the eastern Highveld, where fog and/or high humidity and high
temperatures prevail.
A misperception exists that the spores of the fungus are only
airborne and distributed by the wind and the rain. Spores can indeed
be spread by the wind, but these are secondary spores that can be
spread from one planting to the next later in the season – and usually
over shorter distances.
The real source of the disease is plant residues from the previous
season in which the fungus survives, and as soon as the conditions
become favourable in the new season, spores are released that can
affect the lower leaves of plants.
These lesions produce new spores that, as the growing season progress-
es, are released and distributed by rain droplets and wind to newer leaves
higher up on the plant. Grey leaf spot is often confused with sunburn/
drought inhibition (
Photo 4
). Needless to say, the drought damage cannot
be controlled and the unnecessary administration of fungicide causes a
double setback for the farmer. None of the fungal leaf diseases mentioned
is seed-borne.
BACTERIAL LEAF STREAK
Bacterial leaf streak (
Photo 5
) is a disease that specifically occurs in
the western production areas and these symptoms are confused with
those of grey leaf spot. A bacterial disease cannot be controlled with
fungicides and spraying for it can be an expensive mistake – without
any result.
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Leaf disease/
symptom
Type
Growth stages
Conditions
Fungicide
Control
Common rust
(Photo 2)
Fungus
Later V stages (V8+) Moderate temperatures
(16°C - 25°C).
Yes
Fungicides and hybrid selection.
Northern corn
leaf blight
(Photo 1)
Fungus
V6 to R stages
Moderate temperatures
(18°C - 27°C); long dew periods/
high humidity.
Yes
Fungicides, hybrid selection, crop
rotation and ploughing in of plant
residues.
Grey leaf spot
(Photo 3)
Fungus
Fungus From flower-
ing (VT - R1+)
Moderate to hot temperatures
(22°C - 30°C); long dew periods/
high humidity (>95%).
Yes
Fungicides, hybrid selection, crop
rotation and ploughing in of plant
residues.
Maize streak
disease
(Photo 6)
Virus
V stages
Tropical areas here hosts are
present all year, as well as
conditions that increase vector
activity (particularly hot
irrigation areas).
No
Control leaf hoppers (systemic
seed treatments and sprayings)
and weed control.
Bacterial streak
(Photo 5)
Bacterium From flowering
(VT - R1+)
Warm, irrigation areas.
No
Crop rotation, fallow fields and
destroy infested plant residues.
Sunburn
(Photo 4)
Environment All stages
Heat/sun inhibition.
No
Hybrid selection and moisture
management.
Phaeosphaeria
leaf spot
Fungus and
possible
bacterium
complex
R3+
Areas with high umidity and
cool night temperatures.
Less effective Not usually necessary, but hybrid
selection destroys infested plant
residues and moving of planting
date can help.
Downy mildew Fungus
Early V stages
Warm, moist areas (tropical
areas), particularly in fields
where the disease was observed
before. Soil temperatures above
20°C promote infection.
Yes
Soil treatments with metalaxyl,
earlier planting date in infested
fields, good quality seed and
avoid crop rotation with sorghum.
Diplodia leaf
streak
Fungus
All stages
Warm, moist areas and
minimum tillage.
Yes
Crop rotation, good agl practices
and ploughing in of plant residues.
Eyespot
Fungus
R3+
Cool, moist conditions,
minimum tillage, insect pests
like thrips and aphids an
promote infestation.
Yes
Crop rotation, ploughing in of
plant residues and insect control.
Polysora rust
Fungus
R3+
Tropical areas, warm
(24°C - 28°C), humid weather.
Yes
Fungicides and earlier.
More general leaf diseases on maize in South Africa, the disease-causing organisms and
growth stages in which they are commonly observed, and the control strategies for them.
MADE POSSIBLE BY
THE MAIZE TRUST
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