3. Gray leaf spot (GLS) of maize is caused by the fungus Cercospora
zeae-maydis.
The disease is now recognised as one of the most significant yield-
limiting diseases of maize worldwide.
Not only is it a threat to maize production in the commercial farming sector, it
also reduces yields of maize on small-scale farms.
2
INTRODUCTION
4. Symptoms of leaf spot
4
Early Lesions:
Early lesions of gray leaf spot are small, necrotic spots
and may have a chlorotic halo (more visible when leaf is
backlit).
Lesions usually appear first on lower leaves before
silking.
Lesions progress from lower to upper leaves.
Fully Developed Lesions:
Typical lesions of gray leaf spot are rectangular with
straight edges.
Lesion expansion is limited by parallel leaf veins.
Lesion appearance may differ somewhat on different
genetic backgrounds
This symptom is usually diagnostic.
5. Gray Leaf Spot Occurrence
5
Fungal disease caused by Cercospora zeae-maydis pathogen.
Primary leaf disease of corn in the US,Asia .
Disease of high residue farming - pathogen builds up in corn residue over
time.
Favored by warm temperatures and high humidity.
Extended periods of leaf wetness (~13 hours) allow infection of leaves.
Disease often spreads rapidly with favorable weather during late summer and
early fall (during the grain fill period of corn development).
7. Gray Leaf Spot Impact on Crop
7
Depends on leaf area loss relative to grain fill:
If grain fill outpaces disease progression, yield loss may be minor.
If significant leaf area is lost before grain fill is complete, yield loss will be
greater.
Stalk rots may increase:
Loss of functional leaf area during grain fill may lead to stalk rots as
carbohydrates are taken from stalk to fill kernels.
Stalk lodging may increase harvest losses or slow harvest progress.
8. Management of Gray Leaf Spot
8
GLS-resistant hybrids:
Hybrids with genetic resistance can reduce yield loss due to GLS.
Hybrids and parent lines are rated and screened in "disease nurseries" as well
as locations with high levels of natural GLS occurrence’
Disease resistance scores are provided to customers for all renown® brand
corn products to help them select appropriate products for their fields.
Susceptible hybrids are more likely to benefit from a foliar fungicide application.
9. Cont,d
9
has longer
Crop rotation:
May reduce disease pressure, but rotation is only a partial solution.
Compared to other residue-borne pathogens, gray leaf spot
survival time in debris.
Tillage:
Encourages breakdown of crop residue.
Fungicide application:
Foliar fungicide treatment is the only management option available following
planting.
