Maize remains a cornerstone of food security and livestock feed systems across Africa, yet its productivity is continually threatened by a range of destructive leaf diseases.
According to a recent publication in SA Graan/Grain by Dr Belinda Janse van Rensburg of the ARC-Grain Crops institute in Potchefstroom, understanding the economic impact, distribution, symptoms, and control of major maize diseases is essential for producers aiming to safeguard yields and profitability.
The article, titled “The big five maize leaf diseases: identification and management” (SA Graan/Grain, March 2026), highlights five critical diseases—each with distinct characteristics but collectively capable of causing severe crop losses if not properly managed.
Economic importance of maize leaf diseases
Leaf diseases significantly reduce photosynthesis, impair plant growth, and ultimately lower grain yield and quality. In severe cases, losses can range from 30% to as high as 100%, depending on the disease and timing of infection.
For instance, northern corn leaf blight and grey leaf spot alone can reduce yields by up to 50% under favourable conditions, while maize streak virus can wipe out entire crops in extreme infections.
Such losses have far-reaching implications—not only for farm profitability but also for national food security, particularly in maize-dependent regions.
The “big five” maize leaf diseases
1. Northern corn leaf blight (NCLB)
Caused by the fungus Exserohilum turcicum, NCLB is prevalent in cooler, high-rainfall areas. It spreads through wind and rain splash, surviving on crop residues.
Symptoms:
- Long, cigar-shaped grey-green lesions
- Progression from lower to upper leaves
- Premature leaf death in severe cases
Impact:
Yield losses of up to 30–50%, especially when infection occurs early.
Control:
- Plant resistant hybrids
- Rotate with non-host crops such as legumes
- Manage crop residues through tillage
- Apply fungicides early when necessary
2. Grey leaf spot (GLS)
This globally important disease, caused by Cercospora zeae-maydis, thrives in warm, humid conditions and is common in high-rainfall and irrigated regions.
Symptoms:
- Rectangular grey lesions between leaf veins
- Lesions coalesce, leading to leaf blight
Impact:
Yield reductions of up to 50% in susceptible hybrids.
Control:
- Use resistant varieties
- Practice crop rotation for one to two years
- Manage residues and consider cover crops
- Apply fungicides at key growth stages under high pressure
3. Bacterial leaf streak (BLS)
Caused by Xanthomonas campestris pv. zeae, BLS spreads through water, rain splash, and contaminated equipment.
Symptoms:
- Narrow, water-soaked streaks between veins
- Streaks turn brown over time
Impact:
Reduces leaf area available for photosynthesis, lowering yield potential.
Control:
- Field hygiene and sanitation
- Crop rotation
- Residue management
- Balanced fertilisation and weed control
Notably, fungicides are ineffective against this bacterial disease, making accurate diagnosis critical.
4. Goss’s wilt
A bacterial disease caused by Clavibacter michiganensis subsp. nebraskensis, recently identified in South Africa, Goss’s wilt poses an emerging threat.
Symptoms:
- Dark green to black streaks with water-soaked margins
- Shiny exudates on leaves
- Leaf blight and systemic wilting
Impact:
Severe yield losses, especially under plant stress conditions.
Control:
- Plant resistant hybrids
- Avoid movement of infected residues
- Practice crop rotation
- Control weeds that may act as alternate hosts
Since it is bacterial, chemical control options are limited.
5. Maize streak virus (MSV)
One of the most economically significant viral diseases in Africa, MSV is transmitted by leafhopper insects (Cicadulina spp.).
Symptoms:
- Chlorotic streaks on leaves
- Stunted growth
- Poor ear development
Impact:
Yield losses can reach 100% in severe infections.
Control:
- Use resistant or tolerant varieties
- Control insect vectors
- Eliminate volunteer maize plants
While insecticides can reduce vector populations, they are often costly and environmentally challenging.
Integrated disease management: the way forward
A key message from the SA Graan/Grain publication is that no single control measure is sufficient. Instead, integrated disease management is essential.
This includes:
- Regular scouting and early detection
- Accurate disease diagnosis
- Use of resistant hybrids
- Crop rotation and residue management
- Good field hygiene practices
- Judicious use of fungicides for fungal diseases
Importantly, bacterial and viral diseases cannot be effectively controlled with fungicides, underscoring the need for correct identification before taking action.
In an era of increasing climate variability and evolving pathogen threats, proactive disease management is no longer optional—it is essential.
As highlighted by Dr Belinda, by combining knowledge with practical strategies, maize producers can minimise losses, protect crop health, and ensure sustainable production for the future.
