Grain SA study urges farmers to understand maize diseases as losses spike
Research shows poor disease management can cut maize harvests by as much as 30% to 100%.
SOUTH AFRICA – A recent article in Grain SA’s SA Graan/Grain publication, by Dr Belinda Janse van Rensburg from the ARC-Grain Crops institute stresses that farmers must understand these diseases to protect both yield and income.
The report explains that infections can reduce harvests by between 30% and 100% depending on severity and timing.
“Understanding the economic impact, symptoms, and control of these diseases is essential for producers,” Dr Belinda said.
The study identifies northern corn leaf blight, grey leaf spot, bacterial leaf streak, Goss’s wilt, and maize streak virus as the most serious threats. Each disease affects plant health in a different way, but all reduce photosynthesis and weaken growth.
Northern corn leaf blight and grey leaf spot can cut yields by up to 50% under the right conditions. Maize streak virus remains the most severe, with the ability to destroy entire fields in extreme cases.
“In severe infections, maize streak virus can wipe out whole crops,” the report notes.
These losses go beyond individual farms. Many African countries depend on maize as a staple food, meaning reduced output can affect both food prices and supply.
The report makes it clear that farmers cannot rely on one method to manage these diseases. Instead, it calls for a mix of approaches such as planting resistant seeds, rotating crops, managing residues, and keeping fields clean.
Fungicides can help control fungal diseases, but they do not work on bacterial or viral infections. This makes correct diagnosis important before farmers take action.
“No single control measure is sufficient. Farmers must combine several strategies to reduce risk,” Dr Belinda explained.
Lower harvest adds urgency
The findings come as South Africa expects a slightly smaller maize harvest in the 2025/26 season. The Crop Estimates Committee projects output at 16.13 million metric tons, about 3% lower than the previous season’s 16.65 million tons.
Despite the drop, the country still produces more than its annual demand of about 12 million tons. This means South Africa can continue to supply both local and export markets.
Recent export data shows strong regional demand, with shipments expected to reach about 2.4 million tons by the end of the current season.
With disease risks and changing weather patterns affecting production, experts say farmers must act early to protect crops and maintain stable supply.
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