Farming often comes with unexpected losses, and post-harvest challenges are common, especially for root and tuber crops such as potatoes, onions, and amadumbe.
For farmers supplying formal markets, this can be serious because produce is expected to be of consistent quality and timing, and any failure to deliver affects income and trust.
Problems such as rotting, holes, maggots, or water damage often appear even when normal practices are followed, making it hard to trace the cause. Understanding these risks can help farmers better prepare for future harvests.
Below-ground crops: Reducing losses
Farm practices that help reduce crop losses begin with understanding soil health, says North West agronomist Mandisa Mazibuko.
She explains that successful crop production depends on knowing what the soil contains, what it lacks, and what each crop needs to grow effectively.
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“This is where extension officer support can play a huge role, by assisting farmers with soil testing and sharing knowledge on fertiliser application and nutrient management,” she says.
Mazibuko notes that vegetable crops such as carrots and beetroot perform poorly in compacted soils with poor drainage. She adds that over-fertilisation should also be avoided, as it can increase soil salinity, damaging roots and resulting in small or poor-quality harvests.
On cultivar selection, she stresses that not all varieties perform equally under different conditions.
“There are beetroot cultivars that can tolerate heat and perform well in specific soil types.”
Mazibuko recommends using disease-resistant cultivars and ensuring farmers are informed about variety selection to reduce losses.
Crop rotation, she adds, remains important in breaking the cycle of soil-borne diseases such as root rot. She also emphasises field sanitation, including the removal of infected plant material and proper weed control, as weeds can harbour pests and increase disease pressure.
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Pests and climate stress challenges
According to Nangamso Mtamzeli-Cekiso, a horticultural scientist at the Dohne Agricultural Development Institute in Stutterheim, Eastern Cape, root and tuber crops such as potatoes, carrots, sweet potatoes, onions, garlic, ginger and turmeric store food in their underground structures and play a vital role in food security and nutrition, particularly in developing regions such as South Africa.
She says these crops are rich in key nutrients like vitamin A, zinc and iron and have a longer shelf life than many above-ground vegetables, making them important for both subsistence and commercial farming systems. However, she adds that production is increasingly threatened by a combination of biological, environmental and soil-related factors.
Mtamzeli-Cekiso explains that below-ground crops are highly vulnerable to pests such as sweet potato weevils and tuber moths, particularly under humid conditions. Climate change is worsening the situation by creating favourable environments for pest outbreaks.
A major cause of losses is the use of infected planting material. In sweet potato production, farmers often reuse vines, which leads to the build-up of viral diseases over time.
“The continuous recycling of planting material leads to the accumulation of viral diseases, resulting in reduced yield and poor crop performance.”
Nangamso Mtamzeli-Cekiso
Mtamzeli-Cekiso says climate variability further contributes to production losses. Excessive rainfall leads to waterlogging and oxygen loss in soils, while drought reduces growth and delays tuber formation. High temperatures reduce yield and quality, sometimes by up to 30%.
She also notes that onion and garlic production is sensitive to light and temperature, where incorrect conditions can prevent proper bulb formation. Low temperatures may cause chilling injury, while in onions, temperatures below 13°C can trigger bolting.
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Soil testing and integrated solutions
Mtamzeli-Cekiso further notes that soil conditions remain central to successful production.
Loose, well-drained sandy loam soils support proper root development, while compacted soils lead to deformities such as forking in carrots and misshapen onion bulbs.
Poor drainage increases the risk of waterlogging and root rot, while excess moisture can cause cracking in carrots.
She tells Food For Mzansi that soil fertility management through soil testing is essential before planting to guide fertiliser use and prevent imbalances such as excess nitrogen or soil acidity.
According to Mtamzeli-Cekiso, crop rotation, use of resistant varieties and field sanitation are key to managing soil-borne pests and diseases. An integrated approach combining improved planting material, climate-smart practices and proper soil management is essential to reduce losses.
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