The Agricultural Research Council (ARC), supported by funding from the Department of Agriculture, has launched an initiative to evaluate the impact of climate change on vegetable production in the Northern Cape. The goal of this initiative is to develop practical recommendations for farmers, especially those in arid regions. This includes suggestions for suitable alternative production locations.

By Johleen Malaka, Graig Sithole and Nadia Araya from ARC-Natural Resources and Engineering

The Northern Cape is one of the driest provinces in South Africa, with an average annual rainfall of less than 200 mm in many areas. Despite the harsh conditions, vegetable farming is crucial for ensuring regional food security and supporting the livelihoods of smallholder farmers. However, climate change is introducing more unpredictable weather patterns, such as intense heatwaves, erratic rainfall, and prolonged droughts, making it increasingly difficult to grow crops in these environments.

In October 2024, the ARC, with funding from the Department of Agriculture, launched an important initiative to assess the impact of climate change on vegetable production. The goal is to develop practical recommendations for farmers, particularly those in arid areas, including suggestions for suitable alternative production locations.

Our research and development efforts were conducted on a smallholder vegetable farm in the ZF Mgcawu District Municipality, Northern Cape Province. The trial involved eight high-value vegetable crops – beetroot, carrot, lettuce, onion, spinach, cucumber, tomato, and pepper – selected for their nutritional content, market value, and potential adaptability to warm, arid climates. Despite the challenges of conducting fieldwork in these harsh conditions, we encountered several obstacles that provided valuable learning opportunities, particularly in the areas of pest management and plant spacing.

Arc Northern Cape Crops 2_Supplied — Damage caused by African bollworm (Helicoverpa armigera) larvae on tomato fruits at Groenvingers Vegetable Farm in the Northern Cape Province. Photo: Supplied

Arc Northern Cape Crops 3_Supplied — African bollworm (Helicoverpa armigera).

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African Bollworm infestation across multiple fruity vegetable crops

A significant challenge during the trial was the unexpected outbreak of African bollworm (Helicoverpa armigera), which affected not only our cucumber crops but also tomatoes and chili peppers. Although this pest typically targets crops like maize and cotton, it has a wide host range and can adapt to new environments and crop types, particularly under changing climatic conditions. The larvae generally damage the fruit, while the adult stage targets the leaves.

In our experiment, we observed that the larvae bored into developing fruits, causing internal rotting and visible holes that rendered the produce unmarketable. In several instances, a single larva damaged multiple fruits, drastically reducing the overall yield and market quality of the crop. The outbreak was likely exacerbated by high temperatures following an excessive period of rainfall. These environmental factors are known to accelerate the bollworm’s life cycle and increase its reproductive rate. This situation highlighted the importance of routine pest scouting, not just for common pests but also for opportunistic ones that may emerge due to ecological shifts. Under changing climate conditions, pests can shift hosts or expand their range, making integrated pest management (IPM) even more crucial.

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Plant Spacing Issues: Overcrowding from Over-Seeding or Transplanting

To improve the chances of seedling establishment in warm, dry climatic conditions, we chose to plant multiple seeds or seedlings per hole for crops such as carrot, spinach, beetroot, and spring onion. This approach was intended as a hedge against poor germination rates, often caused by high soil surface temperatures and rapid moisture loss. However, while this strategy improved initial emergence rates, it inadvertently led to severe overcrowding, with multiple seedlings competing for space, water, light, and nutrients. This experience emphasised that over-seeding can be counterproductive, especially if thinning is not done promptly.

Arc Northern Cape Crops 4_Supplied — The consequences of over-seeding or -transplanting were visible across different study crops, including (a) carrots which became stunted and developed forked or twisted roots, (b) spinach which produced small, pale, fragile and crowded leaves, (c) beetroot which produced small roots and (d) spring onion which showed slow growth and low yield. Photo: Supplied

Thinning, an often-overlooked practice, is labour-intensive and time-sensitive, particularly on small farms with limited manpower. Nevertheless, it remains one of the most cost-effective agronomic practices for ensuring uniform crop stands. Thinning should ideally be done when seedlings are 5-10 cm tall, and the removed plants can even be transplanted to fill gaps where there are missing plants, thereby minimising waste. This experiment demonstrated that proper spacing is critical for healthy crop development and optimal yields, particularly for root and leafy crops.

Transplanting multiple seedlings of spring onion in one hole resulted in slow growth and development, leading to reduced yields. The tightly clustered seedlings had limited space between them, competing for light, nutrients, and root space, which restricted the energy available for bulb enlargement. Furthermore, excessive leaf density shaded the lower leaves, causing yellowing and reduced photosynthetic efficiency.

Arc Northern Cape Crops 6 — Transplanting multiple seedlings of spring onion in one hole resulted in slow plant growth and development, with consequent yield reduction. Photo: Supplied

Also read: Smarter pest management essential for potato sustainability

Key Takeaway Messages

Scout Regularly and Widely:

Don’t assume a pest only affects specific crops. Pests like the African bollworm can adapt to new hosts under changing climatic conditions.
Inspect crops regularly from the seedling stage to fruiting to detect signs of infestation early (e.g., holes in leaves or fruit, frass, or larvae).
Introduce biological controls as part of an integrated pest management (IPM) approach.

Avoid Over-Seeding:

Planting too many seeds per hole may seem like a way to increase germination chances in warm conditions, but it leads to overcrowding.
Overcrowded crops, such as carrots, spinach, spring onions, and beetroot, suffer from stunted growth, poor root or bulb development, and reduced yield quality.
Invest in high-quality seeds and consider pre-soaking or priming them before planting to enhance germination, which can reduce the need for over-seeding.

Don’t Skip Timely Thinning:

Thinning enables each plant to develop to its full potential, improving uniformity, bulb size, and overall market value.

Despite these challenges, the trial provided practical, real-world lessons that will guide our future recommendations for vegetable production in arid regions. With climate change creating new pressures on agriculture, adaptability, research, and knowledge-sharing among farmers are more important than ever.

Acknowledgements: Special thanks to the Department of Agriculture for funding and to the Agricultural Research Council (ARC) for implementing the project.

Inquiries: Dr Nadia Ibraimo Araya IbraimoN@arc.agric.za