Estimated reading time: 6 minutes
The theme of the first webinar in CropLife SA’s popular training series for 2025-2026, was “Re-evaluating planting windows in a changing environment for crop resilience”, presented by Dr Nicky Creux, senior lecturer at the University of Pretoria’s (UP) Department of Plant and Soil Sciences in the Forestry and Agricultural Biotechnology Institute (FABI). The webinar explored how shifting climates affect planting dates, the risks linked to late planting, and factors contributing to these risks.
Dr Creux introduced FABI as a postgraduate institute that connects industry, academia, and government to tackle major challenges in agriculture and forestry. Spanning two faculties which include natural and agricultural sciences as well as engineering, built, environment, and IT, FABI’s multidisciplinary team includes experts from departments such as plant and soil sciences, biochemistry, genetics and microbiology, entomology, and computer science, enabling a collaborative approach to agricultural research.
FABI’s role
Dr Creux highlighted FABI’s role at the UP in applying foundational research to practical challenges in agriculture and forestry. Offering non-profit services, FABI combines research, training, and services to build sector expertise. She also contributes to the Grain Research Programme (GRP) and FABI’s Diagnostics Clinic, which analyses samples and supports nationwide pest surveillance.
Data is fed into a cloud-based platform managed by Prof Bernard Slippers for real-time pest mapping. Dr Creux also leads the FABI’s Crop, Floral Biology, and Environment (CFBE) team, which studies how sunflower and maize respond to environmental change, collaborating with the Agricultural Research Council (ARC) and Ghent University on phenotyping and imaging to support resilient crop development.
Climate modelling
Dr Creux said historical climate assessments confirmed that significant changes have occurred in major agricultural districts over the past 30 years. These findings suggest that provincial-level policies or general estimates are not sufficient for on-farm applications and that climate impacts must also be assessed at the district level. She added that provincial level estimates might be useful for making provincial-level decisions and planning, but will not give the full information to farmers who are working at district level.
“I think it highlights the importance of continuously re-evaluating planting dates as climate change progresses.” She said there must be a clear understanding how climate change affects agriculture in Southern Africa, where warming is expected to occur at twice the global rate. Studies show declining land suitability for maize under future climate scenarios. High seasonal variability in South Africa can mask steady temperature increases, making trends harder to observe on the farm level.
She said research using 30 years of district-level weather data confirmed regional warming is already occurring, but despite this, overall maize yields have risen – boosted by GM (Genetically Modified) crops and mechanisation over the same period. Far-future climate modelling of maize production regions showed longer, hotter summers and shifting frost dates, underscoring the need to re-assess planting windows as conditions change to sustain crop performance. She said it is important to note that these projections apply to many years in the future.
“As climate change progresses, it is really going to be important for us to monitor planting windows and make sure that we are still aligning growth and development of plants with the appropriate climatic conditions because these may well shift as the summers get longer and hotter.“
Contributing factors to decreasing yields at later planting dates
Research done by her team and other stake holders focussed on the factors contributing to poor yields when planting occurs later in the season, particularly temperature fluctuations and water availability. These two variables significantly influence plant growth dynamics and can severely limit development if not aligned with critical growth stages.
Temperature and water availability are key factors behind lower yields at later planting dates. To understand how the change in heat units and water availability are affecting the plant’s development and growth, Dr Creux and Dr Dirk Swanevelder at the ARC teamed up to plant maize and sunflower at different planting dates under his state-of-the-art high-throughput phenotyping system – the first of its kind in Africa when it was first built.
Using RGB (red, green and blue), near-infrared, and LiDAR imaging, the phenotyping system scans plants three times daily to create 3D plant models and measure traits like height, leaf angle, and biomass. Figures 1 and 2 below show clear differences emerged between maize planted in November-December versus January-February. Plants in the later plantings (January and February) grew faster early on, leading to earlier maturity, less biomass, and reduced yields. In contrast, earlier plantings grew steadily and bulked out more effectively.
Dr Creux explained that the phenotyping system is high-resolution and can actually see differences across cultivars. The graph below shows research that was conducted and concluded that over the January planting date everything seems to respond almost the same, while differences in cultivars were noted over the November planting date as some cultivars were growing much faster and some slower. “This will allow us to look at cultivars that maybe respond better to different planting dates over time.”
She also explained that research conducted showed that water stress also increased, with later planting dates showing reduced transpiration, photosynthesis, and seed weight.
Pollination influence
Dr Creux said some research conducted by her team members showed that maize flowers become less receptive to pollen at later planting dates, while sunflowers appear to be better at withstanding heat stress before and during flowering, helping them maintain yield. She explained that research shows heat stress affects pollination timing and flower development. Sunflowers adjust pollen release to match insect visits, maintaining yield. In maize, silk receptivity varies by planting date, impacting pollination success. These findings highlight pollination as an additional factor in yield loss under late planting and climate stress.
Diseases
Additionally, both maize and sunflower crops showed increased disease incidence when planted late in the season. “This is important because it’s not just about temperature and water,” Dr Creux explained. “There’s little we can do to control temperature and we can’t change heat accumulation. Water availability can be improved through irrigation, but even that has its limits.” She emphasized the potential of selecting or developing cultivars with altered pollination mechanisms that are more resilient under late planting conditions. “If we better understand the impact of disease at later planting dates, we could refine our disease-control strategies to mitigate some of the yield losses we’re seeing,” she added.
Surveys showed sunflower and maize planted later in the season face higher disease pressure, including increased Alternaria and Sclerotinia head rot. Bidens mottle virus was also identified in South African sunflowers for the first time. Stress and favourable conditions for pathogens likely reduce crop resistance, increasing disease severity and lowering yields.
Dr Creux highlighted the importance of closely monitoring planting dates as climatic conditions continue to evolve, urging stakeholders to adapt strategies based on localised, district-level data. – Christal-Lize Muller, Plaas Media
For more information contact Dr Nicky Creux at nicole.creux@fabi.up.ac.za.
Links to published open access works:
https://www.sciencedirect.com/science/article/pii/S0168192323003854
https://link.springer.com/article/10.1007/s00704-024-05334-6
https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/ppa.13873
https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/ppa.14089
