South Africa's increasingly frequent weather extremes are placing crops under growing physiological stress, with agricultural specialists warning that environmental conditions are becoming as significant a threat to yields as pests and diseases.
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From temperatures exceeding 45°C in Citrusdal's citrus orchards to heavy rainfall disrupting fruit set in table grape vineyards, growers are facing production challenges that require a more proactive approach to crop stress management.
Climate pressure on crop performance
According to Martin Booyens, technical marketing specialist at InteliGro, climate change has fundamentally changed the production environment, making plant resilience an increasingly important part of successful crop production.
"Stress is the silent thief of yield," says Booyens. "Conventional crop protection remains essential, but it is no longer enough on its own. A more holistic approach is required. Climate change has fundamentally changed the production environment. Today, one of the greatest threats to yield is often not insects or diseases, but the plant's inability to cope with environmental stress."
Booyens says the effects are already visible across South Africa's production regions.
Regular heatwaves in table grape areas such as Kakamas and De Doorns have resulted in poor fruit set, uneven bunch development and reduced yields, while unexpected rainfall during critical growth stages has created additional production challenges.
During the past citrus season, Valencia orchards experienced significant fruit drop after crops came under stress during key developmental stages, while temperatures exceeding 45°C in Citrusdal caused sunburn, oxidative stress and lower fruit quality and pack-outs.
"These are physiological stress responses," says Booyens. "When stress strikes, plants switch from production to survival. Energy that would normally drive growth, flowering and fruit production is redirected simply to stay alive. Photosynthesis slows, enzyme activity becomes restricted, and harmful reactive oxygen species begin damaging plant cells."
He says heat also disrupts water balance within plant cells, increasing oxidative stress and creating conditions that can leave crops more vulnerable to disease.
"Heat places further pressure on plants by disrupting water balance within individual cells. As moisture is lost, cells shrink and microscopic cracks can develop, creating entry points for pathogens. At the same time, salts become more concentrated inside plant cells, further increasing oxidative stress and cellular damage."
Booyens adds that high temperatures also suppress beneficial soil microbes responsible for nutrient cycling and healthy root development, while increasing soil salinity makes it more difficult for plants to absorb water and nutrients such as nitrogen, calcium and potassium.
Preparing crops before stress occurs
Booyens believes growers should focus on preparing crops before stressful conditions develop rather than responding once visible damage has occurred.
"Growers often respond to stress by adding more chemistry," says Booyens. "Those products have an important role, but they are generally designed to solve a specific problem, not necessarily to restore the plant's physiological balance or strengthen its ability to cope with future stress."
He says biological products can support crops in different ways, including helping maintain cellular water balance during heat and drought, improving root development, enhancing nutrient uptake and supporting plant metabolism during periods of stress.
"If a plant is experiencing a severe heatwave, it's using virtually all its energy simply to stay alive," Booyens explains. "Providing amino acids allows the plant to redirect that energy towards recovery, growth and strengthening itself."
Timing, he says, is critical.
"These are not products you apply once your crop starts wilting," says Booyens. "By the time visible symptoms appear, much of the physiological damage has already occurred."
Instead, growers should monitor weather forecasts and make management decisions proactively, as biological products typically require between 48 and 72 hours before the relevant metabolic processes are activated within the plant.
Building long-term resilience
Booyens stresses that biological programmes cannot compensate for poor crop nutrition or weak management practices.
"There is little point in investing in secondary metabolites if your plants cannot photosynthesise properly."
He encourages growers to first ensure crops have the nutritional building blocks required for normal photosynthesis and protein synthesis before addressing crop-specific stress challenges with biological products.
Depending on production conditions, amino acids may assist crops recovering from hail damage, beneficial fungi such as Trichoderma can improve root development where soilborne diseases are present, while osmoprotectants such as glycine betaine can help crops maintain cellular stability during periods of excessive heat at flowering or fruit set.
"There is no one-size-fits-all programme," Booyens says. "The solution depends entirely on the conditions on your farm."
Data-driven decisions
Booyens cautions growers against selecting products based solely on marketing claims or using biologicals without expert advice.
"You need to understand what is happening in your soil, your water and your crop. Good crop decisions start with good information. Regular soil, water and sap analyses help remove the guesswork, allowing management decisions to be based on what's happening in the field rather than what might be happening."
He says biological products should form part of a broader crop management programme developed alongside qualified Crop Advisors, with growers also ensuring products are registered under Act 36 of 1947.
Although biological programmes can increase short-term input costs, Booyens says their long-term value lies in improving soil health and crop resilience.
"You're not simply buying another product," he says. "You're investing in a healthier production system."
As weather extremes become more frequent, Booyens believes proactive planning will become increasingly important.
"The growers who consistently produce high-quality crops in future will be those who prepare their plants before stress arrives, not afterwards."
