From 45 °C temperatures scorching Citrusdal citrus orchards to heavy rain disrupting fruit set in table grape vineyards, South African growers are becoming increasingly familiar with one of modern agriculture’s greatest challenges: weather extremes that place crops under severe physiological stress.

While much attention is traditionally given to controlling pests and diseases, plant stress has quietly become one of the biggest factors limiting crop performance, says Martin Booyens, an expert in biological crop solutions and Technical Marketing Specialist at InteliGro.

“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 believes that with increasingly variable weather patterns becoming the norm rather than the exception, preparing crops for stress is becoming just as important as reacting to it.

When the Weather Calls the Cops

The effects are already evident 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. Unexpected rainfall during critical growth stages creates 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 Citrusdalcaused 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.”

The result? Crops can appear healthy yet still fail to realise their full yield potential.

“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.”

The effects extend below ground, too.

“High temperatures suppress beneficial soil microbes responsible for nutrient cycling and healthy root development, while soil salinity makes it increasingly difficult for plants to absorb water and essential nutrients such as nitrogen, calcium and potassium.”

Biologicals: Beyond Another Spray Program

“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.”

This is where biologicals come into their own – not as rescue treatments once crops are already under pressure, but as preventative management tools that improve crop resilience before stress occurs.

Different biological products perform different functions. Some support the plant’s metabolism during periods of stress, while others help maintain cellular water balance during heat and drought. Beneficial soil microbes stimulate root growth, improve nutrient uptake and strengthen soil biology, while products containing amino acids supply compounds that would otherwise require significant energy for the plant to produce itself.

“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.”

Before the Stress Takes Hold

Timing, however, is everything.

“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 closely and make management decisions proactively. Biological products typically require between 48 and 72 hours before the relevant metabolic processes are activated within the plant.

Successful stress management also begins with getting the basics right. Booyens emphasises that biologicals cannot compensate for poor plant nutrition or inadequate crop management.

“There is little point in investing in secondary metabolites if your plants cannot photosynthesise properly.”

He encourages growers to first ensure that crops have the nutritional building blocks required for normal photosynthesis and protein synthesis before addressing crop-specific stress challenges with biological products.

Once those fundamentals are in place, biological programmes can be tailored to individual production systems. Amino acids may help crops recover after hail damage. Beneficial fungi such as Trichoderma can improve root development where soilborne diseases are problematic. During periods of excessive heat at flowering or fruit set, osmoprotectants such as glycine betaine can help plants maintain cellular stability and improve fruit retention.

“There is no one-size-fits-all programme,” Booyens says. “The solution depends entirely on the conditions on your farm.”

Rather than relying on a single product or intervention, InteliGro’s crop programmes integrate biological solutions with plant nutrition, soil health and crop protection according to the needs of each production system.

Good Decisions Start with Good Information

Booyens cautions growers against selecting products based purely on marketing claims or applying biologicals without expert guidance.

“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.”

Working with trained Crop Advisors is equally important, he adds, as biological products should form part of a broader crop management programme rather than be used in isolation. Growers should also ensure products are correctly registered under Act 36 of 1947 and seek advice from qualified advisors registered with CropLife South Africa.

Although some growers remain hesitant because biological programmes increase short-term input costs, Booyens believes this overlooks their long-term value.

Unlike conventional chemistry, which generally provides relatively short-lived protection, beneficial biological organisms establish themselves within the soil ecosystem over time. As these populations build, they continue supporting plant health and resilience, often reducing the need for repeated applications in subsequent seasons.

“You’re not simply buying another product,” he says. “You’re investing in a healthier production system.”

Farm One Step Ahead Of the Weather

Building resilience into crops is no longer simply another management option – it is becoming a defining feature of profitable, sustainable production.

“The growers who consistently produce high-quality crops in future will be those who prepare their plants before stress arrives, not afterwards,” says Booyens.

That preparation starts long before the forecast predicts a heatwave. It begins with understanding your production system, monitoring crop health and working with an integrated approach alongside qualified Crop Advisors to make informed decisions before stress takes hold.

Issued by: InteliGro