Climate change presents a number of challenges for Australia’s $15 billion horticulture sector, including, perhaps surprisingly, frost. Paradoxically, the warmest decade in recorded history has seen some of the most widespread and serious frost damage to commercial crops in both Australia and North America.
Jeff Rohrlach, managing director of Agrobest, says that while horticulture is less susceptible to the impact of frost than broadacre, frost doesn’t always happen when it’s expected and unseasonal changes in weather do happen.
“In longer-term crops like fruit orchards and grapevines the risk is much higher, especially as climate change turns previously ‘safe’ planting sites into areas susceptible to winter damage,” he said.
“Research suggests that the frost window has widened over the past two decades, especially in the eastern and southern parts of Australia, despite an overall increase in mean minimum temperatures.
“This means that frost will be more likely to occur in the future: the risk period will start earlier and finish later. Even tropical North Queensland has seen unseasonal frost this year.”
Mr Rohrlach said the pattern of later endings is consistent across much of southern Australia, while the earlier starts are more localised to western NSW and northern Victoria.
“The frequency of extreme cold temperatures is also on the rise across much of southern NSW and northern Victoria. An average increase of four frost days and five cold nights each decade has been identified since 1970.
“The location of frost events is also changing. The band of high pressure which normally sits across southern Australia has moved further south and intensified, allowing cold polar air to move onto the continent following the passage of any cold fronts.”
How does frost damage occur?
Not all frost is created equal, Mr Rohrlach said.
“Frost occurs on clear nights, often in early spring, when the air temperature drops to 2°C or less. But the amount of damage it causes depends on a combination of factors, including the stage of plant development (the potential for damage is much higher around flowering), how quickly the night time temperature plummets, how low it goe s and how long it stays there.
Changing climate with more frost days in recent decades, combined
with a common plant bacteria can lead to extreme crop frost damage.
“When the air around plants is moist, ice crystals form on the surface of the plant. Water in between plant cells freezes and draws water out of surrounding cells to form more ice. If this frost melts slowly, crops can recover from the damage, but this is less likely with a quicker thaw in spring, when damage can be severe.
“When the air is dry, the situation is even more dire. In this situation, ice cannot form on the plant surface. The water between cells freezes quickly and forms large crystals. These crystals create holes in the cells and recovery is not possible. If this type of frost affects a flower or developing ovary, yield can be negatively impacted.”
Mr Rohrlach said one of the reasons that frosts can rip holes in plant cells is a usually innocuous bacteria found all over most plants. “On a typical day, the bacteria have no negative effect on a plant – but when the temperature drops, it creates big problems, because it leads to the formation of icy spears inside the plant cells.”
Protecting your crop
Mr Rohrlach said there are three key approaches to in-season management of frost risk: managing the temperature; physical barriers; and spray on protection. A fourth, which is often overlooked is the management of various nutrient levels within the plant.
Crops can be effectively shielded against frost damage through a variety of approaches,
including simple-to-use, Australian-made spray-on products like Envy.
“Products like AgroBest Envy have been shown in trials to deliver significant frost protection to a wide variety of crops. Envy is the market leading frost product in the horticulture sector – for good reason.
“AgroBest’s innovative products utilise a proprietary technique, based on R&D conducted in Australia, to dramatically improve plants’ frost tolerance. They do this by disabling the bacteria which cause ice shards to develop in plant cells.
“Envy is a unique water-emulsifiable polymer concentrate, which can be used on most trees, vegetables and flower crops. When dry, Envy forms a semi-permeable, biodegradable film, which reduces transpiration and protects plants from climatic extremes. It can increase frost tolerance by as much as 4°C and reduce moisture losses through transpiration by up to 50%.
“Envy is extremely simple to apply and available from a range of resellers. AgroBest works hard to maintain fast order fulfilment of 4–5 days when products are not stocked, plus Envy is stable for storage so growers in frost prone areas can be confident the product will remain effective if purchased and stored to ensure availability when frost does occur.”
