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.¹

Horticulture is less susceptible to the impact of frost than broadacre, speaking generally, as most crops are grown to suit seasonal conditions. That means the crops most susceptible to frost are not in the ground when frost is likely – but 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.

Many growers are unaware that the latest spray on frost protection products, developed in Australia using leading-edge R&D, can dramatically reduce the risk of frost damage.

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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.² 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.

The pattern of later endings is consistent across much of southern Australia, while the earlier starts are more localised to western New South Wales and northern Victoria.

The frequency of extreme cold temperatures is also on the rise across much of southern New South Wales and northern Victoria. An average increase of four frost days and five cold nights each decade has been identified since 1970.³

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.

Not all frost is created equal.

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 number of factors, including the stage of plant development (the potential for damage is much higher around flowering), how quickly the nighttime temperature plummets, how low it goes and how long it stays there.

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.

One of the reasons that frosts can rip holes in plant cells is a usually innocuous bacteria that is found all over most plants. On a typical day, the bacteria has 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.

This bacteria, Pseudomonas syringae⁴ (p. syringae), causes damage by acting on specific proteins known as ice nucleation active proteins. P. syringae utilises ice formation to break the leaf’s surface, allowing it to thrive on the plant’s cellular nutrients. 

Pre-season

Knowing your property

The layout of orchards or vineyards is an important consideration and growers should take into account the contours of the land. This might mean planting the more frost-susceptible trees or vines on higher ground where cold air is less likely to accumulate, or creating dense windbreaks or trees planted across the slope to dam cold air and raise the level of damage higher up into the trees or vines. Creating gaps or planting dense windbreaks down the slope can facilitate cold air ‘drainage’ and reduce the impact of frost on crops.

Understanding your frost tolerance

Most commercial crops are sensitive to frost to some degree and horticultural crops are particularly sensitive to temperature, most having specific temperature requirements for the development of optimum yield and/or quality. Already growers plant annual crops to match seasonal conditions, but those conditions, and the time of those conditions, are changing.

During the season

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.

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.

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