Frost can devastate blueberry crops, leading to significant economic losses. By harnessing digital agronomy growers are able to stay vigilant and aware of potential frost events, and can act accordingly to mitigate the impact of frost on their blueberry plants.

Blueberries in protected environments

While much of berry production in North America remains open-field, Europe and Northern Africa lead the way in covered cropping for blueberries. Growing in tunnel houses provides many advantages:

• Blueberries grown in tunnel houses require significantly less water for cultivation.
• The improved environment provided by tunnel houses increases productivity and fruit quality.
• Tunnel houses provide better production earliness compared to open fields, allowing for a strategic market advantage and better selling prices.
• Blueberry crops are protected from adverse weather conditions, ensuring a more consistent and reliable production while minimizing the risks associated with unpredictable weather events.

Susceptibility of blueberries to cold and frost

Despite being cultivated in tunnel houses, blueberries are highly susceptible to cold temperatures, particularly during budding, blossoming, and fruit development. Even brief exposure to frost can cause irreversible damage to the delicate plant tissues, compromising overall plant health and reducing yield potential.

During the budding stage for example, frost can damage emerging flower buds, resulting in reduced fruit set and yield potential. Similarly, frost during the flowering stage can kill blossoms, preventing pollination and fruit formation, ultimately leading to crop loss.

For highbush blueberries crop loss is likely to occur when temperatures drop below -2.2°C (28°F). The extent of freeze injury onset varies depending on the developmental stage.

A blueberry plant’s tolerance for cold generally decreases as flower bud swell progresses. Exposed flowers are damaged at temperatures below -6.7°C (20°F), and complete flowers are killed at temperatures below -3.9°C (39°F).

Blueberry blossoms may sustain corolla damage at temperatures below -1.1°C, affecting pollination and fruit development. Damage occurs at temperatures of -2.8°C (27°F) when blossoms are open. The plant is most sensitive during the period after corolla drop but before berry swelling, with a just a few minutes of exposure below -2.2°C (28°F) needed to cause significant damage. Enlarging berries are similarly susceptible at this temperature.

Invisible effects of frost on blueberries

For blueberries, frost damage may not always be readily apparent. After exposure to harmful temperatures, complete flowers or small fruits may develop a water-soaked appearance, shrivel, and eventually drop. However, even a brief period of cold can result in damage solely to the pistil. In such cases, the damaged pistil or a portion of it may turn brown, hindering pollination and fruit set.

Ovules, which mature into seeds within the berry, can also be harmed without any external signs. Healthy ovules are typically plump and white, but cold injury can cause them to turn black. If a significant number of ovules or young seeds are blackened, it is likely that the flower or fruit will fall off. Conversely, if only a few ovules are damaged, fruit development usually continues, albeit with delayed ripening and smaller size compared to berries with a greater number of healthy seeds.

Additionally, frost during fruit development can cause physical damage to the berries themselves, resulting in reduced size, quality, and overall marketability of the harvest. Understanding the specific effects of frost at each stage of blueberry growth is essential for growers to implement targeted protective measures and minimize crop damage.

Current frost damage prevention methods in tunnel house farms

In today's tunnel house farms, growers utilize a variety of digital agronomy tools and technologies to monitor and manage frost risk. One such farm is African Blue, Morocco’s largest producer of blueberries.

The FarmRoad digital agronomy solution was installed which included climate sensors in the tunnels in their farms. The sensors placed strategically throughout the tunnel house provided real-time data on air temperature, humidity and other environment metrics enabling African Blue to track fluctuations and anticipate potential frost events. African Blue also used these climate sensors to set up WhatsApp alerts in FarmRoad for when frost was imminent.

These digital agronomy tools gave African Blue the ability to make the decision to deploy heaters and potentially vents in the greenhouses that were threatened, or not, based on the data and without having to travel to the farm.

This streamlined approach resulted in significant savings for the growers in terms of staff time, fuel, and resources. Additionally, it empowered senior managers by providing real-time awareness of ongoing activities, enabling them to verify that timely and informed decisions were consistently being made.

Horticultural Manager, Aziz El Kahlaoui explained:

“Before, if the weather forecast indicated frost, my team would have to travel to the farms and manually check the temperature.“

“But now – with the alerts via WhatsApp we can more successfully manage our response to potential frosts and disease-risk. For me, and also for other senior managers it's a help to have these sent to my phone so I can check with the farm manager that they are making the right decisions for the situation.”

Since deploying FarmRoad, African Blue have enjoyed improved harvests and greater efficiency in the allocation of staff and resources.

Mitigating the risk of frost damage to your blueberry crop

To mitigate the risk of frost damage, blueberry growers can implement a variety of proactive measures. Installing frost protection systems such as overhead irrigation, wind machines, or heaters can help raise temperatures and prevent frost formation within the tunnel house. But none of these are effective without real-time crop management software, like FarmRoad, to determine when these measures should be implemented. Only with a full picture of plant health, environment and farm performance can modern growers effectively protect their blueberry crops from the detrimental effects of frost and ensure a successful harvest in controlled environments.