Frost Protection in Kiwifruit

It’s that time of the year again, and in early September we saw the soft green tissue come out of dormancy. On cool spring nights Southern Cross Horticulture (SCH) Establishment and Cropping Orchard Managers are out protecting our world class orchards from frost risk.

Frost is a risk to kiwifruit from bud break until mid-October. Without frost protection, when a frost occurs and the air temperature drops below 0°C, it causes the intracellular and extracellular water in the plant to freeze. The freezing of water in the plant cells causes the water to expand, bursting the plant cells through water expanding. This causes death of the plant cells and irreversible physiological damage to the plant. Even minor frost damaged cells reduces the surface area of the plant available for photosynthesis, which limits plant growth, ultimately reducing crop yield and orchard returns. Therefore, frost protection is a vital part of looking after SCH orchards.

Two widely used methods of frost protection include overhead sprinklers and frost fans:

- Overhead sprinklers protect plants from frost damage by covering the plant surface area with water at a correct rate onto the canopy. This slowly builds a layer of ice over the plants, insulating the plant tissue by keeping in heat instead of freezing the plant.

- Frost fans are used to protect orchards from frosts by transferring heat from the warmer air above the orchard in the inversion layer and pushing it down to the colder air closer to the ground and vines. This protects the kiwifruit plants by increasing the air temperature of the canopy.

Quintin Swanepoel, a Cropping Orchard Manager, explains what a typical frost night involves. “On a typical frost night, Orchard Managers are woken up by alarms from their phones, which are set off by temperature sensors within the canopy which detect low temperatures on the orchard. This then give us enough time to reach the orchard before the temperature is below 2.5 degrees. Once Orchard Managers are woken up by their alarm, they have to check in with the frost coordinator, Russell Dunstan, confirm that we are awake, aware that temperatures are low, and are on our way to the site.

Once we get to the orchard, we check in again and we confirm with Russel we are on site and monitoring temperatures. This usually involves taking a temperature probe and checking the low spots of our orchards, where we know that temperatures get the lowest, by testing leaf tissue and bud temperatures. We then check and wait until the temperature gets low enough to warrant either starting our frost fans or running our overhead irrigation.

Throughout the night Russell will monitor temperatures of all SCH orchards, as well as frost fan and diesel pump statuses remotely, to ensure everything is running smoothly and make sure that if there is a frost risk on an orchard the responsible Orchard Manager is there on site ready to run the frost protection system.

As the frost protection system is running Orchard Managers will move throughout the orchard and make sure that frost fans, overhead sprinklers, and tow and blows (moveable frost fans) are all working correctly. Once all systems are running well, and everything is protected, we can check on other orchards or do other work during the night.

When the temperatures are high enough and we can confirm the temperatures are safe, we then turn off the frost protection systems and pre-programme them onto the automatic settings”.

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