In the coming weeks, as buds swell, and the season for many Australian growers kicks off in earnest, one of the first things to contend with is frost. We’ve heard stories of hard-working growers waking up every morning to check the Bureau of Meteorology weather stations, then heading out to thermometers hanging in their orchards at various “cold spots” to check whether the critical threshold has been reached. Others describe sleeping in their car, underneath the frost fans, so that it isn’t quite as far to go at 4 am in the morning to check temperatures, and get things underway to prevent an icy white blanket settling on the fragile newly emerged buds.
Frost forms when there is enough water vapour in the air, and when the temperature of a surface drops below the frost point temperature. That is the temperature below which water vapour from the air condenses onto your crops as ice (or frost), rather than as dew. And frost events tend to happen on clear, still nights, when the ground draws the last warmth from the air, and cold air sinks into low lying land, freezing the water vapour that comes into contact with the ground and with your plants.
What does all that mean? Well, by adding an air temperature and relative humidity sensor to your Plexus system, you can now let Plexus and Green Brain do the checking for you. Green Brain will even send you an SMS to let you know that a certain condition has been reached, so you can rest easy knowing that Plexus is watching over your crop and will let you know whether or not you need to get out of bed on a cold morning!
Talk to your local agent (or anyone at MEA, and we can put you in touch with them) about using the new air temperature and relative humidity sensor and SMS alerts to make managing frost easier.
Some useful starting points:
• The Bureau of Meteorology suggests that air temperatures below 2.2°C, measured at 1.2 metres above the ground, indicate a potential risk of frost forming at ground level.
• According to Abraham Izak Perold, who wrote ‘A Treatise on Viticulture’ back in 1981, one of the best predictors of frost risk is the dew point temperature after sunset. If it’s less than zero, be alarmed - there is frost likely. If the dew point temperature is higher than zero, then it’s more likely you’ll wake up to glistening dew than frost. So you can jump onto Green Brain at bedtime, and see whether it’s going to be one of those nights that you should turn the volume of your phone right up so that you won’t sleep through any SMS alerts!