It appears that how you use water is more important than how much you use when trying to protect vines from the impact of heatwaves.
Two projects being run in the Riverland by the University of Adelaide are producing quite dramatic results when applying specific cooling techniques rather than just leaving the everyday irrigation running for longer.
Delivering water directly to the roots and surrounding soil the night before a summer scorcher can reduce daytime canopy temperatures by as much as 5°C below ambient temperatures. Using misters to lightly spray the canopy during the heat of the day is even more effective, dropping the temperature by 10–12°C.
The techniques are quite different, but each achieves the aim of ensuring vines do not shut down even when temperatures hit the mid 40s – which is contrary to previous thinking. And, according to project leader Dr Vinay Pagay, even if you have to use them these techniques 5 or 6 times a year it will only increase your water usage by 5 per cent.
‘Both are very efficient techniques’, he said. ‘If you just turn on the tap 20 per cent more you only see a temperature drop of 1–2 degrees during the day, but with our under-canopy sprinklers it’s 5 degrees and with misters 10–12 degrees. That’s a huge difference.’
The water used is additional to normal irrigation because the trials show that neither technique influences soil moisture or vine water status. ‘Even with the night watering we aren’t altering the water availability to the vine. We are using almost all of that water for evaporative cooling through the soil.’
Misters are more effective but also a little more expensive to install and the mister heads have to be removed before pruning or harvesting as they can get tangled in machinery. An automated system is used so misters will turn on and off at regular intervals. On the hottest days, temperatures rise quickly once the misting stops.
Watering in the evening is less expensive because growers already have irrigation systems in place. All that’s needed is to install sprinklers to wet the inner and mid rows.
Misters also are not recommended with very saline water, as salt can clog them and there is a risk of leaf burn. Disease does not seem to be an issue, however.
‘One grower concern is increased incidence of botrytis or the mildews because you are wetting the canopy but we’re not seeing that. We’re working in the Riverland and at the Waite in Adelaide – when it gets hot enough to warrant using misters the water doesn’t stay on the fruit or leaves for very long.’
Dr Pagay said both techniques would be particularly valuable in warmer inland regions where heatwaves could be regular, long and damaging. However, they would also be of use when growing premium fruit in any region, as any spell of hot weather could cause the loss of important aromas and flavours in the fruit.
Delivering water directly to the roots and surrounding soil the night before a summer scorcher can reduce daytime canopy temperatures by as much as 5°C below ambient temperatures.
Using misters to lightly spray the canopy during the heat of the day is even more effective, dropping the temperature by 10–12°C.