RIVERLAND citrus producers had to wait a number of days to see effects from last week’s frosty conditions, however, a senior local industry figure says he has seen “very little” damage to fruit so far.
The Renmark Airport Weather Station recorded below zero temperatures everyday between Monday and Friday last week, with a -3.8C minimum on Tuesday being the second-coldest place in South Australia.
Citrus SA chair Mark Doecke said frost resulting from sub-zero temperatures could damage both the inside and exterior of citrus fruit.
“We’ve had three days in a row now of -4 or less,” Mr Doecke said.
“That poses a risk to fruit. It can cause skin blemish or internal fruit quality problems.
“It depends on what varieties you’re growing and where your fruit is, in terms of elevation… a few things effect how much damage you’re going to get.
“If the fruits in a bad place, the cold will freeze the little cells in the orange and when they unfreeze it dries out and you end up with a dry patch in the fruit.”
Mr Doecke said spraying fruit with a molasses mixture – containing high sugar levels – was effective in protecting oranges from freezing.
“You can see skin damage and there’s very little of that because of the molasses we’ve used,” he said.
“Molasses goes a long way to (preventing) the skin damage, but it won’t stop a smaller piece of fruit freezing internally.
“We’ve cut and we found very little damage internally and very little skin damage.”
A Bureau of Meteorology spokesperson said a lack of overnight cloud cover led to the Riverland’s stretch of below
zero temperatures.
“It was a pretty long stretch of sub-zero temperatures and frosty mornings over the Riverland,” the spokesperson said.
“That was caused by quite a persistent ridge of high-pressure.
“When we have a strong high-pressure system that means we have clear skies and light winds overnight.
“Because that persisted for such a long time, that really allowed for a lot of overnight cooling to happen because there was nothing to trap the heat in from the daytime.”
Mr Doecke said citrus varieties usually harvested later in the year – such as mandarins – were more susceptible to frost damage due to a lower sugar content.
“They’re at higher risk because the further you go into the season, the fruit sweetens up as it grows,” he said.
“The sweeter that fruit is, the less likely it is to damage because sugar has a lower freezing point.
“So a ready-to-pick orange is at a much lower risk than a green one that will be ready in September.”