Jack Frost is not welcome
Crops halved due to dry, frosty conditions
THERE has been plenty of media chatter in recent weeks, not about the forgettable 1988 thriller movie Jack’s Back, but the potential 2017 winter crop horror story starring the enigmatic Jack Frost.
Frost risk is an accepted part of growing winter crops in Australia. Every season, somewhere across the country, grain production is lost to frost.
The extent of those losses vary from year to year according to location and landscape factors as well as the climate.
Clear, calm and dry nights following cold days are the precursor conditions for a radiation frost (or hoar frost).
These conditions are most often met where high pressures follow a cold front, bringing cold air, accompanied by settled, cloudless weather.
When the loss of heat during the night decreases the temperature at ground level to zero, a frost occurs. Wind and cloud reduce the likelihood of frost by decreasing the loss of heat to the atmosphere.
The extent of frost damage is determined by how quickly the temperature takes to get to zero, the length of time it stays below zero and how far below zero it gets.
A frost event during flowering can cause sterilisation of the floret.
In general, wheat is more susceptible than barley to such events due to the length of its flowering period. That said, very few cereal crops are at the flowering stage so it is too early to see wide-scale frost-aborted flowers.
However, it is not too early to suffer stem frost damage.
Stem frost occurs when a small amount of water settles inside the leaf sheath above the penultimate node and adjacent developing tissue of the boot.
Many reports emanating from the Riverina region of
❝ However, it is not too early to suffer stem frost damage. — Peter McMeekin
southern New South Wales relate to the morning of August 28.
The overnight low in some areas was reported to be less than - 6 degrees, with below-zero temperatures for more than six hours.
Similar reports are also surfacing in the Murray Mallee region of South Australia.
Identifying stem frost damage can be very difficult and it usually takes quite some time for the extent of such events to become evident to the market.
Cereal losses of up to 70% have been reported, but such examples are few and quite isolated at this point. The one bright light is that affected plants, depending on available moisture, will send up new tillers to compensate.
In northern NSW and southern Queensland, frost damage to the chickpea crop is widespread. Many paddocks have been flowering for weeks and frequent frost events are taking their toll.
Chickpeas have a low tolerance to frost. However, as long as the plant can access sufficient moisture, they will simply reflower and produce new pods, minimising overall production loss.
In 2016 the rain didn’t stop until late October and the chickpea plants reflowered for weeks. This year almost the entire chickpea growing region has had less than 40% of average rainfall since April 1.
This simply means the plants will not have moisture to replace abandoned flowers and significant production losses will result.
The lack of rainfall and recent frost damage means this season’s production will fall to less than 50% of last year’s record.
It is the extent and the geographic spread of the damage that will tell the tale in terms of lost production.
POOR SEASON: Last year’s record chickpea crop will be a distant memory this year thanks to a challenging season for growers.