Frost damage concern for south-eastern Australia

Author: Rebecca Barr | Date: 01 Sep 2014

Growers and advisers are urged to get out in paddocks and check plants for frost damage after unusually low temperatures and widespread reports of impacted crops in the past fortnight.

While crops are commonly thought to not be susceptible to frost until flowering, with temperatures in some agricultural areas reaching -4°C (Figure 1) many crops in earlier growth stages have been affected.

BOM Map of temperatures

Figure 1: Widespread frost events have occurred across the south-east of Australia with minimum temperatures below -4oC in some regions. 

Source: Bureau of Meteorology

Damage has been observed in wheat, lupins and barley, but wheat has been most severely affected. Crops have been damaged at any growth stage from first node (GS31) onwards.

GRDC panel member and western New South Wales agronomist John Minogue has seen very severe crop damage in the West Wyalong region and north and west of the area.

“Reports are coming in from agronomists and farmers of widespread stem frost in cereals. Advanced lupins are also quite badly affected and the extent of damage to canola is unknown. The damage appears to have emerged after two frost events of around -4 degrees in the past month.

 “Large areas of crops were at the second node stage (GS32) and even as early as the head only a few millimetres from the boot being affected. There have also been reports of damage east and south of West Wyalong, but not to the same extent. There appears to be pockets of damage that were more advanced than most, generally those that were sown earlier.”

Growers inspecting crops for damage should look out for the following symptoms (Table 1).

Where frost is observed, there is no simple answer that experts can provide on the chances of the crop recovering.

Table 1: Symptoms of frost during early growth stages.

Source: Adapted from Managing Frost Risk: A Guide for Southern Australian Grains

 Crop growth stage  Inspection Details  Frost symptoms in wheat  Example
 Vegetative (before stem extension)
 Examine leaves
 Leaves are limp and appear brown and scorched.
Vegetative stem frost signs of limp, brown and scorched leaves
 Elongation (before and after head emergence)
 Pull back leaf sheath or split stem to inspect damage
 The stem has a pale green to white ring that usually appears sunken, rough to touch and soft to squeeze. The stem or nodes can also be cracked or blistered. Stems can be damaged on the peduncle (stem below head) or lower in the plant. If the head had emerged at the time of the frost then it is likely that the flowering parts or developing grain has also sustained damage. If the head is in the boot then ongoing monitoring is required to assess the level of damage.
signs of elongation frost with white rings on stems

Frost damaged floret

 Flowering and post-flowering
 Peel back the lemma (husk), inspect the condition of the florets (floral organs) in the head
 Flowering is the most vulnerable stage, because exposed florets cannot tolerate low temperatures and are sterilised. Grain will not form in frosted florets, but some surviving florets may not be affected. Pollen sacs (anthers) are normally bright yellow but become dry, banana-shaped and turn pale yellow or white.
Frost damaged floret with pale dry anther

Paddock of frost damaged wheat

Frost damage in wheat at Black Rock in the South Australian Upper North on the 19th of August.

PHOTO: Jim Kuerschner

University of Adelaide frost researcher Tim March says it is difficult to predict how crops may respond.

“If the majority of the heads are damaged in the majority of a crop it’s likely that the crop is not going to be worth harvesting. But where about 50 percent of the heads damaged, there’s no way to say what will happen. It depends on what’s happened within the vascular tissues of the plant, as well as the conditions for the plant between now and harvest, such as spring rainfall.”

GRDC Southern Panel member and YP agronomist Bill Long says growers need to consider their circumstances and decide quickly. Growers have a number of management options to consider (Table 2).

“Growers should inspect their crops to determine how severe the damage is so that they can make a decision on the way forward. If the conclusion is that harvesting won’t be economical, there are a number of options, and the best choice depends on a number of factors that the grower needs to assess with their agronomist,” he said.

“If the choice is to cut hay, then this is best done soon as hay quality is affected by significant rainfall events.” In doing this, it may be necessary to consider the current market situation. The GRDC has initiated a number of emergency measures to deal with the frost event (see What is your GRDC doing?).

Table 2: Management options for frost damaged crop, each with advantages and disadvantages. 

Source: Managing Frost Risk: A Guide for Southern Australian Grains

Options Potential Advantages Potential Disadvantages
Harvest Salvage remaining grain
More time for stubble to break down before sowing
Machinery available
may be greater than return
Need to control weeds
Threshing problems
Removal of organic matter
Hay / Silage Stubble removed
Additional weed control
Costs $35-$50/t to make hay
Quality may be poor
Nutrient removal
Chain / Rake Retains some stubble (Reduces erosion risk)
Allows better stubble handling
Costs $5/ha raking
Time taken
Graze Feed value
Inadequate stock to use feed
Remaining grain may cause acidosis
Stubble may be difficult to sow into
Spray Stops weeds seeding
Preserves feed quality for grazing
Gives time for final decisions
Retains feed
Retains organic matter
Difficulty getting chemicals onto all of the weeds with a thick crop
May not be as effective as burning
Boom height limitation
Expense $5/ha plus cost of herbicide 
Some grain still in crop
Plough (Cultivate) Recycles nutrients and retains organic matterbr/> Stop weed seed set
Green manure effect
Requires offset disc to cut straw
Soil moisture needed for breakdown and incorporation of stubble
Swath Stops weed seed set
Windrow can be baled
Regrowth can be grazed
Weed regrowth can be sprayed
Relocation of nutrients to windrow
Low market value for straw
Poor weed control under swath
Expense - swathing ($20/ha)
Spraying ($5/ha per herbicide)
Burn Recycles some nutrients
Controls serface weed seeds
Pemrits re-cropping with disease control
Can be done after rain
Potential soil and nutrient losses
Fire hazard
Organic matter loss

What is your GRDC doing?

Now

  • The GRDC held an emergency teleconference to discuss the impact of current frost events and will be conducting a series of regional workshops to extend information about potential management options for growers in affected areas.

Long term

The GRDC recently launched a national frost initiative focused on identifying and delivering practical genetic and management solutions to assist growers to manage the impact of frost. The three-pronged initiative will address:

  • Genetics – aiming to develop more frost-tolerant varieties.
  • Management – investigating if there are preventive products, stubble and nutrition management practices or other measures that growers could implement to reduce the impact of frost.
  • Environmental prediction - focusing on predicting the impact of frost events on crop yields and mapping frost events at the farm scale to enable better risk management.

More information

Francis Ogbonnaya, 02 6166 4500, francis.ogbonnaya@grdc.com.au

More Information:

John Minogue, 0428 763 023, jlminogue@bigpond.com

Bill Long, 0417 803 034, bill@agconsulting.com.au

Tim March, 08 8313 6700, Timothy.march@adelaide.edu.au

View the GRDC Frost booklet

GRDC Project Code UA00136, CSP00143

Region South, North