What's going on with frost?

Author: | Date: 20 Mar 2015

Take home messages

  • Frost is a recognised production risk but incidence and severity is hard to predict.
  • CSIRO data suggests the length of the frost season has increased across southern Australia.
  • Screening of wheat varieties to frost is underway to assess the range in genetic responses.
  • Sowing time is a key driver of yield and needs to be planned in relation to yield, frost and heat.
  • Tactics to reduce frost risk include matching varieties to sowing time and maturity through to burning, farm zoning and changing the enterprise mix.

Background

Growers are used to dealing with frost in southern NSW. Since the late 1990s major frost events have caused significant crop losses and financial pain for growers in this region. Management has adapted to manage where possible some of the risks associated with late season frost. However in 2014 an early frost caused significant damage. Following a wet start in autumn many crops grew quickly with above average temperatures during May and were more advanced than usual for the time of year. Crop tissue was soft having not been hardened up with any minor frost events during early winter.

This was then reversed with a severe run of 18 or more frost events during late July and early August causing stem frost in cereals, flower and pod abortion in canola through to complete crop death in lupins. Cereal crops that had finished tillering and had started to elongate (GS30) were hit hard by the cold temperatures. Crop damage was estimated at 40-90% due to tiller death. Recovery did occur with late tillers able to reshoot from the base of the stem but the hot dry spring ultimately limited their yield potential. In cereals early sown spring wheats suffered greater yield losses than barley especially in western areas of the region. In comparison to a head frost many crops were able to partially recover to yield at 40-60% of their water limited potential.

Early sown canola was variable in its response to frost with crops on long fallow or brown manure able to compensate and recover using stored soil water to produce more flowers or pods. Canola on cereal stubble was less resilient with many crops losing primary stems, and therefore, crops were unable to recover prior to heat and moisture stress taking its toll in spring.

Industry response

The mechanics of frost damage involve a cereal crop being exposed to temperatures at or below freezing (-2oC) at canopy height for extended periods of time during and after flowering. Damage can also occur at booting (stem frost) or during late grain filling. Temperatures are measured using a standard weather station known as a Stevenson Screen at a height of 1.2-1.5m above ground level.

The incidence of frost is known to be on the increase with CSIRO suggesting the frost window has broadened by as much as 40 days in southern NSW. Steven Crimp from CSIRO indicates that frost occurrence is linked to a long term southerly shift in position and intensification of the band of high pressure typically located over central Australia in spring. This combined with quicker phenology due to flowering and maturity occurring at a rate of seven days earlier per 1oC of warming will potentially increase the risk of frost damage.

Coupled with a warmer drier climate, frost adds another significant challenge to the complex job of grain production. The industry is aware of these issues and GRDC has estimated that frost is costing growers around $360 million in direct and indirect yield losses every year. In 2014 the GRDC set up the National Frost Initiative (NFI) which will run for five years tackling frost from several angles using a combination of genetic and management solutions with tools and information to better predict frost events.

The GRDC initiative will focus on three main aspects with frost:

  1. Genetics – ranking current wheat and barley varieties for frost tolerance and identify frost tolerant germplasm.
  2. Management – investigating if there are any management practices (including nutrition, chemicals for protection against abiotic stress, stubble burning, grazing and sowing direction) that growers can use to reduce the impact of frost.
  3. Environmental prediction – looking at the prediction of frost impacts on yield and mapping at the farm scale.

Screening of wheat and barley varieties led by Dr Tim March from University of Adelaide is already underway with sites at Wickepin WA, Loxton SA and Narrabri NSW. The project aims to identify frost susceptibility and provide rankings of current varieties. The initial focus was on the effects of frost at flowering but assessments now recognise the potential impact of frost at earlier developmental stages and during grain fill. This will determine if varieties differ in their window of sensitivity to frost but it is a long and arduous process as the relationship between sterility and yield loss is still unknown.

Figure 1. Range in frost induced sterility and wheat variety susceptibility ranking.

Figure 1. Range in frost induced sterility and wheat variety susceptibility ranking (Source: Micheal Laws, The University of Adelaide).

No varieties are tolerant and therefore ratings are based on a ranking of susceptibility. Under severe frost (for example -8oC) or multiple minor frosts (several nights of -2oC to -4oC) all varieties tested are equally susceptible resulting in up to 100% sterility in flowering heads.

Varieties essentially will be rated as very susceptible or susceptible and are not based on differences in phenology or flowering time. The rating refers to the relative susceptibility of varieties flowering at the same time. The rankings have not been linked to variation from frost damage during stem elongation or grain fill and are based on the variation in wheat varieties to maintain grain number under minor reproductive frost at flowering time.

Sowing time – matching variety to maturity

To quote the NSW DPI Winter Crop Variety Sowing Guide "yield drops 4-7% with each week of delay in sowing after the optimum time for a specific variety". Sowing at the start of a variety's preferred window will achieve higher yields at the same cost as sowing late. Sowing time therefore remains a major driver of yield in all crops with the primary objective to achieve a balance between crops flowering after the risk of frost has passed but before the onset of heat stress. The loss of yield from sowing late to avoid frost risk is often outweighed by the gains from sowing on time to avoid heat and moisture stress in spring.

Early sowing has been widely adopted by growers in recent years following research by James Hunt and others from CSIRO that aims to match sowing opportunities with maturity for higher yield. This work has proven that in the medium rainfall zone, long season wheats sown in mid-late April on average yield 0.8t/ha more than mid-fast varieties sown mid May. Early sown crops yield more because they are able to access nutrients and water from deeper in the soil profile, develop a canopy faster which reduces evaporation but more importantly have a longer yield formation phase with an extended period of stem elongation.

This was proven correct in 2014 with winter wheat varieties such as EGA Wedgetail or Whistler sown mid-late April holding back their maturity during the May and remaining in the vegetative stage (tillering). These crops avoided any stem frosting due to the fact they were sown in the correct window for their maturity. Grazing of the winter wheats also delayed maturity and reduced their exposure to frost risk. Spring wheat (and barley to a lesser degree) sown early in the window (mid-late April) were unfortunately too advanced in maturity and subject to topography were unable to handle the frost events.

Understanding the maturity of any variety (including wheat, barley or canola) helps to determine what an appropriate sowing time is for your farm. Larger sowing gear, well-structured no-till soils and diligent fallow management now enables growers to plant efficiently by the calendar. This practice needs to be balanced against an understanding the maturity pattern of the crop types and varieties being sown. Aim to spread your sowing program over an extended period from mid-April to mid-late May utilising data from models such as Yield Prophet® or NSW DPI phenology research to help identify optimal sowing times based on historical data. The message is clear, only work daylight hours during sowing (leave the headlights off) and spread out the sowing program as highlighted in an example given in Table 1.

Table 1. Example sowing program for mixed farming operation at Osborne, NSW.

Date Crop Variety Comments
 1st - 14th April wheat Wedgetail,
Whistler, Wylah
Targeted for grazing, treat seed for aphids
 14th - 18th April canola Pioneer®45Y88CL  Ideal on fallow, higher yield potential with
stored soil water
 18th - 22nd April canola ATR Gem TT
Hyola®559TT 
Targeted on elevated blocks with grass weed
pressure
 18th - 25th April wheat Wedgetail,
Whistler, Wylah
Grain only
 25th - 28th April wheat Lancer, Bolac Long season spring wheats suited to elevated
blocks only
 27th - 30th April barley Hindmarsh,
Latrobe
Sow lower blocks in early May. Treat seed for
aphids, barley very responsive to early sowing
 28th April - 3rd May lupins Luxor, Wonga Very sensitive to frost during flowering, avoid
on low lying blocks
 1st - 5th May lucerne,
clover
Various Sow lucerne clovers alone or undersow with
barley or wheat
 5th May wheat Gregory Subject to elevation can sow earlier but delay
on lower blocks
 10th - 15th May wheat Suntop,
Spitfire, Trojan
Start with Suntop and Trojan finishing with
Spitfire in mid-May

 25th - 30th May field peas Percy Late sown to manage frost and bacterial blight
risk, option to cut for hay

Enterprise mix and farm zoning

An important tool that has been successfully adopted for managing frost risk is a range of enterprise options to spread financial risk in the event of frost damage. This is subject to the location of the business and skill set of the manager but the largest financial losses with frost have occurred where growers have a limited range of crop types or enterprises. Intensive cropping systems especially focused only on canola and spring wheat are often at the mercy of frost more than a diversified business as both crops are highly susceptible.

Barley has proven to be a sound addition to any crop rotation especially with its ability to handle frost better than wheat by flowering in the boot. Higher risk frost paddocks are suited to a higher proportion of barley in the rotation sequence in comparison to spring wheat. Barley is known to have approximately 2oC more frost tolerant than wheat whilst oats are 4oC more tolerant and present another alternative cereal and helps reduce production risk.

Cereal hay has been a sound strategy for dealing with frost events especially in low lying areas where grain production carries more risk. Producing and marketing cereal hay comes with more complexity than grain production but is a very useful tool for deriving income from crops affected by frost. The use of weather stations has helped growers to monitor temperatures in frosty areas especially for helping with the decision to make hay following an event.

Winter wheat varieties such as EGA Wedgetail, Wylah or Whistler can be used as a frost management tool in low lying blocks where frost risk is high. They can be sown early in the growing season and maturity delayed through grazing or sown later in their window such as early May so that flowering is pushed later to help avoid frost. The practice of sowing main season wheats very late to avoid frost is not recommended, as they often lack sufficient dry matter production during winter plus flower too late incurring yield loss due to heat stress.

Burning of stubble has produced mixed results across many trials but work from James Hunt in 2012 and 2013 found yield responses from burnt plots in contrast to where stubble was retained. The stubble had an insulating effect on the soil surface during frost events keeping the air temperature cooler for longer than the bare surface soil and this resulted in higher levels of frost damage. This highlights that in frost prone areas of the landscape burning offers another tool to help reduce the risk of damage especially in sensitive crops such as spring wheat and canola.

Pasture and livestock are ideal risk management tools for any cropping business that are aiming to manage frost issues. Sheep require an investment of capital, labour and skills to generate a profit but those growers who are geared up to run an efficient livestock operation are able to offset some of the potential losses that can occur with cropping and help stabilise a portion of their income.

Mixed farmers in undulating areas have successfully used farm zoning to manage frost by sowing low lying areas to pastures such as lucerne or grazing cereals, whilst cropping elevated areas more intensively. This can be done using elevation maps from the header overlaid onto yield maps or assessing paddock records over time to gauge areas that are consistently low yielding due to frost. Farm zoning is also useful for intensive cropping operations whereby they can rank each block based on elevation and subsequent frost risk. This could determine the range of crop types or varieties that suit individual blocks relative to a range of variables including soil type, rainfall, elevation and frost.

Frost and topography are now taken into consideration when land is valued and the impact it can have on the range of enterprises suitable for a specific property. Dryland cropping attracts a high level of risk and frost is a major consideration when potential buyers are assessing the capacity of a property in terms of its potential over the medium to long term.

Conclusion

Frost is a major issue for growers and advisers in southern NSW. 2014 was a new challenge dealing with a severe stem frost event early in the growing season, this contrasted with the usual frost risk that often comes later during flowering or grain fill. The industry and growers alike are looking at all the options available that will lessen the impact of these random yet devastating phenomena. Growers have a range of management tools that help reduce the impacts of frost subject to its severity and these need to be implemented to ensure recommended strategies such as sowing on time and targeting optimum water use efficiency are not compromised.

References

Crimp et al. (2015) ‘Jack’ of frosts – recent trends and drivers of change. GRDC, Adviser Update, Wagga Wagga.

Biddulph et al. (2015). Preliminary rating of wheat varieties for susceptibility to reproductive frost damage. GRDC, Adviser Update, Wagga Wagga.

Hunt et al. (2013, 2014, 2015). Strategies and tactics to extend whole farm water use efficiency – sow on time or early. GRDC, Adviser Update, Wagga Wagga.

Maccallum et al. (2015). The GRDC National Frost Initiative. GRDC, Adviser Update, Wagga Wagga.

Contact details

Greg Condon
PO Box 73 Junee NSW 2663
0428477348
greg@grassrootsag.com.au
@grassrootsag