Risk rankings add new pieces to frost jigsaw

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Key messages

  • New frost performance value rankings enable varieties of wheat and barley to be compared for their frost susceptibility at the reproductive stage.
  • Yield loss information to match the frost values will be determined in future research.
  • No wheat or barley varieties are frost-tolerant, although barley is generally less susceptible.
  • Under severe frost (for example, –8°C) or multiple minor frosts (several nights of –2ºC to –4ºC) all varieties tested to date are equally susceptible, resulting in up to 100 per cent sterility in flowering heads.
  • The preliminary frost performance values should be used to manage the frost risk of new varieties after they are selected, based on how known varieties of similar performance are managed.
  • Variation in reproductive frost susceptibility has not been linked to variation in susceptibility to stem frost, experienced in 2014 across southern Australia, or to frost during grain filling.

Is there a frost-tolerant wheat or barley variety available? This is the question often asked of scientists working on frost management in Australian cropping systems. The answer unfortunately, at this point in time, is ‘No’.

However, several years of research investment by the GRDC has established a robust field-based process to determine the susceptibility of wheat and barley varieties to frost at the most vulnerable development time (around flowering).

The research has determined that wheat and barley differ in their response, with barley being less susceptible. Current wheat and barley varieties have been ranked for their relative susceptibility to frost at several sites around Australia. However, the full range of response in both species is yet to be determined. Identifying tolerance is part of ongoing research.

Frost exerts a complex production constraint in cropping systems and requires a package of risk-management strategies. These strategies should include pre-season, in-crop and post-frost management tactics.

Crop selection is just one component of a comprehensive frost-management plan and fine-tuning the selection of a variety through knowledge of its frost susceptibility ranking is a subset of this component.

Rankings explained

Large, dedicated frost-screening nurseries in frost-prone environments near Loxton (South Australia), Merredin and Wickepin (Western Australia) and Narrabri (New South Wales) have been established to measure susceptibility to minor frosts at the reproductive stage with great accuracy and repeatability.

The trials are managed by the University of Adelaide in collaboration with the Department of Agriculture and Food, WA (DAFWA), and Statistics for the Australian Grains Industry (SAGI). They are funded under the GRDC’s Australian National Frost Project, which forms part of the GRDC’s multidisciplinary National Frost Initiative.

The frost performance values have been developed from frost susceptibility data generated at these sites from the 2012, 2013 and 2014 seasons. Information collected in future years will be added to the database.

The values are primarily to compare varieties for their frost susceptibility at flowering and can be viewed using an interactive tool at the National Variety Trials website.

Reproductive frost damage is defined as intermittent or partial floret sterility. The sterility is often the combined effect of cold, desiccation and freeze damage to the floral organs and developing grain (GS45 to GS71) from minor frosts at this critical phase of development (Figure 1). This is also often referred to as floret, flowering or head frost damage.

No wheat or barley varieties, as yet, have been found to be frost tolerant. Under severe frost (for example –8°C) or multiple minor frosts (several nights of –2°C to –4°C) all varieties tested to date are equally susceptible, resulting in up to 100 per cent sterility in flowering heads.

A particular variety has been given a performance value relative to other varieties that flowered at the same time during a series of frost events in that site and year.

The performance values are for the relative susceptibility of varieties to frost when flowering at the same time. The values do not take into account the frost risk associated with the flowering of a variety given its sowing date.

Time line of susceptibility showing wheat to frost during its development cycle

Figure 1Susceptibility of wheat to frost during its development cycle.

Using the information

Growers need to continue to select varieties based on the best yield, market value (quality type), maturity, and agronomic and disease performance. Once a variety has been selected, use the frost performance values to fine-tune risk-management based on how known varieties with similar performance are managed.

For example, a grower in the WA Upper Great Southern may be considering how to incorporate Corack and LongReach Scout into their cropping program to replace Wyalkatchem and Yitpi.

From a frost-risk-management point of view, growers can treat Corack in the same way as Wyalkatchem or Mace given its similar sowing/flowering time to Mace. Corack can essentially be treated the same in terms of sowing time and position in the landscape.

On the other hand, LongReach Scout, although similar in frost performance to Yitpi, flowers about five to seven days earlier so may need to be sown slightly later than Yitpi to manage frost risk comparably to Yitpi.

It will continue to be critical to ensure flowering occurs within the optimum flowering window to minimise frost risk, to ensure the entire program does not flower at the same time and to manage flowering time in relation to heat and terminal drought. The frost performance values need to be used within this context. 

Tools such as DAFWA’s Flower Power or Yield Prophet® need to be used in conjunction with the frost performance values.

To date, varietal differences in susceptibility to frost during stem elongation and grain filling have not been confirmed or linked to variation in reproductive frost susceptibility, on which the frost performance values have been developed.

The reproductive frost values are based on the ability of wheat varieties to maintain grain number under minor frosts at flowering time. Under these reproductive/floret or head frosts, grain number is the main yield component affected and therefore normally corresponds to yield performance.

However, this may not be the case if there is a long growing season, or in early sown/flowering crops, or if varieties are able to compensate differently through late tillers, enhanced grain weight in lieu of lost grains, synchronisation of flowering time and plasticity of grain number.

Further research undertaken within the GRDC’s National Frost Initiative will validate the yield relationship between compensation ability, reproductive frost damage and grain yield (DAW00234) and compensation ability (CSP00180).

Updated management plan

A new Frost Management Tips and Tactics is available from the GRDC website.

The risk of frost varies between years as well as across landscapes and growers should reassess their individual situation and management strategies on an annual basis. This new Frost Management Tips and Tactics provides guidelines for growers to tailor their individual frost-management plans. It puts the use of the wheat and barley cultivar frost susceptibility values in to a farm management context.

More information:

Two men standing in a crop field facing the camera

Dr Tim March (left) and Dr Ben Biddulph.

PHOTO: University of Adelaide

Dr Tim March,
0467 709 236,

timothy.march@adelaide.edu.au;

Dr Ben Biddulph,
0428 920 654,
ben.biddulph@agric.wa.gov.au

See frost performance values on the National Variety Trials website

Frost Management Tips and Tactics

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Variety the spice of early crop life

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GRDC Project Code UA00136, DAW00234, CSP00180, UW00005

Region South, West