Frost effects on cereal species during 2017

Take home messages

• Heading and flowering are considered the most sensitive stages for frost damage in cereals, however, damage can still occur from the onset of stem elongation and this can be reduced through management and variety selection.
• Winter varieties have a long vegetative phase so have the lowest risk of damage from stem frost and although are not always the highest yielding varieties, may be the most stable across sowing dates.
• Recovery from stem frost can be achieved where there is moisture available to support new tillers.
• Matching phenology and sowing date is just as important for oats and barley as it is for wheat. Oats and barley are not resistant to frost damage.

Background

A common practice to avoid losses from frost is to avoid heading and flowering during the frost risk period (Frederikset al. 2015; Fulleret al. 2007). Matching phenology with sowing time is a method used to ensure sensitive reproductive stages of development escape severe frost events, while also aiming not to flower too late as to incur water stress during grain fill (Figure 1). In frost prone parts of the landscape, this is still relevant (Leske et al. 2017) and this flowering window typically occurs around early October in southern NSW. The early stem elongation stage is less susceptible to frost than heading and flowering as lower temperatures are required for damage to occur. Stem elongation however, usually occurs in a higher frost risk period so damage can still occur.

Anecdotally, over the past few seasons stem elongation frost damage has occurred across significant portions of the southern production system in SA, VIC and NSW in 2014. There has been a recent increase in frost severity and duration across southern Australia (Crimp et al. 2016) combined with the widespread adoption of earlier sowing of cereals, which has all contributed to the increased exposure of cropping programs to frost damage.

Figure 1. Susceptibility of wheat to frost during the development cycle (GRDC, 2016).

Of the three main cereal species grown in southern and Western Australian grain production zones including southern NSW, oats and barley have traditionally been categorised as being more tolerant to frost than wheat (Knightset al. 2017). However, the different phenological traits, overall plant characteristics and locality of where these species are grown in the landscape often make the ability to compare between them for frost susceptibility difficult and there is little data to support this claim. These claims have been made primarily based on observations of frost events that occur during flowering, but cereals are sensitive to frost damage both before and after flowering (Figure 1) and the final grain yield is the cumulative effects of all the individual frost events throughout development. To look at which crop type by maturity class combinations are most suitable for frost prone parts of the landscape, an experiment designed by GRDC’s National Frost Initiative assessed the variability in frost damage between varieties, within species and across four times of sowing.

2017 season

The 2017 growing season of southern NSW experienced an above average number of severe frosts. The trial site at Wallacetown (15km north east of Wagga Wagga) recorded 112 mornings below zero degrees throughout the growing season with 87 of these days having temperatures drop below -20C (measured at crop height in an unshielded Tinytag). Screen temperatures were on average two degrees warmer than those measured within the crop canopy. This emphasises the fact that crops experience colder temperatures than those generally recorded by weather stations as previously reported by Frederikset al. (2012). The growing season rainfall (April-October) was 199mm, well below the average of 321mm, but there was above average rainfall for the month of October.

Figure 2. Minimum daily temperatures from the trial site measured both within at the top of the crop canopy using unshielded Tinytag data loggers (TGP-4017, manually moved up in 10cm intervals through the season) and inside a Stephenson’s screen located on the paddock edge.

Method

The trial site was located at Wallacetown north of Wagga Wagga, NSW (-34.947905, 147.449482). It consisted of four times of sowing — 11 April, 20 April, 4 May and 25 May. Six varieties of wheat (Emu Rock, Scepter, Cutlass, Trojan, EGA_Eaglehawk and Kittyhawk), three varieties of barley (La Trobe, Commander and Urambie) and three varieties of oats (Bannister, Mitika and Durack) made up the crop type x time of sowing experiment. Varieties with reasonable performance across southern NSW and Western Australian production systems were selected to represent the different maturity classes within each crop type.

Results and discussion

Stem elongation

Sowing on 11 April saw quick developing wheat and barley varieties such as Emu Rock and La Trobe reaching the start of stem elongation (GS31) in mid-June, four weeks earlier than winter type wheat and barley varieties such as Kittyhawk and Urambie (Table 1). The sheer number and severity of frosts experienced during the 2017 season resulted in all varieties, regardless of maturity type, being exposed to frost during stem elongation, however, the faster developing varieties were exposed to a greater number of frost events whilst in the sensitive stem elongation phase and as a result suffered severe yield penalties.

Slow developing winter wheat and barley varieties exhibited stable yields across all sowing times. The vernalisation requirement in these varieties slowed the time to stem elongation (GS31). This allowed the winters to avoid some of the stem frost damage (Tables 1 and 2).

Figure 3. The relationship between the onset of stem elongation (GS31) and yield (t/ha) for the three cereal species used in the Wallacetown trial. The incidence and severity of frost events measured at canopy height (shown in light grey bars) provide an indication of the number of frosts experienced by the crop when stem elongation occurs too quickly.

Table 1. Days to beginning of stem elongation (GS31) for varieties used at Wallacetown, 2017.

Yield

Delaying the start of stem elongation through varietal selection and sowing time increased grain yields (Figure 3). Yield was stabilised across all sowing times through the use of winter type varieties. Kittyhawk wheat and Urambie barley with their relatively long vegetative period, achieved similar results across sowing dates, with yields between 4t/ha and 5t/ha (Table 2).

In the earlier sowing dates, the yields achieved by the spring varieties such as Emu Rock and La Trobe were due mostly to regrowth. Early formed tillers that developed rapidly to stem elongation were killed by frost (in season observations, samples still being processed). These plants then relied on grain from regrown tillers which was made possible by rain in late October that supported grain-filling. Varieties such as Scepter and Cutlass yielded well across all sowing dates, showing some flexibility in the 2017 season; undoubtedly attributed to the capture of late rainfall assisting grain-fill of late formed regrowth.

The poor performance of the oats in the first two sowing dates with yield starting to improve in the latter two sowing dates is due to limited phenological differences in the oat varieties used. All three varieties have fast to mid-fast development and hence should be sown mid to late May in frost prone areas to avoid exposure to frost during sensitive development stages.

Despite the regrowth contributing a substantial amount of grain in early sown spring cereal varieties, it caused sporadic and staggered flowering times which could not be precisely measured. This led to delayed maturity as green regrowth continued to develop through to late November and early December for the wheats. Yield was supported by the regrowth, however, harvest then became an issue as immature spikes and stems resulted in high moisture levels and a delayed harvest. In 2017, late rains favoured yields, but led to a decline in quality and accessibility.

Table 2. Grain yield (t/ha) of the 12 varieties from the four times of sowing (TOS) at Wallacetown, 2017.

^*VF - Very Fast, F - Fast, MF - Mid-fast, M - Mid, MS - Mid-slow, S - Slow, W - Winter

Conclusion

It is difficult to predict the environmental conditions that a crop will experience in a given season. Choose a variety that will perform well in the area and can be sown in a timely manner that will allow it to reach sensitive stem elongation, heading and flowering stages post frost risk period. In light of stem frost events in 2014 and 2017, attention should also be paid to matching sowing date and phenology to avoid early stem elongation. Winter varieties performed well in this trial having the most stable yields due to their longer vegetative phase.

Faster developing wheats, such as Scepter and Cutlass, showed flexibility in the sowing dates in 2017 as the late rainfall allowed regrowth after stem frost in the earlier sowings to mature. This is the first year of this trial, and samples are still being processed and analysed, hence further research coming out of 2018 will improve our understanding of how frost interacts with different cereal species.

Useful resources

Frost Risk Fact Sheet

Managing Frost risk tips and tactics

References

Crimp, S., Gobbett, D., Kokic, P., Nidumolu, U., Howden, M., & Nicholls, N. (2016). Recent seasonal and long-term changes in southern Australian frost occurrence. Climatic Change, 139(1), 115-128.

Frederiks, T. M., Christopher, J. T., Harvey, G. L., Sutherland, M. W., & Borrell, A. K. (2012). Current and emerging screening methods to identify post-head-emergence frost adaptation in wheat and barley. Journal Of Experimental Botany, 63(15), 5405-5416.

Frederiks, T. M., Christopher, J. T., Sutherland, M. W., & Borrell, A. K. (2015). Post-head-emergence frost in wheat and barley: defining the problem, assessing the damage, and identifying resistance. Journal Of Experimental Botany, 66(12), 3487-3498.

Fuller, M. P., Fuller, A. M., Kaniouras, S., Christophers, J., & Fredericks, T. (2007). The freezing characteristics of wheat at ear emergence. European Journal of Agronomy, 26(4), 435-441.

GRDC. (2016). Managing Frost Risk.

Knights, S., Belford, R., & Juttner, J. (2017). GRDC's National Frost Initiative - 2017 Southern Update. Paper presented at the Grains Research Update.

Leske, B., Nicol, D., & Biddulph, B. (2017). Optimising sowing time in frost prone environments is key to unlocking yield potential of wheat. Paper presented at the Perth Agribusiness Updates 27-28th Feb, Crown.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both experiment co-operation, NSW Department of Primary Industries and the support of the GRDC through the National Frost Initiative — the author would like to thank them for their continued support.

A sincere thank you to the Gollasch Family at Wallacetown for their cooperation and support with the trial. Thank you to Hugh Kanaley, John Broomfield, Greg McMahon, Cameron Copeland and Tom Quinn for their technical assistance and Karyn Reeves (Curtin University, SAGI West) for statistical advice.

Contact details

Hayden Petty
NSW Department of Primary Industries, Wagga Wagga
0447825052
hayden.petty@dpi.nsw.gov.au
@NSWDPI_Agronomy