Key points

• Frost is a major risk for canola production
• The impact of frost has proved difficult to research
• New methods for crop ‘frost exclusion’ are being developed

A pilot research project has tested the use of mobile shelters as a way to develop more field-relevant methods of quantifying frost damage to canola crops. The research has been made possible through a Grains Agronomy and Pathology Partnership co-investment project supported by NSW DPI and GRDC. The two-year project is addressing knowledge gaps in frost risk management.

Frost has become a major impediment for the Australian canola industry due to increased frequency of extreme climatic events and exposure of early sown canola to greater frost risk. Although agronomic solutions for frost are evolving, a genetic solution has proved more elusive. This may have been partly due to the challenge of developing field-relevant methods of quantifying frost damage with reference to frost-free control plots.

Previous research in frost used multiple sowing dates to create a range of flowering times to examine the impact of frost. However, commercial relevance of the experimental results was questioned as true ‘non-frost’ treatments were usually missing. Recently, automated diesel heat pumps were developed as frost controls in cereals. However, actively heating larger canola canopies would be too demanding for the pumps.

Instead, purpose-built mobile frost shelters (three metres long by 1.8m wide by 1.2m adjustable height) were constructed from black plastic layered with insulation sheets fitted on a metal frame. These shelters were rolled over designated ‘control’ plots in field trials when frost was forecast to enable a side-by-side in-field comparison between frost-affected crops and non-affected crops.

As temperatures at crop canopy height can be two or more degrees lower than forecasts, frost damage can occur when 2°C or lower temperatures are forecast by the Bureau of Meteorology.

Canola frost research

Canola is most susceptible to frost damage during reproductive development from bud to grain-filling stage, but frosts at late flowering or grain-filling can be severely detrimental. Spring frosts that occur in September at grain-filling are the most economically damaging, resulting in reduced grain yield and oil quality. In 2017, frost reduced canola grain yield by approximately 0.3 tonnes per hectare in NSW alone – a total of 120,000t valued at $63 million (estimated farmgate at $525/t).

In a replicated field experiment, four canola varieties with two temperature treatments (frost and non-frost) were investigated in growing season 2021. Frost exclusion treatments were imposed during the entire reproductive growth stage and pods were tagged to mark any frost events to capture the effect of frost on seed development. This research will be critical to quantify direct yield loss due to frost and the commercial implications of frosted crops.

Preliminary results showed that mobile shelters were successful in creating frost exclusion in mild frost (–2°C), enabling field-based comparison between frosted and unfrosted plots. The shelters now need to be tested under severe frost conditions when temperatures fall below –4°C.

Along with frost shelters, the research team is using a controlled-environment facility to further understand frost damage using different intensity and duration of frost at critical growth stages of canola.

By developing a greater understanding of temperature thresholds for frost stress and the impact of frost during optimum canola flowering dates growers will be able to better mitigate frost risk.

The methods and protocols developed in this pilot project will be useful for frost/chilling tolerance in all grain crops, not just canola.

More information: Dr Rajneet Uppal, rajneet.uppal@dpi.nsw.gov.au, 0436 341 649