How to manage frost

Frost has been reported to various degrees in cereal, canola and lupin crops in parts of WA’s central, eastern and south-eastern grainbelt in the past two months.

Growers in susceptible areas remain on alert, as the risk period has been brought forward by earlier plantings this year.

Department of Agriculture and Food WA is encouraging growers to continue to be on the lookout for symptoms of frost damage but not to be alarmed about its impact.

DAFWA affirmed frost symptoms might not be obvious for up to 10 days after a frost event and damage tended to be patchy, with variability in a paddock.

Early-sown crops, low-lying areas and light-coloured soil types are typically most at risk and areas should be checked first.

Decisions about what to do with damaged crops should be based on an understanding of frost damage levels and economic aspects.

Grains Research and Development Corporation has acknowledged the potential implications of frost on crop production, investing in a range of projects now under the umbrella of its National Frost Initiative.

The five-year project is giving growers a combination of genetic, management and environmental solutions to help mitigate risk.

Cereals are the most sensitive of the winter crops to frost and yield losses from frost can occur from damage during and after flowering and at the early stages of booting.

Canola and pulses are at the highest risk of reduced yields from frost during the period from early flowering to late pod growth, but most yield losses occur after flowering and during early seed fill.

Frost damage in all crops can change with soil type, aspect and elevation, so it is advisable to check plants in different parts of an affected paddock.

GRDC NFI management program leader Dr Ben Biddulph said the first step in determining what to do after a crop had been frosted was to inspect and assess the damage.

For cereals, the recommendation was to collect random samples of heads across the paddock to estimate if any yield loss has occurred and to determine the extent of any damage. If a severe frost was suspected, growers should inspect and monitor crops for up to two weeks after the event.

To check on pulse and canola crops, peel open flowers and pods to see affected parts.

Research and experience in WA has found early frost-damage identification is essential for ensuring optimum return isfrom a crop.

Detailed for cereals, pulses and canola frost-identification guides are available in the GRDC Back Pocket series and in Managing Frost Risk.

Key symptoms of frost damage in cereal crops include:

• A ‘white ring’ on the stem above the highest node and below the ear

• Blistering, cracking or shrivelling of the stem just above the nodes

• Bent or twisted stems

• Heads that are blighted

• Heads that appear more translucent across a paddock.

Key symptoms in pulse and canola crops include:

• Lupins - scorched and withered leaves; shrivelled or dead seeds

• Field peas - dead flowers; shrivelled seeds; blistered pods

• Canola - yellow/discoloured pods; scarred pods; flowers aborted; fallen pods.

If frost damage is identified, there are four main options for managing the crop to the end of the season:

1. Harvest the grain, based on gross margins that include harvest costs

2. Fodder conservation, including marketing hay

3. Graze the crop if in a mixed enterprise

4. Green or brown manure the crop.

Dr Biddulph advises that if damage has occurred outside critical periods in crop development, the best option may be to harvest the grain — as most cereals can produce new tillers to partially compensate for damaged plants. This is providing spring rainfall is adequate.

He says cutting crops for hay can be expensive and growers should have a clear path to market or a use for the hay on-farm before committing to this option. The economics of grazing, manuring and crop topping also needed to be analysed closely.

While it is useful to seek objective assessment of frost risk, it is important to avoid a one-size-fits-all approach to managing this risk, according to Dr Biddulph.

He says frost risk plans used by the case study growers tend to start with an assessment of their approach to business risk and close consideration of their property’s exposure to frost risk.

Several growers are identifying and compiling zones and/or maps that identify the range of frost susceptibility of paddocks for adoption of diverse or alternative agronomic practices or enterprises to spread production and financial risk.

For the future, the frost case study growers say they are keen for GRDC to continue funding genetics research into the development of more frost-tolerant wheat and barley germplasm and ranking current wheat and barley varieties for susceptibility to frost.

Through the NFI, frost susceptibility rankings have now been made available for most commercial wheat varieties used in WA to help growers compare varieties and time of sowing when planning frost risk management strategies. These can be found via this link.

The data is based on three years of national research into field-based frost damage, including at research sites near Merredin and Wickepin, and rankings can be accessed through the GRDC’s National Variety Trials website.