IN-SEASON STRATEGIES TO MANAGE FROST

Year two is now underway with a series of trials exploring agronomic options in those areas more prone to frost events. Historically, a lot of frost work has focused on finding genetic tolerance to frost. This Grains Research and Development Corporation (GRDC) investment Enhancing frost tolerance and/or avoidance in wheat, barley and canola crops through in-season agronomic manipulation, led by FAR Australia (FAR2203001RTX), aims to explore ways to improve frost tolerance by manipulating crop phenology and improving frost resilience using novel agronomic practices

There is no easy answer, and a frost that causes 90% damage in one year is hard to weigh against 10 to 15% damage from heat and water stress in most years Preliminary APSIM runs that consider frost, heat and water stress suggest that in an El Niño year, the better outcomes are from crops that flower before the heat and water stress. Paradoxically, this means taking on slightly more frost risk in an El Nino year and hence reinforces the need to have salvage plans for dealing with a frosted crops

In summary, the ‘right’ frost decisions depend on the farm and grower. A grower still has to weigh up the reward and regret of optimism against the reward and regret of caution Decisions are improved by knowing frost risk across the landscape, knowing about flowering windows and having options to soften the regret through hay and/or grazing.

The three main strategies are:

1. Using mechanical defoliation or grazing to delay flowering. This project is pushing the limits by cutting the crops back to 5-10 cm above the ground and defoliating later than normal to remove or impede the developing apex (Z31 in cereals, bud visible in canola).

2. Applying plant growth regulators at early stem elongation to slow crop development

3. Applying cryoprotectants and bactericides to manage the frost damage caused by ice nucleating bacteria.

All strategies are being tested on fast developing wheat, barley and canola.

CSIRO are modeling crop development after defoliating wheat crops established at different times, with the aim of defining the optimum defoliation intensity and timing across different cropping regions.

Many aspects of the trials are exploratory as there has been little work done with these interventions and products with regards to frost. Some products used in the trials are already commercially available for other uses, though not yet registered for use on wheat, barley or canola crops.

More flexibility to hit the flowering period

These options would also give growers more flexibility with variety choice and sowing time to hit the optimal flowering period. The project is assessing how these agronomic interventions can delay development into avoid frost risk and still flower in the optimal flowering period before heat and drought stress

Bonnie Flohr (CSIRO) says, “grain yield is more sensitive to stress during flowering, so the whole idea of the optimal flowering period is to target the lowest risk of heat, drought and frost. Hitting the optimal flowering period means aligning the time of sowing with cultivar development ”

But what if an early sowing opportunity arises?

The ideal choice is to sow a slower developing variety that can still hit the optimal flowering period. If a slower developing variety isn’t available, a grower could potentially use these agronomic options to slow development and still hit the optimal flowering period. A win-win of sorts

If these interventions prove useful, growers could be more tactical in their cultivar choice, for example, “You could sow a fast cultivar early, then delay flowering using the strategies so that it acts like a winter wheat,” says Bonnie.

The project is experimenting on fast developing wheat, barley and canola but are growing slower developing cultivars alongside them that will not be sprayed or defoliated. This is to compare how the agronomic interventions delay development compared to slower developing varieties.

Next steps

With a late project start and mild season, 2022 was largely based on pilot trials and controlled environment research. This year the project is ramping up, with full-scale trials continuing until the end of 2024

Max says, “This year there are more field experiments going in across the country, with a range of sowing times from early sowing to late sowing. Some of the plant growth regulators, bioprotectants and bactericides that were tested in lab conditions in 2022 are going into the field this year.”

And while no one wishes a frost upon a farmer, a few frosts this year would help put these strategies to the test.