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Help at hand for better frost decisions

Frost-damaged Vixen wheat.
Photo: George Pedler

On 12 September 2023, Lower Eyre Peninsula (EP) agronomist George Pedler was in a paddock in Ungarra, South Australia, checking a Vixen wheat crop for frost damage. Concerned about sub-zero temperatures a few nights prior, he wanted to check whether the crop had been affected and, if so, to what extent.

On close inspection, his fears were confirmed. Mr Pedler could see that frost had affected the stem of the wheat, destroying cell structure. A decision was made to cut the crop for hay.

The only silver lining, he says, was that the damage had been identified quickly. This meant that the crop was cut when it was most valuable, ensuring returns were maximised. This is an important factor in the Lower EP, where there is not much of a local hay market and freight costs can be $60 per tonne higher than in South Australia’s mid-north.

But there was another benefit to come from Mr Pedler’s paddock inspection. Knowing the importance of early and accurate frost damage detection, he uploaded photos and videos taken on his phone of the affected wheat to the Better Frost Decisions Facebook page.

A key feature of a GRDC investment managed by Mallee Sustainable Farming (MSF), the Facebook page is a dynamic community resource where growers and agronomists share their experiences, insights and management strategies around frost. By sharing his videos, Mr Pedler showed others what stem frost damage looked like and how to how to identify it.

As well as a practical resource, the page is also a valuable personal support. “It’s an extremely emotional event, frost,” says Mr Pedler, who works with individual growers and is one of five private agronomists working with grower group Agricultural Innovation & Research Eyre Peninsula (AIR EP) on the Better Frost Decisions project. “I think it's a great thing for people to realise they’re not on their own – that we have this network that we can go back to and share information or source information to help us through our decision-making.”

The frost challenge

Frost is a major issue for the Lower EP. Even if detected early, cutting frost-affected cereals for hay is not always a profitable option because of high freight costs, which bite harder as hay prices fall. There is also a shortage of cutting and baling equipment in the region, meaning timely hay production is not always an option.

“We haven’t got that ‘get out of jail free’ card of cutting for hay that other growers potentially do because of our location,” Mr Pedler says. “So, profitability-wise, we need to be right on to it and at the forefront of the research and any information that’s flowing through.”

Mr Pedler says there is a significant focus in the region on developing strategies to mitigate against frost damage. Research is being conducted by AIR EP through collaborations with GRDC investments including the MSF project and a National Grower Network (NGN) project looking into strategies such as soil amelioration.

We’ve got large areas of uniform (crop) maturity and therefore when a frost occurs, our exposure to risk is quite high.

Despite a relatively mild 2023, frosts are becoming more unpredictable and are a challenge to deal with, he says. Growers on the Lower EP have been dealing with frost events across August, September and October, making it difficult to schedule sowing times or varieties in order for them to reach riskier growth stages at safer times.

He says cropping practices and advances have also increased the risks around frost. For example, bigger machinery that works more efficiently has produced large areas of crops that mature at the same time, increasing frost risk in a greater number of plants.

“We’ve got large areas of uniform maturity and therefore when a frost occurs, our exposure to risk is quite high because the crops are all within critical growth stages for the same short period of time,” he says.

Meanwhile bigger canopies and stubble retention, while providing their own significant benefits, can increase the severity of frost by reducing the amount of sunlight and heat absorbed by the soil – heat that at night can behave like a buffer against frost.

Mitigation strategies

But research and technology are also helping to mitigate against frost impacts.

The amelioration trials are showing promise, he says, with deep-ripped soils staying slightly warmer than unripped soils, potentially mitigating frost.

“It’s been extremely effective and that’s great for where you can ameliorate your soil. But there’s also a lot of rock where people get frost, where you can’t put a ripper through. So that is why we are looking at other options as well.”

Paddock zoning is one of the most effective and simple strategies to mitigate against the impacts of frost, he says. Based largely on the work of agronomist Mick Faulkner, this involves using yield maps to zone paddocks as red, orange or green in terms of frost risk, and managing them accordingly.

With this knowledge, sowing times can be altered to avoid crops flowering during frost danger periods in the most at-risk paddocks. And combining early and late-flowering varieties in the same paddocks can also spread risk, although this can also result in a yield penalty to both varieties.

Fast-maturing wheat varieties such as Vixen can be a handy tool to spread risk, planted either early or late in a cropping program. And the new high-quality variety Mowhawk holds promise with a unique growth habit that means it can be planted early and not run to maturity too quickly if conditions are warm in autumn.

As season 2024 approaches, Mr Pedler says there are several factors to keep in mind to protect against the impact of frost. “Generally, the advice is to keep an eye on zoning, mix up your varieties, ameliorate your soils where possible and keep open with your communication – keep an eye out for your neighbour,” he says.

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