Frost-affected crops in spring: assess your options

With wet conditions forecast for many production regions across southern Australia this spring, it’s important for producers to be pragmatic in their approach to assessing their crops after frosts, according to Lisa Castleman, cropping agronomist with Riverina Local Land Services.

Lisa said the future of these crops may be very different than if they experienced a frost in a dry season.

"The main options for frost-affected crops are usually to turn them into hay or silage for sale, feed your own livestock, graze them off, or to leave and harvest with a reduced yield," she said.

“However, the reduced trafficability in the paddock in a wet season and the prospects of a La Niña change everything.”

"In all of the past severe frosts, we’ve seen crops cut for hay unnecessarily. With prospects for good spring rainfall and where there has been good crop nutrition, there’s more potential for later tillers to realise grain – so take the time to examine crop damage carefully,” Lisa said.  

To determine the best option, Lisa recommends a step-by-step approach:

1. Assess the damage using a hands lens or a magnifying glass. Lisa's tips for damage assessment include:

• Make a judgement based on a minimum of two field assessments, with the key being the time between assessments.

• The assessment interval after a frost event will be 5–10 days, depending on the maturity of the crop and the seasonal conditions for growth. Aim for an interval that covers anthesis (opening of the flower bud) and grain fill. If the damage is from a stem frost, the emerging head will fail to emerge but can be seen by dissecting the stem above the node.
• The inspections may be a week or a fortnight apart. Severely damaged plant tissue will turn white before it starts to rot. Healthy plant tissue which has survived the frost will remain green and continue to photosynthesise.
• You won’t be able to see the plant’s response to frost at the first inspection. The plant will want to re-allocate resources and may send out later tillers or shoots from the base. In a longer spring with follow-up rainfall and milder temperatures, these late tillers can advance to maturity very quickly.

• Appraise the crop in front of you. Each paddock is different and can be affected by sowing date, variety and elevation. Inspect the more susceptible low parts of the paddock first, then progress to higher areas of the paddock.

2. Apply realistic calculations to potential yield as grain or fodder.

• Learn how to correctly estimate cereal crop yields by watching this video demonstration.

3. Establish your herd or flock’s nutritional needs – if they can be met by grazing crops, or consuming hay/silage or frost-affected grain, consider:

• The impact of changing your animals’ diets. Consult a livestock nutritionist when introducing canola hay or silage.
• How you’re going to manage hay or silage production and storage, including quality control and moisture content.

4. Seek professional advice from industry specialists, such as agronomists or farm consultants, and make decisions based on research.

• Consider all options, including grazing – a salvage decision can still be a smart decision.
• Opportunities could arise to manage a weed problem with cutting or brown manuring an affected crop, or continuing through to harvest to produce feed quality grain (remember to conduct a feed quality test to avoid grain being undervalued).
• If a crop doesn’t proceed to harvest, leave a standing test strip for final yield evaluation.

Tools and resources

Canola

• Frost identification guide for canola and pulses, GRDC
• A video on the options for frost-affected canola crops, NSW DPI
• Canola hay and silage – cutting time and feed quality fact sheet, NSW DPI
• Canola hay and silage fact sheet, Grains Research and Development Corporation.

All crops

• Crop salvage calculator, NSW DPI
• Publications, tools and resources on grazing crops and decision making resulting from the MLA-supported Grain & Graze 3 project

Livestock nutrition

• Feeding and Nutrition Guide, NSW DPI
• Making More From Sheep's ‘Turn Pasture into Product’ module
• More Beef from Pasture’s drought preparedness tool

Supply chain integrity

Understand the impact of treatments on fodder, hay, grazing crops and grain for stock feed and the need to manage grazing and withholding periods prior to slaughter by reading the Livestock Production Assurance requirements.