Paddock Practices: Managing canola harvest to minimise rain risk

With the upcoming spring and 2022-23 summer forecast to be wetter than average, canola growers across the country are being urged to consider their harvesting options and maintain a degree of flexibility.

In September 2022, the Australian Bureau of Meteorology declared both a negative El Niño Southern Oscillation (ENSO) – or La Niña – and a negative Indian Ocean Dipole (IOD) to be in effect. Both these climate drivers are associated with above average rainfall, especially in eastern Australian.

Most climate models predict La Niña will deepen in November, before retreating through December and returning to ENSO-neutral by early 2023. For growers in South Australia and Western Australia, IOD predictions are similar with the possibility of a deeper phenomenon before the system breaks down with the arrival of the summer monsoon.

Both influences will increase pressure on the canola harvest – and on weather forecasters to predict windows of fine weather.

Rain brings additional risks

The idea behind windrowing canola and harvesting it later with a pickup front is to manage the risk of grain loss due to shattering as the pods mature and dry. It means the greatest handling shocks are applied to semi-mature pods, while the fully ripened windrows feed directly into the harvester.

Direct harvesting ripe plants carries a greater risk of pod shattering and grain loss both before and during harvest. However, wet conditions can introduce other risks that may make direct harvesting the more conservative option.

If windrows remain wet for more than three days due to rain or even very wet ground, there is a significant risk of the grain sprouting. In even worse cases, ponding or flooding could destroy the entire windrow.

Windrows may also be vulnerable to rodents this year, especially in regions coming off the back of a mouse plague or a run of high-yielding seasons.

Finally, growers who use windrowing contractors may feel pressure to have their crop cut when it may not be quite ready. Fewer fine days can concentrate the demand for contractors and make growers reluctant to miss an available booking.

Consider soil conditions

After a very wet winter and spring, rain during harvest is not the only concern. Paddock trafficability can also significantly affect how canola is harvested.

Unless aerial spraying is an economical option, spray topping requires paddocks, or at least tramlines, that can support a heavy sprayer. However, using firm tramlines in an otherwise soft paddock carries its own risks. If heavy machinery strays or slides off the hard tracks, it may become bogged.

As paddocks dry out, they will need to be able to support a windrower and then a harvester.

Exactly how and when the paddock is harvested may be driven by what machinery can operate on it and at what time. The effect of machinery on trafficability for subsequent machines should also be a harvest consideration.

For example, there is no point in spraying or windrowing if that operation will make the paddock impassable for the following windrower or harvester.

Decision points for managing risk

In typical years, canola harvesting can be a relatively protracted process, taking 10 days or more across spray topping (or desiccation), windrowing, then collecting and threshing with a harvester.

In wet years, rain presents a significant risk that increases with the duration of the harvest process.

Growers can reduce this risk by using rain forecasts to identify a suitable ‘fine weather window’ before starting the harvest process, or by choosing a harvest method that will minimise exposure to rain.

Some steps in the harvest process can be skipped if the weather is not conducive. For example, it is relatively simple to forego spray topping and start the harvest with windrowing. If wet weather makes windrowing risky, it may be safer to wait a few more weeks and direct harvest.

Spray topping risks

Spray topping can be useful for controlling weeds in the crop and promoting pod desiccation.

Once a crop has been sprayed, it generally needs to be cut and windrowed within 7-10 days, then picked up and threshed another 7-14 days after that. It may be possible to skip windrowing and direct harvest a sprayed crop, although pod condition needs to be watched closely in order to harvest before the pods become too dry and shatter prone.

Spraying immediately before or after significant rain can influence its effectiveness and produce unpredictable results.

Windrowing risks

The main risk when windrowing crops, apart from those of rain and rodent damage, is that the windrows must be picked up and threshed once they are ripe – usually 7-14 days after cutting – to minimise sprouting.

If significant rain is forecast during this period, consider direct harvesting where possible as this will reduce the negative effect on seed quality.

Paddock trafficability should also be considered. If windrowing could make the paddock impassable for the harvester, switching to direct harvest may be a better option.

Direct heading risks

Reaping ripe canola certainly carries a greater risk of pod shattering and grain loss. However, direct heading may deliver better results overall if windrows are badly affected by rain.

Direct heading provides a harvest option that can be accomplished later in the season, when the weather and soil may be drier. It also offers more flexibility for harvest timing and can be started and stopped at short notice if weather conditions are marginal.

Direct heading equipment

Rigid table auger and draper fronts are both suited to direct heading canola, and extendable table fronts work well but are not considered essential.

For smoother harvesting, use a tyne reel and run the reel as slowly as possible to minimise shattering and pod drop. A cross auger will help the material to flow along draper belts and increasing the angle of the draper will help with feeding. Retractable fingers may need to be adjusted to stop the material tangling around the table auger.

Finally, if wet conditions have caused the crop to lodge, use crop lifters set to just below the height of the lowest pods.

For more information on machinery set up and tips to reduce shattering, refer to the GRDC Direct heading canola fact sheet.

*Possibly less, subject to withholding periods.

Monitor seed colour closely

Canola harvest decisions are closely linked to seed colour change, with 60 to 80 per cent colour change being the typical optimum timing for windrowing. Waiting beyond this point will increase the risk of the pods shattering at windrowing.

Seed colour inspections become critical in the period leading up to harvest. This season, growers are encouraged to start a schedule of regular inspections now so they can establish the rate of colour change as well as the maturity of their crop.

If rain is forecast, understanding how quickly the crop is maturing can be a valuable tool for deciding whether the harvest process can be delayed, should be brought forward, or will need to be modified in favour of direct heading a few weeks later.

Growers who need to change their usual harvest program to manage weather risks but are unsure about the specific timing or techniques for their conditions, are encouraged to consult their agronomist or adviser at the earliest opportunity.

More information

Rohan Brill, Brill Ag
Phone: 0488 250 489
Email: rohan@brillag.com.au

Mathew Dunn, NSW DPIPhone: 0447 164 776
Email: Mathew.dunn@dpi.nsw.gov.au

Useful resources

• GRDC Grains Research Update: 2021 Rethink your approach to canola harvesting to optimise crop performance - GRDC
• GRDC Fact Sheet: Direct heading canola factsheet
• Windrowing and harvesting – Australian Oilseeds Federation
• GRDC Grow Notes – Canola
• GRDC video: Grower experience of direct heading in canola, Victoria
• GRDC publication: Canola best practice management guide for south-eastern Australia