CANOLA growers across the country are being urged to consider their harvesting options and maintain a degree of flexibility with the ongoing rains throughout spring and the summer of 2022-23 forecast to be wetter than average.

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.

The Bureau of Meteorology has said a La Niña event occurs when equatorial trade winds become stronger, changing ocean surface currents and drawing cooler deep water up from below.

This results in a cooling of the central and eastern tropical Pacific Ocean, but the enhanced trade winds also help to ‘pile up’ warm surface waters in the western Pacific and to the north of Australia.

The warming of ocean temperatures closer to Australia means the area becomes more favourable for rising air, cloud development and therefore rainfall.

The date of the monsoon onset in tropical Australia is generally two weeks earlier during La Niña years than in El Niño years.

As for the IOD, it is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.

Cooler sea surface temperatures in the western Indian Ocean relative to the east mean winds become more westerly, bringing increased cloudiness to Australia’s northwest and more rainfall in the Top End and southern Australia.

Some La Niña events occur at the same time as a negative IOD and when they do, rainfall is above average over large parts of Australia.

For example, during the strong La Niña in 2010, a negative IOD also developed, and these events combined to produce heavy rainfall and widespread flooding across eastern Australia.

Most climate models predict La Niña will deepen in November, before retreating through December and returning to ENSO-neutral by early 2023.

Both influences will increase pressure on farmers with a canola harvest - and on weather forecasters to predict windows of fine weather.

The idea behind windrowing canola and harvesting it later with a pickup front is to manage the risk of grain loss due to shattering from rain 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.