Key points

• DPIRD trials have shown triazine-tolerant canola in March can be profitable as sowing in April
• March sowing is not better than April sowing, but may provide growers with more flexibility, as seeding opportunities become more irregular
• Risks, including poor crop establishment, seedling survival, frost at the end of flowering, predation and disease, need to be carefully considered when sowing early.

Changing cropping practices and increasingly unpredictable season breaks are prompting Western Australian growers to consider sowing canola earlier, but there is a lack of information for determining the risks and rewards of doing so.

To address this gap, a project led by the Western Australian Department of Primary Industries and Regional Development (DPIRD), with GRDC co-investment, undertook eight large field trials with four to five different times of sowing (TOS) from 19 March to 11 June in low and medium-rainfall sites in 2019 and 2020.

The sites were at Mullewa, Wongan Hills, Dale and Grass Patch. To generate data for early sowing in late-breaking seasons (6 June for 2019 for most sites), trials were irrigated prior to sowing, and as necessary to ensure crop survival post-seeding.

The canola varieties were all triazine-tolerant and included both open-pollinated and hybrid plant types with a wide range of variety maturities.

Rewards

Sowing in March produced profitable canola crops. Yields were highest in all trials when sown on 18 March or 8 April, and did not differ significantly at these dates (Table 1).

Table 1: Average yield (t/ha) for triazine-tolerant canola types at four times of sowing at three locations in Western Australia.

Source: DPIRD

At Dale, there was no significant difference between yields at the first three TOS in 2020 and the first four TOS in 2019, reflecting its longer growing season.

Average TOS yields ranged from 1.3 tonnes per hectare at Mullewa in 2019 to 3.5t/ha at Wongan Hills in 2020. There was a general trend for the oil content to decline with later sowing times. Gross returns followed the same pattern as yield.

Risks

Although March-sown canola produced similar yields to April-sown canola, there were greater risks. Higher soil temperatures in March reduced plant establishment at all sites. There was also greater risk of crop death with insufficient follow-up rain.

This risk was particularly important in warmer northern areas where, unlike other sites, trials needed regular light irrigation after emergence. Early sowing also increased the risk of damaging frosts at the end of flowering or during grain fill. A low incidence of frosts characterised 2020, contributing to the observed profitable yields with March sowing.

Frost-prone areas should be avoided for very early sowing.

Additional risks of March sowing come from predation and disease. Summer rains and an early break reduce the environmental risk of early sowing, but may lead to a green bridge and build-up of predator insects.

Diamondback moth (DBM) was difficult to control in the 2020 Grass Patch trial. Both DBM and green peach aphid are likely problems with early sowing due to the fastbreeding cycle in warm early sowing conditions. There is also greater risk of sclerotinia with early sowing due to longer flowering duration. Each risk needs to be evaluated for different environments before sowing canola early.

Other strategies to reduce risks of very early seeding are sowing only part of the canola program in March, increasing the sowing rate of open-pollinated canola, and regular monitoring for pests and diseases.

More information: Jackie Bucat, 08 9368 3481, jackie.bucat@agric.wa.gov.au; GRDC Update paper 2021 When to take advantage of early seeding opportunities for canola in WA