Summary

With a range of genetically modified canola technologies and varieties now available in South Australia, many growers are unclear on how these varieties and technologies compare to traditional options. Herbicide regime trials and variety trials were run to help Mid North growers understand how genetically modified canola varieties could best fit into their farming systems.

Background

Genetically modified (GM) canola varieties can offer growers a range of benefits including improved weed control, particularly where herbicide resistance is a problem, and potentially higher yields. Growers need on-the-ground demonstrations of how the new canola technologies and varieties can best fit into Mid North farming systems and which herbicide regimes for annual ryegrass provide the best control and return.

Research Aims

The core objectives of the project were to:

• Demonstrate genetically modified (GM) canola variety options and where they best fit into Mid North farming systems.
• Determine what herbicide regimes offer the best return for annual ryegrass control.

In The Field

Four herbicide regime trials were run over three years at Hart and Spalding (2021) and Hill River (2022 and 2023) in SA’s Mid North. Trials compared traditional varieties including conventional, Triazine Tolerant (TT) and Clearfield® (CL) varieties to GM varieties with Roundup® Ready, TruFlex, stacked tolerance (CL + TruFlex) and LibertyLink® (2022 trial only) technology. Glyphosate and/or glufosinate with mixing partners was applied to relevant GM varieties in a one or two-spray regime at the 2-leaf, 4-leaf or 8-leaf stage. Two treatments also had an application of glyphosate at first flower stage to evaluate a three-spray regime.

Canola variety performance was evaluated at Hart in 2021, 2022 and 2023. In 2021 and 2022, trials were randomised complete block designs for individual canola technologies, similar to NVT trial designs. In 2023, the trial was designed as a multistratum split-plot that enabled direct comparison of canola yield across different technologies.

Results

At Spalding in 2021, when annual ryegrass (ARG) populations were low, a single application of Roundup® Ready PL at the high rate (1.67L/ha) recorded similar ARG control to a single application at the lowest on-label rate (1.15L/ha).

Higher ARG populations were present in the wet conditions at Hill River in 2022. Roundup® Ready PL at the higher rate increased ARG control compared to the lower rate. A two-spray herbicide regime with glyphosate improved control compared to one spray. Single glyphosate applications recorded similar ARG control to CL and TT herbicide regimes, but control improved when more than one in-crop glyphosate application was made to TruFlex and stacked tolerance varieties. Liberty® herbicide with glyphosate or clethodim at the 2-leaf stage followed by Liberty® within 14 days recorded similar ARG control to glyphosate as a two spray-regime at Hill River in 2022.

Low rainfall at Hill River in 2023 meant single applications of Roundup® Ready PL (at the high or low rate) were sufficient to control ARG and follow-up applications were not economical. CL regimes recorded reduced control due to Group 1 and 2 resistance. TT regimes recorded similar control to single Roundup® Ready PL applications.

Numerous GM varieties yielded well across the three years of trials demonstrating their potential to return yields similar to or higher than traditional varieties (CL and TT). Conventional variety Nuseed Diamond, Pioneer 44Y94 CL, Nuseed Emu TF and Hyola Blazer TT were the highest yielding varieties across multiple seasons in each technology. Over two years of trials, RGT Baseline® TT, SFR65-064TT, Pioneer 44Y30 RR and InVigor® LR 4540P performed well.