Summary

Field and pot trials were conducted to investigate the environmental conditions that impact the control of annual ryegrass (ARG) by Liberty® herbicide in canola with the LibertyLink® technology. Research showed that humidity following application has a big impact on the efficacy of ARG control glufosinate. Liberty® was most effective against ARG when used at higher rates, applied to small weeds and when humidity is high, temperatures are moderate and light intensity is adequate.

Background

A range of genetically modified canola technologies are available that offer alternative weed management opportunities, particularly where herbicide resistance is an issue. LibertyLink® canola technology is tolerant to Liberty® (Group 10) herbicide. The active ingredient in Liberty® is glufosinate, a new product in broadacre agriculture, and growers and advisers needed a better understanding of the environmental conditions that affect efficacy against ARG.

Research Aims

The core objectives of the project were to:

• Better understand the environmental conditions that influence control of ARG with glufosinate herbicide.
• Provide spraying strategies for successful and increased weed control of ARG.

In The Field

Field trials to evaluate the efficacy of glufosinate herbicide under field conditions were run at Hart and Hill River in the Mid North in 2023.

The Hill River trial tested 16 Liberty® application strategies including application rate, water conditioners, timing, mixing partner (clethodim or glyphosate) and low temperature conditions.

The Hart trial investigated the impact of ARG growth stage on Liberty® efficacy and included two rates of Liberty® standalone as well as tank mixes with clethodim or glyphosate.

Two pot experiments were also conducted at Waite in collaboration with Plant Science Consulting to evaluate the influence of temperature and photoperiod on sequential applications of Liberty® on three biotypes of ARG – susceptible; resistant to Group 1 (DIMs); and resistant to Group 1 and Group 9 (glyphosate).

For the DIM resistant ARG biotypes, the efficacy of Liberty® at two growth stages (2-3 leaf and 3-4 tiller) and three temperature regimes for 24 hours post-spraying (warm, cold and outdoor temperatures) was also investigated.

Results

Treatments that included Liberty® tank mixed at the lowest label rate with clethodim or registered glyphosate plus 2 per cent ammonium sulphate as a first application followed by a second application of Liberty® plus 2 per cent ammonium sulphate were the most effective against ARG.

Liberty® at the higher label rate (3L/ha) plus 2 per cent ammonium sulphate followed by a second application 14 days later at 3L/ha was effective in reducing ARG density.

Liberty® at the lowest label rate of 2L/ha plus 2 per cent ammonium sulphate followed by a second application 14 days later did not provide adequate control of ARG in the Hart or Hill River trials.

Pot trials demonstrated that humidity following application of Liberty® is very important to glufosinate activity on ARG. When humidity is lower, increasing the photoperiod from one to eight hours was associated with better ARG control. Liberty® was more effective against 2-3 leaf stage ARG than the later growth stages.