Managing ryegrass in winter cereals

PRODUCTION ADVICE - MAY 2021 - AGRONOMY

By John Fowler
Extension Agronomist
P: 03 5881 9933 | M: 0427 079 138 | E: john.fowler@lls.nsw.gov.au 

Annual ryegrass is one of the most troublesome weeds of winter crops.  It usually finds a way to get around growers attempts to manage it in their cropping programs, especially if they rely solely on herbicides for control.

There have been two local projects looking at ryegrass management over the past six years.  The first was funded by Catchment Action NSW and the second by the Grains Research & Development Corporation (GRDC). This article will highlight some of the findings from these projects and comment on principles of ryegrass weed management.

Project ^#1: Catchment Action

This project initially compared the efficacy of pre-emergent herbicides with post-emergent.  It confirmed that:

• Pre-emergent herbicides are usually more effective than post-emergent
• The more expensive pre-emergent herbicides (e.g. Sakura ®, Boxer Gold®) are more effective than trifluralin.
• Resistance to post-emergent herbicides (and Group B pre-emergent herbicides) is common
• Using both pre- and pos-emergent herbicides usually gives the best ryegrass weed control
• A post-harvest weed seed control technique further reduces ryegrass populations in the following crop

The following table shows how the various treatments in 2016 impacted ryegrass seed survival.  It indicates the effect the treatments had at reducing the ryegrass populations the following autumn.

(The letters indicate statistical significance.  Any treatments that have the same letters are not considered statistically different from each other.  For example, the first three treatments all have the letter ‘d’, so are not statically different from one another, however treatment 1 is statistically different from treatment 4 as it does not have a ‘d’ alongside it.)

The autumn burn of the stubble was the method used to reduce post-harvest seeds in this trial.  It was not very effective when it was used alone (i.e. treatment 6) but was very useful when used in combination with a rigorous herbicide regime. Other effective harvest weed seed control systems that don’t require burning include chaff lining (low cost), chaff decks (increased cost) and seed destructors (high cost).

Project ^#2: GRDC Integrated Weed management project

This project was done in association with the Central Murray Ag Group based in the Bunnaloo area.  One of the demonstrations examined the impact of seeding rate on weed establishment and seed set.  The results are summarised below.

The crop had a pre-emergent herbicide application of trifluralin plus triallate (i.e. Avadex® Xtra).  The higher seeding rates did not seem to have any impact on the germination of rye grass, but they did provide extra competition during the growing period that led to less weed seed set.

WeedSmart Big 6

Both these local projects gave results that agree with the ‘WeedSmart Big 6’ message on weed management. While not all six principles were demonstrated in these projects, those that were (i.e. No’s 3, 5 & 6 in the following table) reinforced the principles of effective weed management.

The WeedSmart Big 6:

1. Rotate crops and pastures
2. Double knock to preserve glyphosate
3. Mix and rotate herbicides
4. Stop weed set (crop topping)
5. Provide crop competition
6. Use harvest weed seed control

Ryegrass needs to be actively managed to prevent it causing major crop losses.  Relying on herbicides alone will not prove effective in the long run.  They need to be complemented with other agronomic practices to prevent ryegrass blowouts in future crops.