Ryegrass is on the attack

Words: Neil Waddingham, Bayer New Zealand  

Ryegrass is on the attack and time isn’t on our side. 

High ryegrass populations in the spring reduce yield and may increase the risk of herbicide resistance developing.

All indicators show that the arable industry needs to combat ryegrass now, or its impact on both cereal and ryegrass seed crops will rapidly get worse.

Over the past three seasons sales of Sakura have grown strongly based on the impact of ryegrass. 

Sakura is recognised as the premier herbicide for the control of ryegrass and in autumn 2025 Bayer expects further growth. 

Applied post-planting but pre-emergence, Sakura controls ryegrass before it can compete with the crop minimizing the detrimental impact ryegrass has on crop yield. 

Because Sakura controls ryegrass early in its lifecycle when it is very small it is much easier to control. 

Sakura also controls a wide range of other grass weeds including vulpia hair grass and annual poa.

Ryegrass is quickly developing resistance to many herbicides in New Zealand, especially the Group 1 and 2 herbicides, and even glyphosate (Group 9). 

But fortunately, this isn’t the case for Sakura (Group 15 herbicide). 

It was against the background of the increasing impact of ryegrass, and ryegrass herbicide resistance, that Bayer, along with its partners PGG Wrightson Retail and PGG Wrightson Seeds, invited Peter Boutsalis to NZ in July 2024. 

He is the director of Adelaide-based Plant Science Consulting, with extensive expertise in ryegrass management and an in-depth knowledge of Sakura and Roundup UltraMAX, key defence tools against ryegrass.

Boutsalis spoke to many agronomists and farmers while in NZ, with those fortunate to be able to attend his meetings universally saying how informative they were. 

But not everyone could attend. 

Therefore, to ensure his expertise is available to all, Bayer videoed his Ashburton presentation and this can be viewed via the Bayer website. 

The video contains a wealth of information about ryegrass control and why it is such a challenge; the mechanisms of herbicide resistance; why some herbicide groups are more at risk of developing resistance than others; the value of pre-emergence herbicides and how to get the best from Sakura and Roundup UltraMAX. 

So, let’s tease out some key messages from Peter Boutsalis’ video. 

Ryegrass is a difficult weed to control due to two main factors. 

First, it is a prolific seeder and second, it must outcross with another ryegrass plant to set seed. 

Outcrossing means that any resistance genetics the plant possess is rapidly spread. Controlling ryegrass is a numbers game. 

The starting point is usually a high weed seed population and because herbicides don’t give 100 per cent control multiple control measures are required to reduce competition. 

Starting with the pre-emergence application of Sakura, followed by effective in crop herbicides and ending with effective harvest seed hygiene.

But it is a numbers game in a second way. 

A very small percentage of ryegrass seeds naturally have the genetic coding to be resistant to herbicides with the likelihood for this to be against Group 1 and 2 herbicides rather than pre-emergence herbicides. 

So, the target must be to expose as few ryegrass plants to Group 1 and 2 herbicides in the spring as possible. 

The key ways to do this are to keep ryegrass seed on the soil surface where a large percentage of seeds naturally die; and apply Sakura to further significantly reduce the ryegrass population. And of course, early ryegrass removal by Sakura reduces crop competition and protects yield.

These points, along with others, are expanded upon in Peter Boutsalis’ video, available online at the Bayer website.