Herbicide ticks ryegrass resistant box

By Shannon Beattie


A new cinmethylin herbicide from BASF called Luximax is the first unique mode of action in a generation and as such has been given its own group.

The herbicide controls multiple resistant ryegrass, is tolerated by wheat, likely by P450 enzymes, however applying it directly to seeds will reduce wheat survival.

Cinmethylin is an old herbicide which has never been registered previously in Australia, with research showing it will be very useful in ryegrass management in the future.

Australian Herbicide Resistance Initiative (AHRI) researcher Roberto Busi said back in the day it made sense to simply rotate between herbicide groups.

"We have found ryegrass that was resistant to one herbicide for example Sakura (pyroxasulfone) was also cross resistant to other herbicides such as Boxer Gold and Avadex through metabolism-based resistance," Dr Busi said.

"Now we can no longer assume that a new herbicide will kill a resistant population, even if it's from a different group of herbicides, so we now need to test new herbicides across our multiple resistant ryegrass."

During the 2018 harvest, Dr Busi offered free herbicide resistance testing and he received 130 annual ryegrass samples.

He screened these samples with the common pre-emergent herbicides trifluralin, prosulfocarb (Arcade) and pyroxasulfone (Sakura), as well as the new product Cinmethylin (Luximax).

The results showed that Cinmethylin performed very well compared to the other pre-emergent herbicides and trifluralin was the worst performer due to resistance to this herbicide.

A couple of years ago with new research about the potential for cross resistance between some of the pre-emergent herbicides, AHRI created boxes.

The boxes act as a guide to help growers choose the best mix, rotate and double knock strategy between herbicides with activity on ryegrass.

Pre-emergent herbicides with known metabolism-based cross resistance have been grouped together, although they have been slightly separated as it is possible to mix and rotate between these products, but there is increased risk of resistance if growers do so.

For example, Dr Busi said the Sakura and Avadex mix had featured in many plot trials and often resulted in excellent ryegrass control.

"Using this mix is better than using either of these herbicides alone, but we want you to be aware that there is a risk of cross resistance between these products," he said.

"Based on my research, Luximax gets its own box because at this stage there is no known and consistent cross resistance to any of the other pre-emergent herbicides."

Dr Busi said it was very challenging for companies to take new herbicides to market these days because the new products didn't just need to control ryegrass, they needed to control ryegrass that was already resistant to multiple herbicides.

"This research gives growers and agronomists some much needed information about a new herbicide before it comes to market helping them to make the best decisions on how to use this new product," he said.