Australia - Further trifluralin resistant ryegrass confirmed

Grain growers with a heavy reliance on trifluralin for ryegrass management are urged to check their emerging crops in coming weeks for ryegrass resistance.
The reminder from the Australia Department of Agriculture and Food comes after another paddock was found with trifluralin resistant ryegrass in the Northern Agricultural Region.

The paddock was detected as part of the Profitable Crop Sequencing project on a property participating in the Farm Focus Paddock initiative.

Geraldton research officer Wayne Parker said the discovery confirmed research by the Australian Herbicide Resistance Initiative, which has found ryegrass developing resistance to trifluralin to be widespread across the wheatbelt.

In South Australia, trifluralin resistance is widespread and has effectively limited the use of the herbicide in cropping rotations in many areas of that state.

Mr Parker said it highlighted the importance of integrated weed management to minimise the risk of ryegrass developing herbicide resistance.

“A canola phase provides an opportunity for a number of both non-herbicide and herbicide weed management options in order to reduce ryegrass numbers,” he said.

“Pre-harvest swathing and burning windrows also help to reduce the risk. Using a triazine tolerant canola also allows for an alternative herbicide group to be used on the paddock, after wheat crops.”

The department is continuing to test samples from 184 Farm Focus Paddocks on 66 participating properties across the wheatbelt.

“Recent analysis of ryegrass samples from the paddocks involved in the project provided some disappointing results,” Mr Parker said.

“Of the 109 paddocks tested for resistance to date only two still have full activity to the major in-crop herbicide groups A, B, C and D.

“The results provide a warning to growers not to become overly dependent on individual herbicides and to incorporate break crops and other integrated weed management strategies into their cropping programs.”