Moree trial confirms new option for resistant wild oats

Ashley, who has worked with Landmark in the region for four years, said more than half of the wheat production area contained grass weed populations that were on the verge of herbicide resistance.

“There is a lot of resistance to Group A herbicides. They only work effectively in about 20 per cent of the area,’’ Ashley said.

He said farmers were running out of herbicide options for wild oats (black oats) and some Group B herbicides were becoming less effective against phalaris. Herbicide tolerant wheat and barley crops are increasing the use of this herbicide group.

Resistant annual ryegrass is also becoming more prevalent following previous floods.

“The grass and resistance issues in the south are gradually creeping north,’’ Ashley said.

In the trial, Ashley targeted wild oats in a 100 per cent Group A herbicide resistant paddock comprising grey clay soils on a property east of Moree where wild oat numbers were high.

“The paddock had been sown to cereals for a while. The grower has 10,000 acres (4000 hectares) of wheat and wild oats are in every paddock. Other farmers have similar issues,’’ Ashley said.

He said growers had traditionally used Group A herbicides followed up with spraytopping in problem areas.

There has been increased sales of Atlantis® OD and Hussar® OD post-emergent herbicides for wild oats this year. These are proving effective, but are adding to the pressure on Group B chemistry.

With the widening registration of the pre-emergent herbicide, Sakura® 850 WG, to include wild oat and great brome suppression, Ashley decided to include the Group K herbicide in this year’s trial.

Containing the active ingredient pyroxasulfone, Sakura also controls annual ryegrass, barley grass, silver grass, annual phalaris and toad rush in wheat (not durum wheat) and triticale crops.

It is a highly concentrated granule from Bayer and has a low use rate of 118 g/ha.

The trial comprised strip treatments of tri-allate and triasulfuron applied with and without Sakura, while wetter also was included, with all mixes demonstrating good compatibility.

Following the break to the season, the treatments were incorporated with a conventional tyne and harrow seeding system and a further 25 mm of rain was received at the end of the first week in June before the rainfall later stopped.

Ashley said he was most impressed with the strip that included the Sakura herbicide.

“It was the pick of the treatments. The weed seeds at depth were controlled by the tri-allate and the Sakura picked up the surface germinators.’’

“The (wild oat) population was so high that in the strips without Sakura, the surface germinators were not controlled.

“The grower was very happy with Sakura and it will be used in their program next year, not so much with triasulfuron though – so there is not an over-reliance on Group B (chemistry).

“It is a significant investment at around $55/ha (tri-allate plus Sakura) before factoring in post-emergent applications. Growers used to get away with spending $40/ha all up, but as we see more Group A and B resistance, there is no choice. And if we are having to deal with resistant weeds in wheat and barley, they will also become a problem with chickpeas.’’

As part of the trial, Ashley also applied Atlantis OD in a compatible mix with Velocity® broadleaf post-emergent herbicide, Folicur® fungicide and a spray adjuvant over a section of the paddock with minimal crop effects.

“You could see a direct line in the paddock where the Atlantis was applied,’’ he said.

“Last year black oats were waving their heads across the whole block. This year there is not one – and that’s due to Atlantis.’’

Ashley said applying Sakura and tri-allate and then coming back with a Group B herbicide like Atlantis with Velocity, Folicur and a spray adjuvant would be an ideal strategy.

“The grower will also include fallow and a summer crop to help really drive down the (wild oat) numbers before going back into wheat.’’

“Weed seed management is non-existent here at the moment, but it also will happen,’’ he said.

Bayer Territory Sales Manager Scott Ariell said with Atlantis OD applications on the rise in recent years, Sakura now provided an important chemical rotation option for growers, thereby also helping to extend the life of other existing herbicides, including the use of clethodim and haloxyfop in chickpeas.