Change in tactic against barley grass in rotations

The Mallee Sustainable Farming group held a research update at Karoonda this month and guest speaker, the University of Adelaide's Chris Preston, addressed herbicide resistance and in particular the status of resistance in barley grass.

Dr Preston said a few trials in the Mallee produced good news for croppers, showing that rotation management was a key tool that growers had control over.

"It is mostly good news," he said. "We are seeing a range of barley grass resistance to particular chemical groups so it is important to draw on other tools to stop it from becoming a serious issue in cropping and pasture rotations.

"There is a small amount of glyphosate resistance but overall, the news is mostly positive and most products are still effective on barley grass."

Dr Preston said barley grass issues in rotations that were heavy in cereals and pastures, were well documented.

He said barley grass simply "loved" it and the lack of control for growers, during the cereal phase of crops in particular, posed the greatest threat for paddocks becoming overrun with it.

"It can bloom out of control easily and working out when it is best to activate barley grass control is crucial," he said.

A recent trial in a wheat and pasture rotation at Lameroo found in barley grass issues across all crops.

"We also found that in paddocks that have been continuously cropped for about 10 years, there was a shift in barley grass germination," Dr Preston said.

It found barley grass plants were emerging a lot later in the cropping phase.

"It used to be killed off with a knockdown earlier in the year and now we are finding that in continuous cropping, it is not coming out until after first rain - it is waiting until after sowing," Dr Preston said.

The grass actually requires a fair bit of dark days and cold nights to emerge well.

Dr Preston said that caused a pretty big issue because of the difficulty to manage dormant barley grass.

"Not getting it with a knockdown chemical and in the cereal phase, means there are not a lot of choices after that," he said.

"Growers rely heavily on Clearfield crops and if that tool is pushed too far, we could end up with herbicide resistance.

"We do not have a lot of resistance yet but it is out there - we need to package that and look at other options for management."

EARLY competition in paddocks that are battling barley grass has proven to help reduce barley grass plants producing seed.

Multiple trials, including at Lameroo, have shown this can be a simple change that has a great advantage for growers.

Researcher Chris Preston said early barley grass plants can shoot away and produce tillers that set a lot of seed.

"In pasture management, this needs to be looked at closely," he said.

"The most damaging barley grass is what comes up early - it will be the biggest plant produce the most amount of seed heads than anything else.

"A bit of early competition by scratching in barley at Lameroo helped to reduce the number of barley grass plants."

Dr Preston said one of the best weapons for growers to use against the weed was ensuring crops were as competitive as possible against barley grass, and for as long as possible.

These gaps in crop competition were strongly linked to barley grass becoming an issue and in pastures, extra management in grazing and foot traffic can also help.

Working to ensure crops grow bigger, earlier, was also an effective tool. Dr Preston said that would always ensure better competition against weeds.

In the pre-emergent herbicide space, he cautioned growers against spending a lot of money on new products that simply suppress it, making it shorter in the crop.