Barley grass continues to be challenge

The event was hosted by the Western Beef Association and the Department of Primary Industries and Regional Development (DPIRD).Catherine Borger, a DPIRD research scientist, spoke about the life and seed cycles of two types of nearly identical barley grass varieties - Hordeum leporinium and H. glaucum.

"They've got more variation than other grasses which makes them a whole lot harder to manage," Dr Borger said.

One of the most challenging traits of barley grass is that it has a staggered emergence through autumn and winter, and can still be germinating by September.

Therefore, it's difficult to address during pre-seeding spraying, or using non-selective herbicides.

If buried under the soil, barley grass seeds can last up to three years before it germinates, and so, can take years of management before the problem is controlled.

Dr Borger advised against feeding barley grass to livestock, as it has been proven to show carcase, hide and wool damage.

"I get that coming out of summer when there's not much else to eat and barley grass has come up first, it can be tempting to use it as a pasture feed," she said.

"There's a lot of economic modelling that shows that is a loss in the long term."

Dr Borger said these varieties of barley grass were showing small signs of resistance, more so on the east coast.

Group 2 herbicides, specifically Imidazolinones or IMIs, were showing signs of being most at risk of resistance.

"We are lucky in WA that we have no resistance to glyphosate or paraquat, in the Eastern States they are starting to get that resistance," Dr Borger said.

"It's nothing to panic about, but we do want to manage those herbicides."

In order to emerge and grow, barley grass needs to go through hot weather then cold weather, and rain.

Hot weather is guaranteed in WA's climate, but temperatures dropping cold enough for seed emergence can be difficult, especially if seeds are buried under the soil.

Instead of germinating earlier in the season, barley grass may germinate well into winter, and this is what can lead to a staggered germination.

A trial was completed at Kellerberrin between 2019-2021 which looked at management.

The pasture treatments included an early application of a selective herbicide at the two to four-leaf stage, and late season control via spray topping or slashing.

In 2019, the trial started with volunteer regenerating wheat and clover pasture, which saw an application of Targa at the two to four-leaf stage in July, at a rate of 250 millilitres per hectare.

In September, Paraquat was spray topped at 400ml/ha.

At the end of the year, the pasture was grazed.

The results from this year showed Targa to be successful, killing all barley grass, and low growing season rainfall prevented re-emergence later in the year.

Spray topping alone did not prevent seed set and contributed to lower pasture biomass.

When combined with Targa early on, the growth of wheat and clover improved.

In 2020, wheat was sown, the plots were split and underwent applications of Treflan, and a combination of both Treflan and Sakura.

The wheat crop with both Treflan and Sakura was less dense than the plot with the Treflan application, with only 11 barley grass plants per square metre compared to 82 plants/m2.

In 2021, volunteer wheat and clover pastures grew again, with a June application of 45 grams/ha of Raptor.

While the density of barley grass was low following 2020, the applications of Treflan and Sakura made no difference to seed production in 2021.

Early application of Raptor did not control all of the barley grass, and the wetter season contributed to late seed emergence.

In September it was slashed, which removed the barley grass panicles and prevented seed set.

In this year, pasture biomass was high, unaffected by the weed management methods, however was slightly lower after slashing.

The Kellerberrin trial shows that one single control option has variable results due to seasonal variability, and that while early chemical control cannot remove all barley grass, it can increase pasture biomass later in the season.

A combination of both early and late season control, along with grazing, can prevent barley grass seed set.