Mr Fleet was one of the speakers at last week's Grains Research and Development Corporation update, held in Adelaide.

He is involved with a GRDC-funded project looking at emerging weeds in cropping systems.

"We did a grower survey, comparing the most intrusive weeds now, compared with five years ago," he said.

"Barley grass has become the third most difficult weed Eyre Peninsula farmers are facing. In the Upper North it's the fourth biggest problem. "In other areas it wasn't in the top five, but it was in the top 10 and it's increasing from its position five years ago."

One reason for the growing incidence of barley grass could be the trend towards earlier sowing and dry sowing, reducing the opportunity for a pre-sowing weed kill.

Some barley grass populations collected from the upper EP needed cold stratification; or chilling exposure; to germinate.

This requirement meant a germination was not happening after summer or early autumn rains.

The later dormancy in the barley grass meant it was coming up in crop, so there were few control measures.

"The key message is not to hold back on sowing, but pick out problem paddocks and schedule them later in the seeding program," Mr Fleet said.

"That way you're still seeding your farm at the optimal time, but those problem paddocks are being left until last."

Mr Fleet also looked at the effectiveness of different herbicide options on barley grass in wheat.

"Sakura is a new pre-emergent herbicide that really stood out in trials," he said.

"It was really good for barley grass control and offered consistent results across all sites.

"But it is a premium ryegrass product, so price could be an issue."

Mr Fleet said if it was applied following a pasture or break-crop phase, and used to run down the barley grass seed bank, the cost could perhaps be justified as a lower rate could be used.

Sakura is expected to be available for the 2011 cropping season.

The trials showed a mix of metribuzin, diuron and Logran gave the most consistent control of the lower cost pre-emergent treatments.

For post-emergent treatments, Monza provided higher and more consistent control than Atlantis.

Details: benjamin.fleet@adelaide.edu.au.