Ryegrass, once the diet of countless sheep throughout the Western Australian wheatbelt, has developed an appetite of its own, eating into wheat yields.

With sheep numbers declining, herbicide resistance increasing and no-till systems sparing ryegrass the ‘harrowing’ experience, researchers are seeking weed control alternatives.

Supported by the Grains Research and Development Corporation, the Western Australia Department of Agriculture’s Abul Hashem believes sowing may hold the key.

“The uniform distribution of wheat seeds via cross sowing can minimise competition between wheat plants, while increasing their competition against ryegrass weeds, which flourish between rows in traditional seeding regimes,” he said.

During cross seeding, half the seed is deposited in one direction and the balance in a second pass, at a right angle. Fertiliser is applied equally in each direction.

Working with Catherine Borger and Glen Riethmuller, Dr Hashem experimented with the technique at Merredin in 1997, before adding trifluralin at seeding in subsequent trials at Merredin (1999, 2000, 2003) and Mullewa (2000, 2003).

The cross seeding pattern worked, with ryegrass biomass falling 14-32 per cent in Merredin and almost 30 per cent in Mullewa.

“Cross seeding limited ryegrass growth and ultimately dropped seed production by an average of 37 per cent, compared with conventional seeding,” Dr Hashem said.

“Trifluralin was also effective, with ryegrass seed production falling 61 per cent with its incorporation, regardless of the seeding technique used.

“When combining cross-seeding and trifluralin, ryegrass seed production was lowered by as much as 85 per cent.”

Reduced competition from ryegrass also increased wheat yield, although Dr Hashem emphasised the long-term benefits of ryegrass control were more important than the seasonal benefits.

The second seeding pass costs an additional $25 per hectare and extra grain yield of 150 kg per hectare is needed to break even, although yield increases of up to 500 kg/ha are possible by cross seeding. 

The benefit cost ratio of cross seeding, using trifluralin and seeding at 150 kg per hectare, was 2.22.

Cross-seeding wheat with trifluralin lifted wheat yield 10-23 per cent on the back of an 8-30 per cent crop biomass increase.

In a Kellerberrin paddock suffering from high resistant ryegrass numbers, this technique lifted yield by 500 kg/ha. “Cross seeding can be added to a grower’s weed control options as a non-chemical alternative, or used in association with trifluralin,” Dr Hashem concluded.

A group of farmers in Esperance also experimented with the technique in 2001, a relatively dry year, with their results replicating Dr Hashem’s.

Several oaten hay producers in Western Australia’s southern wheatbelt have adopted cross seeding because it allows them to sow at rates of 150 – 170 kg/ha, which can’t be delivered in a single pass. This helps produce softer hay, which is more palatable to stock.