Haymaking reduces weed seed carryover

Western Australian graingrowers can reduce weed seed carryover into next year's wheat crops by cutting this year's ryegrass-dominant crops for hay.

Agriculture Western Australia agronomist, Gurjeet Gill, said it is vital for growers to adopt non-chemical methods of reducing ryegrass, such as hay cutting, because the weed's resistance to herbicides is increasing.

"Growers who use the same herbicide continuously are prone to problems, as ryegrass can show resistance after only four applications," Dr Gill said. "Three years ago we estimated 200,000 hectares of ryegrass were resistant to herbicides, but the resistance problem is now spread across 500,000 hectares.

"Cutting crops for hay before the plants shed their seeds can help prevent the resistance problem from reaching uncontrollable levels. Controlling ryegrass is a particular problem in continuous cropping rotations because the weed has a seed carryover rate of 10-20 per cent.

"While it is not cost-effective for growers to stop using herbicides altogether, they can lower the seed bank by capturing weed seeds at harvest and using higher sowing rates.

"In trials funded by the Grains Research and Development Corporation, ryegrass seed was reduced and grain yield lifted when the seeding rate for wheat was increased from 50 to 100 kg/ha. Heavy grazing, spray topping and early manipulation are other viable ways of controlling ryegrass seed-set," Dr Gill said.

Subprogram 3.3.03 Contact: Dr Gurjeet Gill 09 368 3238