Controlling weed seeds at harvest is key to overcoming herbicide resistance

Controlling weed seeds at harvest is emerging as the key to managing the rising herbicide resistance levels putting Australia’s no till farming system at risk.

Peter Newman, Australian Herbicide Resistance Initiative (AHRI) communications leader told the recent Grains Research and Development Corporation (GRDC) Update at Narromine, NSW that herbicides are not the answer to herbicide resistance.

“Removing weed seeds at harvest is currently our greatest non-herbicide weed control tool in Australian grain cropping,” Mr Newman said.

“This practice is now widely adopted in the form of narrow windrow burning, chaff cart, bale direct, diverting weed seeds onto permanent tramlines, and now the Harrington Seed Destructor (HSD) developed with assistance from the GRDC.

“All of these tools are equally effective at removing weed seeds, averaging 55 per cent removal of annual ryegrass seeds according to GRDC-funded AHRI research.

“They all differ in their cost and the amount of residue that they remove from the paddock.”

Mr Newman told central west NSW growers and advisers data from a selection of 24 focus paddocks where the growers are cropping dominant with no livestock in the farming system showed positive trends over 12 years.

“Growers in the focus paddocks using harvest weed seed control reduced ryegrass levels from 183 ryegrass plants per square metre in 2001 to close to zero in 2008 and they have maintained these levels ever since, demonstrating the benefits of removing weed seeds at harvest.

“It is quite remarkable that growers have been so successful at eroding annual ryegrass seed banks of paddocks, while maintaining a cropping intensity of 88pc.”

Mr Newman says many of the original messages about managing herbicide resistance in 1990s were built around the concept of phase farming, however research shows it is possible to crop at high intensity while eroding the weed seed bank despite high levels of herbicide resistance.

“Growers who have had the most success at managing ryegrass populations are those who have practiced harvest weed seed control in the form of narrow windrow burning or by towing a chaff cart,” he said.

“Harvest weed seed control does not fix a system that is broken but can be the key to making a system work.”