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Return fire on weed seeds this harvest

Controlling weed seeds at harvest is now considered the number one strategy for prolonging the life of herbicides being threatened by resistant weed populations.

Michael Walsh, Australian Herbicide Resistance Initiative (AHRI) says harvest weed seed control plays an important supporting role to other strategies that focus on early season weed control.

“If there is one message we want to deliver, it is to control weed seeds at harvest – whether that is using the Harrington Seed Destructor (HSD) or a chaff cart behind your header, baling harvest residues, or narrow windrow burning, the key is to capture and destroy seeds from weeds,” Dr Walsh said.

Research supported by the Grains Research and Development Corporation (GRDC) shows seedbanks of annual weeds can be rapidly depleted when harvest weed seed control systems are used to capture/destroy weed seeds at harvest.

“Our weed control efforts are aimed at driving these seedbanks towards zero,” Dr Walsh said.

“Harvest weed seed control systems play an important role in that they are the last opportunity during the cropping season to attack weeds by preventing seedbank inputs.

“The key is: control the seedbank to control the weed.”

Dr Walsh says annual weeds such as ryegrass, wild radish, brome grass and wild oats have adapted to cropping systems, growing to similar heights as cereals and maturing at the same time as annual crops.

“For this reason, some growers may be sceptical about how much seed is captured at harvest but AHRI research shows a very high percentage of total weed seed production is retained on plants at a height that ensures collection during the harvest operation.

“However, the best time to target these weed species is at the start of harvest as weed seed shedding occurs over the harvest period reducing the amount of seed that can be collected and subsequently destroyed.”

He says recent research shows that at the start of harvest high proportions of weed seeds are retained at least 15 centimetres above the soil surface for annual ryegrass (88pc); wild radish, (99pc); brome grass, (73pc); and wild oats, (85pc). By harvesting at this height these weed seeds are captured by the header, and can be dealt with from there.

He urges growers and agronomists across Australia to move from the existing global industry paradigm of controlling weed seedlings to also consider harvest weed seed control.

Harvest weed seed control is the key strategy of the industry-led, WeedSmart initiative which advocates 10 ways Australian farmers can fight herbicide resistance.

WeedSmart brings together industry organisations including GRDC, research providers and major crop protection companies to deliver the message that herbicide resistance is a difficult but not insurmountable problem – but changes need to occur on-farm.

Click here for 10 ways Australian farmers can fight herbicide resistance.

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