Growers are being urged to try to control weed seeds during harvest as a key strategy for prolonging the effectiveness of certain herbicides, which is being threatened by resistant weed populations.
Dr Michael Walsh from the Australian Herbicide Resistance Initiative (AHRI) says harvest weed seed control plays an important supporting role to subsequent early season weed control.
“If there is one message we want to deliver, it is to control weed seeds at harvest – whether that is by using the Harrington Seed Destructor 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 says.
GRDC-supported research shows seedbanks of annual weeds can be rapidly depleted when harvest weed seed control systems are used to capture and destroy weed seeds.
“Our weed control efforts are aimed at driving these seedbanks towards zero,” Dr Walsh says. “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 high percentage of total weed seed production is retained on plants at a height that ensures collection during harvesting.”
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 (88 per cent), wild radish (99 per cent), brome grass (73 per cent), and wild oats (85 per cent). By harvesting at this height these weed seeds are captured by the header and can be dealt with from there.
Dr Walsh urges growers and agronomists to move from the existing global industry paradigm of controlling weed seedlings to also consider harvest weed seed control.
The effectiveness of on-farm methods of weed seed collection at harvest booklet is available here.