NSW growers urged to be proactive about weed control
Author: Toni Somes | Date: 28 Oct 2016
Warren-based agronomist Penny Heuston said on-going wet weather, particularly in southern and central areas had made it difficult for growers to apply pre-emergent or in-crop herbicides, with many opting to leave weed control until harvest.
But Ms Heuston, who is also the Grains Research and Development Corporation (GRDC) northern panel deputy chair, said it was critical growers had an action plan for weed seed control or they risked a blow-out that could cost them for years in yield losses and increased herbicide inputs.
“We have had high and regular rainfall across many areas of the state creating perfect conditions for weed growth with limited opportunity for chemical or mechanical control,” she explained.
“If growers don’t get on top of the problem early and effectively they risk major weed problems that have the potential to impact crop rotation flexibility, as well as yield loss through increased weed competition, putting extra pressure on herbicides.”
Ms Heuston is urging growers to set-up low cost and easily implemented options, like windrow burning or chaff tramlining, before winter crop harvesting starts in earnest. But she said determining the most effective weed control method hinged on knowing weed density and species in paddocks.
“Growers should walk through paddocks and do a visual assessment of weed density, as well as weed type so they know what is out there, in effect a ‘’paddock audit’’ each year. I would also recommend they collect weed seed for herbicide resistance sampling, so we continue to build a picture of what is happening at paddock level.”
Then she said it was a case of taking effective action.
“Windrow burning basically requires growers setting up a chute at the back of the harvester so harvest residue, including weed seeds are left in rows in the paddock for a hot burn later that will kill weed seeds,” Ms Heuston explained.
She said this approach was particularly well suited to pulse and oilseed crops. In contrast in wheat and barley stubbles it may be harder to contain the burn in windrows. However, she said it has been done successfully over a number of years in the central west with some on the ground extension done by the GRDC-funded Grain Orana Alliance (GOA).
“If you maintain stubble over summer to retain moisture and then burn prior to sowing, you will lose organic matter, but with the heightened weed risk this season that may prove the lesser of two evils,” Ms Heuston said.
“But just burning the paddock won’t do as it has to be at a certain temperature for a certain number of seconds to kill weeds. For example it is higher for radish than rye – so 400 degrees for 10 seconds for rye, but 30 seconds for radish.
“Another economical and easy to set up system is chaff tramlining, where weed seed is put on tramlines within the paddock, so in effect no organic matter is leaving the paddock, it has just been redistributed to the high traffic areas, these are the most hostile environments for weed seed germination.
“Alternatively, if growers have a chaff cart this is the season to get it out of the shed. The key message is growers need to take action and there are plenty of guidelines and videos about how to set up different harvest weed seed control (HWSC) options on the GRDC website.”
HWSC is a call to action supported by Director of Weed Research at the University of Sydney, Michael Walsh, whose work in New South Wales is funded by the GRDC.
Dr Walsh said some growers had been skeptical about introducing HWSC, but the potential weed risk this season made it an astute move for those keen to safeguard their cropping enterprises.
“There is some weed seed shedding at maturity, but our research shows a high percentage of total weed seed production is retained on plants at a height that ensures collection during harvesting.
“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.”
Dr Walsh has been integral in developing HWSC processes, and said his research shows regardless of the method (Harrington Seed Destructor, chaff cart behind the header, direct baling harvest residues or narrow windrow burning) they are all similarly effective in capturing and destroying weed seeds.
“We know at the start of harvest high proportions of weed seeds are retained above a low harvest height (15cm) for annual ryegrass (88 per cent), wild radish (99 per cent), brome grass (73 per cent), and wild oats (85 per cent) and by harvesting at this height these weed seeds are captured by the header and can be dealt with from there.
“HWSC in NSW winter crops is the obvious starting point as seed retention is highest then. The national weeds survey found approximately 13 per cent of NSW and Queensland growers are already diverting the weed bearing chaff fraction onto permanent wheel tracks in controlled traffic farming (CTF) systems. Growers already practicing CTF can do this at low cost.
“Narrow windrow burning in chickpea crops is another easy place to make a start with HWSC. Seed retention was excellent in chickpea crops and it is simple to burn chickpea windrows without burning the entire paddock. Burning cereal windrows is also possible, but more challenging given the higher levels of dry matter.”
For more information about HWSC practices in the northern check out the Beginner's guide to harvest weed seed control
Or to watch HWSC in action check out the video GCTV15: Harvest Weed Seed Control
Penny Heuston, GRDC northern panel deputy chair
0428 474 845
Toni Somes, Senior Consultant, Cox Inall Communications
GRDC Project Code UWA00146, UWA00171, US00084