- Harvest weed seed control plays an important role in stopping weed seeds from entering the soil.
- Harvest weed seed control involves collecting, destroying or burning weed seeds that are present at harvest and is particularly effective in problem species such as wild radish and annual ryegrass.
- While extremely successful in Western Australia, harvest weed seed capture and destruction techniques are unlikely to be effective against the 70-plus weed species present in northern paddocks.
- Further research into the effectiveness of various harvest weed seed control techniques in northern farming systems is required.
Harvest weed seed control is shaping up as grain growers’ next line of defence in the on-going battle against herbicide resistance in the northern cropping belt.
Herbicide resistance poses a major threat to the long term viability of the northern grains industry with resistance issues across a multitude of weed species and modes of action.
Its management is a key investment area for the Grains Research and Development Corporation (GRDC) which is funding trial work into the extent of herbicide resistance to weed types and multiple modes of action, the effectiveness of non-herbicide tactics in suppressing weed growth and driving down the weed seed bank and integrated weed management programs.
Addressing growers and advisers at the GRDC Updates earlier this year, Department of Agriculture, Fisheries and Forestry (DAFF) principal research scientist Dr Michael Widderick said while resistance to one mode of action herbicide was extremely common in the north, many cases of multiple or cross resistance was also now occurring particularly in problem weeds like wild oats.
He said driving down the weed seed bank was growers’ best defence against herbicide resistance issues and that there were two primary considerations – dealing with the weed seeds already existing in the soil and stopping additional weed seeds from entering the soil.
“The initial component is really about controlling any new emergences of weeds and not allowing them to set seed,” Dr Widderick said.
“We have some really good tactics for that like the double-knock tactic for key species like fleabane, feathertop Rhodes grass and awnless barnyard grass.
“The second component – stopping weed seed from entering the soil – has fewer control tools available but one of the new approaches is harvest weed seed control.”
Harvest weed seed control was a tactic developed in Western Australia in the wake of escalating issues with herbicide resistance and centres on collecting, destroying or burning weed seeds that are present at harvest and has been particularly effective in problem species such as wild radish and annual ryegrass.
However the wider spectrum of weeds found in the northern region - at least 70 different species with varying seeding traits - means that harvest weed seed capture and destruction techniques are unlikely to be effective against all species present in northern paddocks.
The greatest opportunity for harvest weed seed control lies with species that set seed above a harvesting height (at least 15 cm above ground level) and retain seed through the traditional winter crop harvesting periods.
“We certainly see that there’s a fit for these tactics in the north but we also have a lot of questions over their effectiveness on our particular weed species.
“What we do know is that at harvest time in our summer and winter crops, there are a lot of weed species present that are setting seed.
“What’s currently happening is that these weed seeds are going back into the soil during the harvest process.”
If implemented regularly, the use of one non-herbicide weed seed control tactic every harvest will play a key role in keeping northern cropping land productive and extending the useful life of existing herbicide chemistries.
Control tactics include the use of narrow windrow burning, bale direct, chaff cart and/or the Harrington Seed Destructor.
One of the simplest tactics is narrow windrow burning which is best suited to non-cereal crops such as lupins, canola and field peas and cereal crops yielding less than 3 tonnes per hectare.
The bale direct method involves attaching a square baler to the harvester to collect and bale both the chaff and straw component.
Chaff carts are a relatively inexpensive option for collecting the weed seed bearing chaff while retaining the straw in the field, and the Harrington Seed Destructor crushes the chaff including the weed seeds and returns all chaff and straw to the paddock, maximising the nutrient and soil moisture benefits of these residues.
Trialling the Western Australian approaches to weed seed bank control within the northern farming systems will be the next step for industry, according to Dr Widderick.
“It’s a simple process of seeing what weeds are present, collecting seeds at harvest and destroying them and then assessing weed emergence in the following season with and without those tactics,” he said.
“That will give us a good picture of percentage reduction in certain species.”
One of the quandaries facing industry in terms of effective weed seed control is whether growers are better advised to leave weed seed on the surface or bury it through strategic tillage.
Part of the answer lies with a seed’s potential for persistence - the timeframe weed seeds survive within the soil.
Weed seed will persist for longer once it is buried below 1cm-2cm, particularly for a number of the small seeded varieties present in the north.
“I believe we still have many effective herbicide options despite resistance issues and that it is better to leave the weed seed on the surface,” Dr Widderick said.
“Then you know what you are dealing with, you know where the weed seed is and what environment it is in.
“In those instances, the key is that once you have a favourable season for emergence, control is implemented quickly when weeds are small and herbicides are going to be effective.”
For more information on weed seed control and integrated weed management strategies, visit www.weedsmart.org.au/wp-content/uploads/2013/01/WeedSmart_SustainabilityGuide_V14-Northern_LR.pdf.
Caption: Department of Agriculture, Fisheries and Forestry (DAFF) principal research scientist Dr Michael Widderick emphasised the importance of driving down the weed seed bank for effective herbicide resistance management during a presentation to the GRDC Northern Grains Research Update at Goondwindi earlier this year.
Elise McKinna, DAFF Media & Communication Officer
07 3087 8576
Sarah Jeffrey, Senior Consultant Cox Inall Communications
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