Harvest systems combined to crush weed-seed resistance
GroundCover™ Issue: 113 | Author: Melissa Williams
Barry Gray, of South Kukerin, is one of many southern wheatbelt grain growers adopting narrow windrow burning to get on top of problem weeds.
This harvest-weed-seed-control (HWSC) tactic can reduce future weed populations by preventing inputs to the weed seedbank and it reduces reliance on herbicides.
Barry, who farms with his wife Dianne and son Scott, has annual ryegrass (Lolium rigidum) infestations right across his 2000-hectare property, wild radish (Raphanus raphanistrum) covering 60 to 70 per cent of the farm and brome grass (Bromus diandrus) on 10 per cent of the property – and spreading.
Annual ryegrass testing indicates resistance is developing to Group A and B herbicides, limiting the family’s weed-kill options.
Barry says destroying weed seeds at harvest using narrow windrows that are burned the next autumn is a logical and necessary step to reducing long-term weed burdens.
“It is fortunate our main problem weed species retain a high proportion of seed on upright stems and tillers at crop maturity,” he says.
“By cutting the weeds off low with the harvester, their seeds are collected, processed, deposited in narrow windrows in chaff and then destroyed by burning.
“Windrow burning and crop rotations are now our main weed-control weapons and give us flexibility with pre and post-emergent herbicides.”
Barry says he and Scott tried using chaff carts as a HWSC measure for several years, but found they could achieve a more effective burn and weed-seed kill with a narrow windrow system.
They have modified their conventional harvester – a New Holland CX8080 – to place the weed seeds at the top of the windrow so that they can get higher levels of weed-seed control when the windrow is then burned or baled.
The spinners on the harvester have been reversed and these direct chaff towards heavy-duty PVC tubes (300 millimetres in diameter) fitted to the area adjacent to the spinners.
A flap hangs behind the sieves and guides all material into the spinners.
“The chaff is blown down the tubes, hits a piece of carpet between the tube outlets and is deposited on top of the straw windrow, which is about one metre wide,” Barry says.
“This creates a defined separation of chaff and straw, which is vital because the weed-seed-bearing chaff is then in the hottest part of the fire when we burn the stubble rows in autumn.
“Windrows burn well – even after rain – because they are sitting above the cut stubble and there is plenty of air movement and fuel to achieve a hot burn and seed kill.”
Barry says because crops are cut low at harvest, it is easier to keep the fire in the windrow and maintain some protection on the ground between the windrows.
He says this system also maximises the chaff and seeds included in the windrow if the fraction is baled – creating a product with high nutrition that is cheap and plentiful.
Barry says that by using a narrow windrow burning system, the family is now achieving 100 per cent kill of weed seeds that enter the header and total weed reduction across the farm is about 40 per cent better than their experience with chaff carts.
“I estimate our annual ryegrass burden is being halved year-on-year and we are getting good results for wild radish,” he says.
“But I think we are missing some of the brome grass because it sheds its seeds early.”
A new tactic for problem weed patches, especially brome grass, has been a pre-harvest swath (mostly in barley paddocks) to capture seeds before shedding.
Barry says as a result of using HWSC, about one-third of the family’s cereal crops were sown this year with no pre-emergent herbicides for annual ryegrass and half of the farm was not sprayed with any herbicides for wild radish control.
“Our crop yields are better because there are less weeds and we are saving money on herbicides,” he says.
A potential downside is that narrow windrow burning can lead to nutrient loss for subsequent crops, but Barry says the weed control benefits far outweigh any increased fertiliser costs.
He says his biggest concern about HWSC is that it might lead to selection for prostrate growing and early-shedding annual ryegrass to avoid the header front.
“That is why we will continue to use tactical swathing, depending on the season,” he says.
“In the big picture, windrow burning is a low-cost HWSC method and it allows us to sow early into paddocks with low weed burdens.”
Barry estimates that over the past decade, with good integrated weed management strategies, the family has doubled grain production for any given amount of annual rainfall.
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The Gray family’s HWSC methods are outlined in more detail in a GRDC Albany Port Zone Regional Cropping Solutions Network (RCSN) case study booklet, The effectiveness of on-farm methods of weed seed collection at harvest time, available at: www.grdc.com.au/CaseStudy-WeedSeedHarvest-Albany
WeedSmart information hub: www.weedsmart.org.au
GRDC Project Code UWA00124, UWA00146