Ground Cover Supplement : GC Supplement - Weeds
4 GROUNDCOVER Issue 128 | May – June 2017 | GRDC GROUNDCOVERTM SUPPLEMENT: WEEDS NORTHERN REGION Multiple tactics needed for the north RESIDUALS AND STRATEGIC TILLAGE As growers are forced to move away from reliance on knockdown herbicides in no-till systems, the range of chemicals being used and the methods of applying them are widening. “The main change we are seeing is a weed spectrum increasingly dominated by glyphosate-tolerant or glyphosate-resistant species and an increasing reliance on residual herbicides and double-knock,” Northern Grower Alliance (NGA) chief executive officer Richard Daniel says. Mr Daniel says weed control is being researched by NGA through its Grower Solutions projects. The work has found that while double-knock treatments can be much more effective than single applications, they come at considerable cost and can still have variable levels of control. “For instance, glyphosate mixed with 2,4-D followed by paraquat is still the most consistent option for fallow fleabane management, but will frequently only provide 70 to 80 per cent control,” Mr Daniel says. “Double-knocks can be expensive in ter ms of cost of herbicide, labour and spray rig capacity, particularly when the level of weed control is still incomplete. So there are situations where growers should consider alternative strategies including tactical use of tillage or residual herbicides.” Mr Daniel says strategic tillage can be a useful tool, particularly for surface- ger minating weeds such as feathertop Rhodes grass. Its most likely fit in northern farming systems comes after low-stubble crops such as chickpeas. “Feathertop Rhodes grass emergence, for example, can be reduced by up By Liz Wells n The ability to grow summer and winter cereals, legumes and oilseeds gives some growers in the northern region the chance to make rotations their greatest ally in weed management, but the region also throws up circumstances that make the suppression of weeds far more complex than this. Wildly variable rainfall, diverse soil types and an ever-expanding number of invasive species require northern growers to have a range of weed management options ready to use when conditions prevent rotations from working effectively. Several of these options are being evaluated in GRDC-funded projects and their impact on far ming systems is being taken into account as growers look for ways to minimise weed infestations without adding further pressure through herbicide resistance. The projects are also looking into the phenology of weeds in the hope of finding periods of weakness in plants’ life cycles when they can be destroyed or prevented from germinating. FAST FACTS n Growers are turning to double-knock and residual herbicides in response to glyphosate resistance. n Strategic tillage can be a useful control for emerging weeds such as fleabane and feathertop Rhodes grass. n Controlling weeds in non-crop areas such as fencelines will reduce the spread of weeds into paddocks. GROWER MESSAGE Non-herbicide treatments, including use of rotations, are the best way for growers in the northern region to control weeds. Strategic tillage is also a useful tool and, in the future, growers can expect to see innovative engineering solutions becoming available. PHOTO:TONYCOOK Feathertop Rhodes grass invading a sorghum crop from a fenceline on Queensland’s central Darling Downs.
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