Grains Research and Development

Date: 02.12.2014

Managing fleabane

Flaxleaf fleabane (Conyza bonariensis) is the most common of the three fleabane species found in Western Australia. This hard-to-kill weed is rapidly becoming widespread throughout the grain growing regions. Flaxleaf fleabane flourishes in minimum tillage cropping systems, especially in years with good spring rainfall.

Germination usually begins in late August or early September and growth continues after harvest and through summer. Flaxleaf fleabane is a prolific seeder, flowering and setting seed over a long period of time, producing up to 110,000 seeds per plant. These factors, combined with the dispersal of its seed by wind and water over considerable distances, make it a rapidly increasing problem.

In cereal crops, target fleabane seedlings in spring with a late post-emergent application of a suitable broadleaf herbicide.

Fleabane, when mature and under heat or moisture stress, is relatively unresponsive to knock down herbicides, so the best strategy is to control it at the seedling stage during the fallow or in the pasture phase.

When treated young (one month old or less), glyphosate can control susceptible flaxleaf fleabane plants. When mature, however, the weed is very difficult to control with glyphosate, regardless of its resistance status. Treating flaxleaf fleabane after harvest is often ineffective as the plants already have a well developed root system and spray conditions are often far from ideal.

Flaxleaf fleabane can easily establish in and spread from non-cropping areas such as pastures, roadsides and fencelines.

There are no known herbicide-resistant populations of fleabane in WA however there are many documented cases in Australia and overseas of this species being resistant to several herbicide groups.

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Grains Research Updates

Status of key summer fallow weeds in the Riverina an update

GRDC Project Code: UA0134, UCS00200

Author(s): Leslie A. Weston, William Brown, Shamsul Haque and John Broster (Graham Centre for Agricultural Innovation, Charles Sturt University, Wagga Wagga, NSW 2678)

Date: 16.02.2016

• A changing climate in this region has resulted in enhanced significant summer rainfall events in the Riverina, resulting in increased germination and spread of warm season weedy species.
• The use of no-tillage systems for crop production has also resulted in significant residual crop stubble in fallow fields, which can result in retention of soil moisture throughout warm summer months, also facilitating weed growth.
• Many weeds germinate effectively on the warm and moist soil surface, or at shallow soil depths, without significant prior soil coverage in fallow fields.
• The reduction in use of grazing livestock in crop paddocks to remove summer fallow weeds has resulted in the increased need for use of herbicides for summer weed management.
• The timed use of selective or non-selective post-emergent herbicides and integrated weed management options can reduce the prevalence of summer fallow weeds in subsequent years.
• Reducing weed seedbanks is critical to effective control in subsequent years.
• Fleabane, witchgrass, windmill grass, wild melons and Feathertop Rhodes grass are important summer fallow weeds encountered across southern Australia. more

Grains Media Releases

Driving down the fleabane seedbank

GRDC Project Code: ICN00021; ICN00016; UQ00062

Date: 03.08.2015

Zero till farming and wind-blown seed dispersal, coupled with glyphosate resistance has seen fleabane develop as one of the major broadleaf weeds of northern cropping systems. Effective management of fleabane will require a combination of good agronomy; non-herbicide tactics (e.g. crop competition) and strategic use of herbicides. more

Grains Research Updates

Farming systems strategies to manage fleabane and feathertop Rhodes grass

GRDC Project Code: NGA00003, DA00137, UQ00055, UQ00062

Author(s): Richard Daniel, Northern Grower Alliance

Date: 31.07.2015

1. Glyphosate resistant and tolerant weeds are a major threat to our reduced tillage cropping systems
2. Although residual herbicides will limit re-cropping options and will not provide complete control, they are a key part of successful management
3. Double-knock herbicide strategies (sequential application of two different weed control tactics) are useful tools but the herbicide choices and optimal timings will vary by weed species
4. Incorporate other weed management tactics e.g. crop competition to assist herbicide control
5. Cultivation may need to be considered as a salvage option to avoid seed bank replenishment
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Grains Research Updates

Pre-emergent herbicides part of the solution but much still to learn

GRDC Project Code: NGA00003

Author(s): Richard Daniel and Anthony Mitchell, Northern Grower Alliance

Date: 24.07.2015

1. The use of a disc planter for incorporation by sowing (IBS) of residual herbicides resulted in significantly reduced wheat emergence for all four herbicides evaluated
2. The disc planter ‘set-up’ actually increased the risk of crop damage
3. These results reinforce the need to only use narrow point tynes when using residual herbicides with IBS recommendations
4. Residual herbicides are important tools for the effective and economic management of key summer fallow weeds
5. Use of residual herbicides in fallow may suit operations with access to optical sprayers
6. Individual paddock rotations may need to change to enable use of residual chemistry in preceding fallows or in-crop
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