Alternative second knock herbicides for broadleaf weeds in fallow – are there other options?
Unfortunately, these approaches have added cost, complexity and scheduling issues to weed management programs but have been required for two main reasons:
To control herbicide-resistant weed populations, that may have been selected by prolonged use of a similar mode of action chemistry; and
Control of weed species or stages that are unsuccessfully controlled with single herbicide applications.
Paraquat has been the key active ingredient used in the second knock situation and can provide effective management of a wide range of grass and broadleaf weeds. However, it is clear we require other options to use in this management window to:
Avoid the more rapid selection of paraquat resistance; and
Provide options that may improve weed control in situations where paraquat efficacy is not adequate.
Since winter 2016, NGA has been screening a range of herbicides, to identify options that have the potential for this usage pattern. The two key broadleaf weeds being targeted are common sowthistle (Sonchus oleraceus) and flaxleaf fleabane (Conyza bonariensis).
Alternative Herbicides for Management of Group A Herbicide-Resistant Barley Grass in Field Pea
Barley grass is a problematic annual weed species in Australia, typically growing in areas with less than 425 mm of rainfall. It is commonly found in crop fields and pastures, on roadside verges and in livestock enclosures. Although valued for animal feed in pastures early in the season, upon maturity the long barbed awns of barley grass seeds irritate livestock and entangle in wool, reducing productivity and product quality. Barley grass can also serve as a host for pathogenic fungi and nematodes in cereal-growing areas.
Windmill Grass: Biology
Windmill grass (WMG) is a short-lived perennial grass species that has been problematic in the northern cropping region of Australia and is now becoming more common in the southern region.
It establishes on roadsides and in summer-fallow, where over-reliance on glyphosate has led to the development of resistance. An understanding of windmill grass biology will help guide management choices to enable successful long-term control.
This factsheet includes findings from recent research by the Weed Science Group at the University of Adelaide.
Feathertop Rhodes Grass: Biology
Already a major weed in the northern cropping region of Australia, Feathertop Rhodes grass (FTR) is now occurring in fields in the southern and western cropping regions. FTR has been favoured by the shift towards reduced tillage. In addition, the heavy reliance on glyphosate that typically accompanies reduced tillage has led to resistance, further increasing the threat of FTR. An understanding of FTR biology will help guide management choices to enable successful long-term control. This factsheet includes findings from recent research by the Weed Science Group at the University of Adelaide.
Statice: Biology, Ecology and IWM Tactics
Statice (Limonium lobatum) is a winter annual dicotyledonous weed of Mediterranean origin that has naturalised inland and along some coastal areas of southern Australia.
This herbaceous weed from the Plumbaginaceae family is often found in areas of low to moderate rainfall on sandy to loamy soils that are calcareous, sodic and of neutral to high pH.
Long-range dispersal is by seed, either through contamination of grain crops, harvest or tillage machinery, or by movement with livestock. Infestations are more common in pastures, roadsides and undisturbed habitats, however recently this weed has invaded cropping areas, particularly where crops are rotated with pasture.
In the absence of effective early control, deep-rooted statice plants can compete with crops for nutrients and moisture, reducing crop growth and yield potential. In dense stands, crop yield losses can be as high as 20 to 30%. Statice can also cause problems at harvest, with green leaf material often discolouring and contaminating grain.
Stewardship First SprayBest Guide
The application of herbicides late in the season to prevent weeds setting seed or to desiccate crops must be carried out with caution and in line with herbicide label recommendations.
It is essential to check if these practices are acceptable to buyers, as in some situations markets have extremely low or even zero tolerance to some pesticide and herbicide residues.
Stewardship for pre-harvest application of herbicides in winter crops
The application of herbicides late in the season to prevent weeds setting seed or to desiccate crops must be carried out with caution and in line with herbicide label recommendations. It is essential to check if these practices are acceptable to buyers, as in some situations markets have extremely low or even zero tolerance to some pesticide and herbicide residues.
Long-term Control and Seedbank Depletion of Annual Ryegrass: Management Strategies
Annual ryegrass is a major winter annual weed of the southern Australian wheat-belt, which naturalised after its introduction as a pasture species.
If not managed effectively, ryegrass can significantly reduce the yield of winter crops. Many populations of ryegrass have developed resistance to selective grass herbicides used in crops, making post-emergent control difficult.
Growers must now plan carefully how to best manage ryegrass populations, and considerations start with crop choices and the associated weed control options available.
A succession of years with multiple and diverse control options used in varying cropping phases is central to successful ryegrass management.
Roly poly, also known as prickly saltwort or tumbleweed (Salsola australis R.Br.), is a native species found throughout Australia with the exception of Tasmania.
The dead plants can break off at ground level, forming the iconic ‘tumbleweeds’ seen in movies. Roly poly, along with a range of other species in the Salsola genus, is a prominent weed of agricultural systems internationally.
Like most summer weed species, roly poly utilises soil moisture and nutrients that would otherwise be available to the following crop. The time taken to clear uncontrolled plants may delay seeding. Livestock will graze the young plants.
However, they will not eat the mature plants and are injured by the prickly leaves. This species has tentatively been linked to oxalate poisoning, but most tests indicate that oxalate levels are insufficient to poison sheep. Levels of oxalates and nitrates in roly poly may increase in the presence of nitrogen fertiliser or legume species.
The dead, mobile tumbleweeds can become a significant fire hazard, particularly when too many plants pile up against fences or buildings.
Note that as a native species, this species is not a problem in areas of native vegetation, and plays a valuable role in revegetation of disturbed sites.
This weed is found throughout Australia, with the exception of Tasmania. The origin of this species is unknown, but it may be native to the Kimberly, Pilbara and desert regions of Western Australia.
There are twelve species of Boerhavia in Australia, but B. coccinea is the most common in disturbed areas like agricultural fields or roadsides.
It is a common summer weed species, and like most summer weeds it depletes soil moisture and nutrients, reducing the yield potential of the subsequent crop.
This weed also acts as a green bridge for crop pests and disease, including scab disease, Melon viruses, Xylella fastidiosa disease of grapes and plague locusts. It can be a beneficial and highly palatable pasture species. Further updates are available here.
Button grass can be a pain in the butt!
Button grass (Dactyloctenium radulans) sounds kind of cute, but that’s not always the case! It’s a native species found throughout Australia and is a common summer weed species.
Like most summer grass weeds it depletes soil moisture and nutrients, reducing the yield potential of the subsequent crop. Summer weeds also act as a green bridge for crop pests and disease.
The rapid emergence and growth of button grass after rainfall makes it important for the Australian plague locust.
It can be a valuable pasture species in arid areas, although overgrazing of button grass (green or dry plants) in stockyards can result in nitrate-nitrite toxicity in sheep and cattle.
Further, toxicity from prussic acid can result in the field when hungry stock are exposed to lush growth. However, dry plants are rarely toxic in the field. Button grass is difficult to control, as the stressed, dusty plants are poorly responsive to herbicides.
Herbicide resistant wild radish: take back control
Herbicide resistance in wild radish is developing fast!
Effective management to control wild radish populations is imperative to protect your productivity; prevent herbicide resistance and avoid its spread.
Implement an effectively timed 2-spray herbicide strategy
Wild radish size when treated greatly affects herbicide efficacy; always spray small plants
Using multiple mode-of-action chemical groups will delay onset of herbicide resistances
Prevent wild radish seed set. Deplete soil seed banks to wipe out herbicide resistant populations and impede the development of resistance