Turning up the heat on summer weeds

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Dr Jason Emms, GRDC Manager Weeds

GRDC is committed to invest in research, development and extension to create enduring profitability for Australian grain growers, part of which is reducing the yield gap and optimising input costs. Reducing the impact of summer weeds on summer crops and subsequent winter crops is an important step towards achieving that. In fallow, summer weeds are the enemy of soil moisture conservation. Research as part of GRDC’s National Water Use Efficiency (WUE) Initiative demonstrates that controlling summer weeds is the biggest single contributor to improving WUE. As rainfall patterns become more variable growers are increasingly reliant on stored soil moisture from the summer fallow, making this one of our most precious resources.

Summer weeds also consume soil nitrogen and provide a green bridge that can harbour pests and diseases. In summer crops, weeds can have a substantial impact on crop yields. Effective and cost-efficient management of the summer weed burden is vital to maintain a profitable cropping system.

Repeat Offenders

While the type of summer crop and fallow weeds will vary depending on the season, the region and its cropping systems, there are some repeat offenders. In the northern region the most important weeds continue to be fleabane, awnless barnyard grass, common sowthistle, feathertop Rhodes grass and windmill grass. Melons, caltrop and fleabane are important in both the western and southern regions. However, some traditionally northern weeds such as feathertop Rhodes grass are emerging as problem summer weeds across southern and western Australia.

Several weeds present in summer, such as common sowthistle, are able to germinate and reproduce throughout the year. These weeds may germinate multiple times in the year and set seed over several months. We need to develop integrated strategies with robust and varied tactics to manage these weeds throughout the cropping cycle.


GRDC supports research into the biology and ecology of important summer weeds to help us better understand each weed and to identify its weaknesses. Many of the weeds discussed in this GroundCover™ Supplement are prolific seeders with relatively short-lived seedbanks that are favoured by no-till systems. These provide opportunities for rigorous management programs to dramatically run down seedbanks in a relatively short period of time.

Many important summer weeds, such as fleabane and feathertop Rhodes grass, have a natural tolerance to glyphosate even as small plants. As glyphosate has taken over from tillage as the most common method of fallow weed control the incidence of glyphosate-resistant summer weeds has increased. While the double-knock is an important tactic, we need to be increasingly inventive to stay on top of changes to resistance status. With the northern region starting to see more cases of herbicide resistance in summer weeds, a broader range of integrated weed management tactics such as competitive summer crops are increasingly important. We also need to consider the effects of using herbicides during summer and take extra precautions to minimise their impact on off-target crops and products.

This GroundCover™ Supplement presents information on:

Against a backdrop of increasing herbicide resistance and declining terms of trade, GRDC’s determination to develop more innovative and integrated weed management solutions is stronger than ever. We will continue to support our growers to implement more sustainable and cost-effective options to manage summer weeds.

More information

Dr Jason Emms
0439 549 950