Summer weeds seek to rob recent rain gains

Author: Tristan Price | Date: 22 Jan 2015

Rob Sonogan, Southern Panel

Key points:

  • Recent rain in Southern Cropping Region means summer weeds for grain growers
  • Weed management should address weeds while they’re smaller and more vulnerable
  • Growers should be mindful of seasonal, localised and general spraying conditions

After recent rains across Australia’s Southern Cropping Region, grain growers are being urged to get on top of summer weeds that are out to steal valuable moisture and nutrients from their soil.

Grains Research and Development Corporation (GRDC) southern panel member and Swan Hill-based agronomist, Rob Sonogan, said the recent rains in many parts of southern New South Wales, South Australia, Victoria and Tasmania could be enough to initiate germination in summer weeds.

With that in mind, growers should get on top of summer weeds early, while they are small, to increase the effectiveness of weed management measures and prevent them from being a larger problem later.

“Even small summer weeds can rapidly deplete soil moisture and also tie up mineralised soil nutrients,” Mr Sonogan said.

“The amount of recent rain that will be saved for the coming season’s crops will depend on the soil type, the surface cover and of course how much rain fell. If no follow-up rains occur over summer, then recent rain events of less than 30mm will generally not leave any soil moisture in the profile.

“Soil moisture that finds its way to depth and is stored there is extremely beneficial to the coming crop. Water Use Efficiency (WUE) or the ability of a crop to convert available water into grain is greatly increased in most seasons when sourced from depth.

“The longer the topsoil remains moist after a rain event, the greater the mineralisation of nutrients occurs; this rain event has been followed-up by unusually cool summer conditions which will have maximised this beneficial process. The mineralised nitrogen, if saved by controlling summer weeds, can add to the profits of the coming season.” 

While spraying summer weeds as soon as possible can offer a significant advantage for the following crop, growers should also be mindful of seasonal and continuing issues around spraying.

“There are precautions that all growers must observe when spraying and others that might be specific to their area, like the Chemical Control Areas within North West Victoria where no Ester sprays can be used, as well as the ever present issue of spray drift and inversion conditions that must be avoided,” Mr Sonogan said.

“Growers should also be aware of new areas sown with summer crops that are highly susceptible to chemicals, such as to cotton, and extreme care must be taken to avoid damage to these if spraying summer weeds in certain districts.”

For more information on managing summer weeds in the Southern Cropping region, see the GRDC Summer Fallow Weed Management Manual at

More information on weed management can be found at the GRDC Integrated Weed Management Hub,, or WeedSmart,


For Interviews

Rob Sonogan, GRDC Southern Panel
0407 359 982


Tristan Price, Porter Novelli
(03) 9289 9517

Caption: GRDC Southern Panel member, Rob Sonogan, says now is an ideal time for grain growers in Australia’s Southern Cropping Region to address summer weeds after recent rainfall events. 

GRDC Project Code ICN00012

Region South, North