Don't take rain check on summer weed control

Author: Natalie Lee | Date: 27 Oct 2014

Research has demonstrated the profitability of controlling summer weeds early, which increases soil water and nutrients available to the next season’s crops, boosting their yields and grain quality.

Caption: Andrew Storrie, Agronomo, inspects flaxleaf fleabane in a recently harvested paddock.

Agronomo principal Andrew Storrie said significant recent rainfall in the Western Australian grainbelt would encourage the germination of summer weeds.

Mr Storrie has helped update Grains Research and Development Corporation (GRDC) resources that can guide growers on pre-harvest herbicide application to control weeds in winter crops, and post-harvest control of summer weeds.

The updated GRDC Pre-Harvest Herbicide Use Fact Sheet provides information about stewardship for in-crop herbicide use late in the season, and the GRDC Summer Fallow Weed Management reference manual demonstrates how growers can reap a high return on investment from managing summer weeds.

Mr Storrie said controlling germinating summer weeds in-crop, where possible, would give growers a head start on summer fallow management and lead to more water being retained in the soil, as well as extra nitrogen being available to crops in the next season.

“If these weeds are left uncontrolled until after harvest, they will be bigger and harder to control,” he said.

Mr Storrie said the GRDC Pre-Harvest Herbicide Use Fact Sheet contained information about product registrations for pre-harvest weed control and desiccation.

Caption: The GRDC RCSN summer weed trial site at Moorine Rock during the 2013 cropping season, with the unsprayed plot in foreground.

“It’s important that product labels are followed and withholding periods are adhered to for all herbicides, to minimise the risk of maximum residue limits (MRLs) being breached,” he said.

Mr Storrie said the Summer Fallow Weed Management manual included grower and researcher case studies and research data.

“It provides essential information on the value of stored water; the effects of summer weeds on nitrogen; other weed effects on following crops; use of herbicides in the fallow; and effective spray application,” he said.

“A big advantage from controlling summer weeds is that the retained soil moisture will give growers a better chance of sowing crops on time next year, delivering yield, weed and risk management benefits.”

Mr Storrie said water stored below 30cm in the soil profile had a high conversion rate to grain produced.

“The two WA case studies in the manual show that control of summer fallow weeds can increase crop yields by up to 800 kilograms per hectare in a drier winter,” he said.

Mr Storrie said using herbicides to control fallow weeds had been shown to be more effective than grazing or cultivation at killing the weeds and maintaining stubble cover.

Meanwhile, GRDC Regional Cropping Solutions Network (RCSN) research in WA’s eastern grainbelt will this season measure the impact of different timings of summer weed control.

“In 2012, the project found a significant moisture conservation response in the root zone (to a depth of 40cm) of plots sprayed in early summer, compared with unsprayed plots,” RCSN coordinator Julianne Hill said.

“The response ranged from about 9mm of soil stored moisture at Doodlakine up to about 60mm at Southern Cross.

“Spraying out summer weeds at harvest, as opposed to leaving it until later in summer, also improved early crop vigour in the following year’s crop, and has been shown in most cases to reduce the incidence of root diseases.”

The Kwinana East RCSN has established soil moisture capacitance and neutron probes during 2014 which will give a real time measure of soil moisture from the different timings of summer weed control at each of the trial sites in the eastern grainbelt.

The GRDC Pre-Harvest Herbicide Use Fact Sheet is available at

The Summer Fallow Weed Management manual is available for viewing and downloading via the GRDC website at or hard copies can be ordered through the GRDC’s Ground Cover Direct, free phone 1800 11 00 44 or email

Information is also available at the GRDC Integrated Weed Management Hub and the WeedSmart website


Contact Details 

For Interviews

Andrew Storrie, Agronomo

0428 423 577

Julianne Hill, GRDC RCSN

0447 261 607


Natalie Lee, Cox Inall Communications

08 9864 2034, 0427 189 827

GRDC Project Code ICN00012, KE12/13-3of4

Region West