Spray weeds early and save

Author: Sarah Jeffrey | Date: 07 Dec 2015

Image of Sharon O'Keeffe

The early and effective control of summer weeds will top the priority list for growers with the onset of the summer storm season.

Early warm weather and storm events have meant conditions are ideal for a flush of summer weeds and the Grains Research and Development Corporation (GRDC) is urging growers to control summer fallow weeds early to maximise effectiveness, preserve precious stored soil moisture and protect the yield potential of future crops.

GRDC grower services manager north, Sharon O’Keeffe said early weed control had the potential to deliver significant benefits in production.

Research supported by the GRDC has quantified the value of efficient stored soil moisture to northern farming systems with trials showing that even an extra 20 millimetres of stored soil moisture can be worth an extra 0.5 tonnes a hectare in additional yield.

 “In summer, the difference between effective and ineffective weed control is only a matter of days, not weeks,” she said.

“Weeds can make or break efficient water storage during the fallow. As a general rule, if summer weeds are allowed to establish in the fallow, they will start extracting water from depth – more than 100mm depth – within about 12 days of establishment. That’s water that could be used to grow a following crop.”

She said it was important that growers had spray equipment at the ready, used robust rates and adhered to best management spray application recommendations on water rate, environmental conditions, droplet size and boom height.

 “Control rates can be very effective if plants are sprayed when they are small but leaving them too long can be a costly failure, requiring additional control measures and risking the development of herbicide resistance on farm. The most expensive spray is a failed spray,” she said.

“As most growers would be aware, there are some key factors that impact on the efficacy of summer herbicide applications including adjuvant selection which is critical to the performance of most active ingredients.

“Adjuvants may improve herbicide efficacy by reducing evaporation, increasing droplet survival on leaf surfaces and increasing penetration of herbicide active ingredients into the plant.

“Of course efficacy is also significantly impacted by temperature and humidity, travel and wind speed, droplet size and viscosity of spraying liquid so it’s really important from a cost/benefit and sustainability perspective to adhere to best management recommendations on spray equipment and conditions.”

New South Wales Department of Primary Industries (NSW DPI) technical specialist weeds Tony Cook said growers looking to maximise soil moisture storage in fallow consider applying a pre-emergent herbicide initially to control weeds in the germination stage.

 “The first flush of weeds is usually the worst and applying a pre-emergent herbicide can be an effective early knock. This can be later followed up with a knockdown herbicide application as necessary.

“Applying a pre-emergent early in the summer fallow also gives some herbicides time to break down so plant-back restrictions don’t become an issue next winter.”

Pre-emergent herbicides are becoming increasingly used in integrated weed management programs as advisors and growers look to alternative modes of action for hard-to-kill weeds and an increasing range of weeds with resistance to post-emergent herbicides.

For many, the challenge in using pre-emergent herbicides lies in ensuring they work consistently with minimal crop damage. This requires an understanding of both the label directions and the chemical properties of pre-emergent herbicides and how these interact with the soil and environment.

For more information on managing weed seedlings and developing an integrated weed management strategy is available from the GRDC’s Integrated Weed Management Hub.

Contact Details 

For Interviews

Sharon O’Keeffe
GRDC Manager Grower Services, North
0409 279 328

Bernadette York, media officer NSW DPI
0427 773 785


Sarah Jeffrey, Cox Inall Communications
0418 152859

Region North