Investing in early summer weed control can pay dividends

Author: Sharon Watt | Date: 01 Dec 2015

Rob Sonogan Southern Panel

Grain growers in the southern cropping region are advised to turn their attention to early control of summer weeds which rob valuable moisture and nutrients from soils into which next year’s crops will be sown.

Grains Research and Development Corporation (GRDC) Southern Regional Panel member and Swan Hill-based agronomist, Rob Sonogan, encourages growers to get on top of any summer weeds early to increase the effectiveness of weed management measures and prevent weeds from being a larger problem later.

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

In many environments, the contribution of the extra nitrogen made available to the next crop from control of summer weeds is just as (and sometimes more) important than the contribution from extra water stored.

An adequate supply of nitrogen is critical to capture the benefits of high levels of stored soil water and reciprocally, a high water supply is required to capture the benefits of nitrogen fertiliser.

GRDC-supported trials in southern New South Wales have illustrated that for every millimetre of moisture lost via summer weed growth, a further 0.64 kilograms of nitrogen/hectare was made unavailable to the following crop.

Mr Sonogan said uncontrolled weeds not only reduced soil moisture and nitrogen, but could also lead to equipment blockages that impeded efficient sowing operations.

“Controlling summer weeds can assist growers in sowing their crops on time and can also minimise disease and insect issues that can occur when a ‘green bridge’ of weeds and volunteer cereals is allowed to survive over summer.”

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, 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

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


Sharon Watt, Porter Novelli, 0409 675100

Region South