Control the seeds to control the weeds

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Dr Michael Widderick

PHOTO: Cox Inall Communications

Driving down the weed seedbank is a grower’s best defence against herbicide-resistance issues, says Dr Michael Widderick, from the Queensland Department of Agriculture, Fisheries and Forestry (DAFF). 

“This requires growers to deal with both the weed seeds already existing in the soil, and stopping additional weed seeds from entering the soil,” he says.

Weed seeds persist longer once they are buried in soil, especially for small-seeded species buried below one or two centimetres, Dr Widderick explains.

“For these species it is better to leave the seed on the soil surface as you know exactly where it is and the environment it’s in,” he says. “But once you have a favourable environment for emergence, you really need to get on to them quickly when they’re small and you know your herbicide treatment is going to be effective.”

Warmer winter – more weeds

With warmer-than-average winter temperatures accelerating the growth of northern wheat crops, it is imperative that growers give top priority to weed control this season to maximise crop productivity and avoid the costly issue of herbicide resistance.

In many areas this will rely on the successful in-crop management of grassy weeds such as wild oats and annual ryegrass – some of the northern region’s most damaging crop weeds, which already harbour widespread resistance to commonly used herbicides.

These grassy weeds are capable of establishing large, persistent seedbanks. If annual weeds are freely allowed to produce seed that enters the seedbank, the inevitable consequence will be an unsustainable cropping system.

Effective weed management in productive cropping systems is therefore reliant on preventing viable seed entering the seedbank.

Target at harvest

Targeting weed seeds at harvest is a pre-emptive strike against problematic annual weeds. It also provides the opportunity to move away from reliance on herbicidal weed control.

Growers are advised to keep a close eye on treated paddocks, and either mechanically remove survivor weeds or mark the patches of concern via GPS to follow up later.

Dr Widderick says there is a perception among some growers that small outbreaks of resistant weeds are not economical to control.

“Growers must keep in mind that some weeds can set between 50 and 1000 seeds annually and, if not controlled, can take over a paddock in less than 10 years,” he says.

“Growers are advised to use an integrated weed management strategy as the most effective method of controlling problem weeds,” Dr Widderick says.

“This can include harvest weed-seed management, as well as crop sequencing, strategic tillage, double-knock treatment of weeds (chemical or mechanical) and the use of pre-emergent herbicides.”

The GRDC is funding numerous herbicide-resistance management programs to tackle these problems in the north. These include an integrated weed management research project and the WeedSmart initiative, which aims to promote the long-term sustainability of herbicide use in Australian agriculture.

More information:

Elise McKinna, Queensland DAFF
07 3087 8576,

The WeedSmart Northern toolbox outlines handy resources for growers to help with the implementation of successful integrated weed management strategies:

Integrated Weed Management Hub:

End of Ground Cover Issue 112 (Northern Edition)

Read the accompanying Ground Cover Supplement: Ground Cover Issue 112 - Managed environment facilities


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GRDC Project Code UQ00062

Region North