Decide who is calling the shots

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Photo of the integrated Harrington Seed Destructor

Harvest weed seed destruction using tools such as the integrated Harrington Seed Destrutor is critical to reducing weed seedbanks.

PHOTO: Evan Collis

Fast facts

  • Don't let weeds dictate your farming system
  • Decide what farming system you want and then add enough weed control to make it work
  • A diverse approach to weed control can lead to a near-zero seedbank

The only true, long-term solution to managing herbicide-resistant weeds is to have a very low (near-zero) weed seedbank. It is flexible and profitable – and it slows resistance evolution


The 'big six' tools for very low seedbanks.

  1. Double-knock to look after glyphosate – it is a precious resource
  2. Mix, rotate and double-knock selective herbicides.
  3. Compete – maximise crop competition with weeds to minimise crop losses from weeds and minimise weed seed set. Narrow row spacing, east–west sowing, competitive cultivars, high seed rates.
  4. Stop weed seed set – crop topping
  5. Harvest weed seed control – every paddock, every year.
  6. Phase farming – livestock are not popular with all growers, but well-grazed pasture in the rotation is still a great tool for mixed growers.

Who is calling the shots on your farm: the grower or the weeds? If weeds are dictating crop choice, crop area or time of sowing, the chances are they are costing a lot of money. It is grain growers with very low weed seedbanks who can call the shots and make their farming flexible and profitable.

When Ray Harrington sold all of his sheep in 1996 in some of Australia’s best sheep country, he knew he had to be aggressive with weed management or ryegrass would beat him. Ray wanted to be in control of his farm and crop it wall-to-wall. He had seen growers in the Western Australian wheatbelt move to continuous cropping and develop big problems with herbicide-resistant ryegrass.

He had also witnessed those same grain growers have a win by adopting harvest weed seed control (HWSC) in the form of the chaff cart – and he knew he had to do something similar.

Choose the farming system

Ray farms with his nephew, Tim, in a successful continuous cropping rotation near Darkan in the south-west of WA. Ray and Tim have been destroying weeds as they exit the harvester on the farm for several years: four years with tow-behind Harrington Seed Destructors (HSDs) and the past three years with the new iHSD (integrated unit). However, there is more to their success story than just this machinery innovation.

Every grower is different, but everyone should be able to choose the farming system to meet their triple bottom line of ‘people, planet and profit’. Rather than have weeds dictate the farming system, it is better for the grower to decide how they want to farm and then add enough weed control to make this farming system work. The question to ask is: “If I wasn’t worried about herbicide-resistant weeds, how would I like to farm?”

Diversity

The trick is to use a combination of mechanical, cultural and chemical weed control rather than just relying on the herbicide drum. Ray and Tim’s aim is to never let a weed set seed. They use a diverse range of tools selected from ‘the big six’ (see box at right) in a ‘take no prisoners’ approach:

  • mix and rotate and double-knock herbicides at robust rates (chemical);
  • crop rotation (cultural);
  • 22.5-centimetre (nine-inch) row spacing with robust seeding rates, achieving a high level of crop competition (cultural);
  • swathing, sometimes including spraying under the swathe of canola – in 2016 they swathed every hectare of crop [canola, wheat and barley] (mechanical and chemical); and
  • integrated Harrington Seed Destructor (mechanical).

This approach works. At Darkan, where Tim and Ray farm, it is cold and wet. The country features non-wetting soil that causes ryegrass to germinate until late in the growing season. However, in spring, there is little ryegrass to be seen in-crop. The ryegrass that can be found is late-germinating, competing with a large crop, and the little seed it produces is destined to be swathed and destroyed.

Near-zero seedbank

Graphic showing that growers using harvest weed seed control in addition to other tactics have reduced their ryegrass seedbank to near zero

Figure 1 Growers using harvest weed seed control (HWSC) in addition to other tactics have reduced their ryegrass seedbank to near zero.

SOURCE: Peter Newman

Over the past 16 years, the GRDC has funded the monitoring of 26 focus paddocks, first by the Department of Agriculture and Food, WA, and now through the GRDC-supported Australian Herbicide Resistance Initiative (AHRI). Using an aggressive approach to weed management, 12 growers have successfully reduced ryegrass to near-zero (Figure 1). As with Ray, the growers practising HWSC are using other tools as well, but HWSC is the tool that shifts them from a low weed seedbank to a near-zero seedbank.

How low is ‘near-zero’? Even a few weeds per square metre is considered too many. Growers with very low seedbanks have up to 50 metres between weeds in their crops. Low weed seedbank cropping takes a shift in mindset to get on the very low seedbank path and several years to achieve. Importantly, it is less reliant on future herbicide discoveries.

Ray and Tim are confident that they can keep their entire farm in crop if they choose to do so, without being beaten by weeds. A diverse system is harder than just applying herbicide and takes considerable effort and design, but the proof is in the pudding. Growers taking this diverse approach are winning and are confident about their cropping future.

More information:

Peter Newman,
0427 984 010,
Australian Herbicide Resistance Initiative

GRDC Project Code UWA00171

Region West