On the frontline of IWM

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Key points

  • Mark Pearce is eager to use his revamped chaff cart this season to manage herbicide-resistant weeds: the weed burden has increased in its two-year absence
  • An early harvest and the right rotation are also part of an integrated approach to herbicide-resistant weed management 

Mark Pearce has been forced to replace chemical herbicides with a combination of tools and tactics to counter herbicide resistance

Image of grower Mark Pearce

Tarin Rock grower Mark Pearce has implemented a range of alternative practices to herbicide use.

PHOTO: Evan Collis

In the 12 years since Western Australian mixed farmers Mark and Lisa Pearce began farming at Tarin Rock, about 300 kilometres inland from both Perth and Albany, they have tried many measures to deal with the property’s herbicide-resistant weeds.


Farm manager: Mark Pearce
Farm size: 2500 hectares, 1100ha leased
Location: Tarin Rock, Western Australia
(35 kilometres west of Lake Grace)
Enterprises: cropping and first-cross South African Meat Merino-Merino sheep
Average rainfall: 320 millimetres
Soil types: sandy gravel to medium loam
Ideal crop rotation: two break crops
between cereals
Crop program (2015): wheat (700ha), barley (870ha), canola (750ha), lupins (80ha), oats (80ha) and clover (450ha)

“When we bought the property it had been continually cropped for a long time,” Mark recalls. “We did some testing and found no chemicals were working.”

To date, the best practices to tackle the widespread ryegrass and wild radish resistance to Group A, Group B and triazine herbicides have been improved rotations and the addition of a chaff cart, something that Mark is keen to see working again this harvest.

The cart is a tag-along machine that gathers chaff from the header – including problem weed seeds – and dumps it into easy-to-graze or burn piles. The set-up now includes a conveyor belt, added for the 2012 harvest, which makes the cart easier to use and piles more straw to achieve a hotter burn.

However, an electrical fault in 2013 that started a fire, which burnt the cart and 50 hectares, put the equipment out of action for the next two harvests. A replacement cart last year proved problematic.

“The chaff cart is integral,” Mark says. “And after two years without it you can definitely see the weed burden building up. Radish, brome grass and ryegrass numbers are more noticeable.”

As an alternative, Mark tried to windrow behind the header. “But we found it hard to get a hot enough burn and the weeds tend to show up in the windrows for the next few years.”

The Pearces’ approach to integrated weed management also includes harvesting early.

“The whole district tries to harvest as fast as possible. On our farm, we aim to harvest the dirty paddocks before the weed seeds start to shed. Otherwise they will be below the height of the header and won’t be picked up and put in the chaff cart.”

Part of the plan to speed up harvest and get in before weeds start to shed seed has been the purchase of a new header, which Mark says will reduce his harvest time by two weeks.

Rotations role

The other crucial component to managing herbicide resistance is rotations: “In cereal crops I just assume that no chemical is going to kill the grass weeds, so rotation plays an important role. And the best rotation seems to be using two break crops between cereals, such as one or two pastures or legumes, followed by canola.”

Increased barley plantings – including imidazolinone-tolerant barley – have also helped.

The Pearces increased barley plantings after reducing the amount of oats planted after some low-yielding dry seasons and poor prices. Mark says the move has had a positive impact on weed management as well as profits. “We get better weed control with barley than we did with oats and a better margin.”

Mark now feels oats are better suited to higher-rainfall areas: “They can perform well, but are high maintenance.”

And despite barley’s propensity to shed heads in high winds – losses can be as high as one tonne/ha – Mark is keen to persist with the cereal.

“Even if we lose a lot of heads it still yields better than wheat (and oats). A lot of R&D is being done on the issue and it still pays well despite the losses.”

The farm’s sheep – first-cross South African Meat Merino-Merino sheep – are also happy to graze on what the wind blows off: “It is a good example of where a mixed farm works well for us. The sheep are a good fit and a good risk-management tool.”

Mark says sheep fit well with the family’s philosophy of improving the land with pastures and legumes – land that is unsuitable for cropping because of surface rock.

Mark says managing this mix of cropping and grazing landscape is helped considerably by having access to local knowledge through his local grower group – the Lakes Information and Farming Technology (LIFT) group – and the GRDC’s Regional Cropping Solutions Networks.

In particular he is keen to draw on other growers’ knowledge and experience to gradually introduce controlled-traffic farming (CTF).

The Pearces are starting the process of creating permanent wheel tracks so that crop zones and traffic lanes are separated to address compaction in lighter soils.

Using two-centimetre guidance, Mark is working to 12-metre widths, which will require some machinery to be modified. He also plans to invest in precision-agriculture technology, but says it is a long-term program that will be implemented step by step: “Yield monitoring will be the start and we’ll see how we go from there,” he says.

“It’s been good to talk this through with other growers. It seemed daunting, but the group has helped me to think about it as a long-term program so the cost of these changes can be spread over a few years.”

Formed in 2008, the LIFT group’s interests include soil health (such as non-wetting soils), frost, climate variability and farming systems adaption, and mixed farming.

“Having a grower group means we can more easily encourage researchers to come and visit, ensuring more local trials,” Mark says.

“Most of us are a lot happier to ask questions of researchers and each other in our small group. It’s proved great for bouncing ideas about.”

International trips, such as the GRDC-sponsored WA Grains Group visit to China in 2013, also helped shape an understanding of what export markets and consumers value: “The trip was a real eye-opener, especially the amount of time and effort they are putting into R&D. Their research facilities are huge.”

Back home, Mark is just as enthusiastic about his own R&D, in particular the need to make headway again with the chaff cart in his battle with herbicide-resistant weeds and with CTF, which he sees as fundamental to his cropping future.

More information:

Mark Pearce,

0428 959 106


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