Slarke family, Lake Grace WA

The Slarke family at Lake Grace, in WA’s southern wheatbelt, is transforming how they farm and manage weeds on their 8800 ha aggregation.

Since taking over the farm in 1988, Kim and Michelle Slarke have always appreciated the arm’s length involvement of Kim’s parents, Lindsay and Annie, and Kim’s sister, Michelle, particularly around harvest time.

With a healthy succession plan being implemented, it is exciting for Kim and Michelle to support the sons as the fifth generation to farm in the area. Jamie and his wife Felicity, and Harrison and his partner Tuscany, are driving the business forward with new ideas in farming practices and technology. The Slarkes also employ a full-time worker, Chaddy and other seasonal workers.

The family began minimum till farming and planting with knife points about 30 years ago and implemented autosteer on east-west AB lines where possible in 2008. They have been control-traffic farming since 2019, when they were able to get the last of the machinery onto 3 m wheel centres, all to establish a sustainable farming practice that will see them well into the future.

The Slarkes own two cropping blocks and lease a neighbour’s property that lies between their other two blocks, located about 8 km east of Lake Grace. The soil types range from Lakebank and Mallee soils to ironstone gravels. To address the variability in pH and nutrient status of the different soil types, the Slarkes have mapped their paddocks and used variable rate technology to apply lime and fertiliser.

Resistance test shock

In 1993, soon after taking over the family farm, Kim noticed that some annual ryegrass had grown through applications of sulfonylureas (SU) herbicides. They collected seed for their first herbicide resistance test in 1994 – in the very early days of herbicide resistance testing in Australia. The results showed the ryegrass population was resistant to the Group 2 [B] SU herbicides, was mostly resistant to Group 1 [A] fops (e.g. Hoegrass), and that they only had a few shots left before the Group 1 [A] dims would no longer be effective. From then on, Kim decided to treat all the ryegrass on the farm as if it was resistant to SU, fop and dim chemistry.

“Initially, we were shocked by the herbicide resistance test results,” says Kim. “It was a real wake-up call, but the shock has generated a deep respect for the need to protect each mode of action in our program. As new products become available, we add them to the program. The potential for resistance is always on our minds – how can we protect this chemistry and keep it effective long-term?”

Annual ryegrass is the main weed on the farm and dictates most of their rotation and herbicide use planning. Ryegrass tends to increase on the lighter to medium clay soils and is generally less of a problem on the heavier soil types. Other weeds include volunteer crop plants, capeweed, wild turnip, and small areas of barley grass and brome grass.

The Slarke family implement all of the WeedSmart Big 6 tactics in their integrated weed management program to minimise the impact of herbicide resistance on their farming business.

Making the crop rotation work for weed control

Since 2018, break crops have replaced the 25 per cent of the rotation that had previously been sown pasture for the sheep. A typical rotation now is a legume or canola crop followed by two to three cereal crops, then back to canola or perhaps oaten hay, depending on the weed burden in each block.

“Our operation is now 100 per cent cropping with a typical rotation including barley, wheat, canola, lupins, field peas, faba beans and some oaten hay,” says Kim. “The clover and medic pastures we grew in our crop rotation for the sheep played an important role in building soil health and fertility. We want to maintain that in the new system with grain legumes and the canola, with additional synthetic fertilisers.”

The legume options for the area are field peas and faba beans, which grow better on heavier soil types, and the lupins on the lighter country. They budget for a 5 to 10 per cent yield sacrifice in the legumes because of the variation in soil type within a block. The Slarkes find that the management efficiencies they achieve with block planting outweigh these yield reductions in small sections within a block.

While staying with the rotation that works well with block planting, they will respond to an unforeseen blowout in weed numbers to include a crop that might give more opportunities to capture those weeds. For example, in 2023, they planted the canola block to a TruFlex Roundup-ready hybrid canola, giving them multiple options to control weeds germinating during the season and drive down a growing weed seed bank.

The break crops enable the use of different pre-emergent herbicides at seeding and the option to crop-top and stop seed set in later germinations. The fixed nitrogen input and disease break also contribute to better cereal crops.

The Slarkes use Roundup-ready canola hybrids in their break crop phase and have grown imi-tolerant (Clearfield) barley for over a decade. They started including imi-barley in their rotation to address the increasing numbers of barley grass and brome grass, which are now all but eradicated from their paddocks.

Being conscious of the risk of accelerating glyphosate resistance in ryegrass particularly, the Slarkes try to use alternative knockdown chemistries where they can. For instance, if there is a weed flush before the canola emerges, they use another knockdown, such as paraquat, to control those weeds. At the other end of the season, they use diquat (e.g. Reglone) to desiccate the crop and stop seed set in any weeds that have survived the glyphosate applications in-crop. They also rely on their impact mills at harvest time to destroy any remaining weed seeds.

They are open to crop-topping imi-tolerant feed barley with glyphosate if the weed seed maturity suits the application window. Again, the impact mills play an important role in protecting the herbicide tolerance traits.

In 2022, the Slarkes had an issue with carryover imidazoline that was applied three years previous. Although sufficient plant back time had elapsed, the seasons between had been dry, and some residual herbicide remained in the soil when they planted canola in 2022. The canola was damaged to such a degree that they had to spray it out and reseed the block to imi-tolerant barley. They didn’t use imidazoline that season to ensure all the residual was degraded. In 2023, they planted imi-tolerant canola and applied imidazoline to keep on top of barley grass and brome grass.

Block farming has changed the way they farm

Since selling the last of their sheep in 2018, the Slarkes have implemented a block farming system where blocks of up to 2000 ha are sown to a single crop species. This maximises machinery efficiencies and streamlines operations like chemical applications.

“Our livestock enterprise had been very successful over a long period, but Jamie and Harrison were not particularly interested in continuing to run sheep,” says Kim. “Livestock are time-consuming, and ensuring that animal husbandry and welfare are always prioritised is demanding. We now have additional time and labour resources to direct towards our expanded cropping activities.”

The block farming layout allows the Slarkes to complete major operations like seeding and harvesting without moving machinery back and forth.

The main infrastructure changes have been the removal of fences and lone, stressed trees in favour of protecting the remnant vegetation areas. They have been pleased with how the unfenced shade areas on the edges and within the paddocks are thriving without grazing pressure.

Removing the fence lines has effectively removed one of the farm’s primary sources of weed seeds and herbicide resistance. No longer needing to manage these ‘weed nurseries’ has been a significant benefit of changing to block farming.

Over time, the legacy effect of the old fence lines within the blocks is reducing as Kim has applied multiple in-crop strategies to keep running down the weed seed bank.

“In the first few years, we would patch out some of those fence lines if the weed numbers were high, using a suitable in-crop herbicide or even spraying out the crop along the old fence line if necessary,” he says. “The aim is to pull those weed numbers down until it is impossible to identify the old fence line due to a higher weed burden.”

Multi-faceted crop competition

The Slarkes implement several strategies to promote crop competition, including narrower row spacing, higher seeding rates, east-west sowing, variable rate nutrients and soil amelioration.

“Soil health is the number one driver for our business,” says Kim. “We have done our best to respect our soils and improve soil health so our crops can reach their yield potential for the rainfall received. Nearly thirty years ago, we started addressing the low pH of our soils with lime applications.”

Kim says the benefits of the liming program are clear, and they have also applied gypsum to improve the structure of their heavier clays and reduce the hard-setting traits of these soils.

More recently, they have started using a deep-ripping, rock-crushing machine called a ‘Reefinator’, invented by WA farmer Tim Pannell, to increase soil depth and create a good seed bed in ironstone gravel zones where crops had previously struggled to establish.

The Slarkes have found that it often requires up to five passes over a few years to create 160 to 200 mm of soil depth. These gravelly, ironstone areas usually have some clay present, so the process has been very effective in improving crop germination and productivity of these soils. The Reefinator also thoroughly mixes in previously applied lime and nutrients to support competitive crops in previously low-yielding areas prone to weediness. They have almost completed treating the 10 per cent of their farm that requires ‘reefinating’.

They also use a rock picker to collect surface rocks in their paddocks. Removing the rocks and sticks allows them to safely harvest at can height, ensuring maximum weed seed collection.

Over 15 years ago, when the Slarkes started auto-steer farming, they implemented east-west sowing across their farm wherever the topography allowed. This maximises crop competition by using the crop to shade the inter-row space.

Kim says they were convinced by the significant research by GRDC and other groups showing that east-west planting, particularly in cereals, is beneficial for competition against weeds.

“About 95 per cent of the cropped area is sown east-west or close to it, depending on the shape of the paddock and finding a practical AB line for machinery operations,” says Kim. “It was fairly easy to maintain east-west sowing when we removed the fences and established the block farming layout.”

Another aspect of increasing crop competition is using variable rate technology (VRT) to apply soil amendments and fertiliser. They began in 2010 when they purchased an air-seeder with VRT capability. Over the years, they have seen the benefits of addressing soil limitations where they occur in a paddock, lifting the overall yield and reducing gaps in the crop where weeds can establish.

All crops are currently sown on 250 mm (10 inch) row spacing. However, the Slarkes are changing to a wider (24 m) seeder bar and will move to 300 mm (12 inch) row spacing. This will bring advantages, such as better trash flow and less crop damage, as the risk of soil being thrown into the furrow reduces. However, it also has a potential disadvantage of more light entering the inter-row, allowing weeds to establish.

Over time, the Slarkes have increased their cereal seeding rate from 50 kg/ha to around 70 or 75 kg/ha to increase the crop’s competitive advantage against weeds.

Spray efficacy and efficiency

The Slarkes run an Agrifac self-propelled boom spray with many more spray options than their previous sprayer –enabling them to get better target coverage when applying herbicides. While they have always backed into corners on the outside lap of a paddock, the new boom spray also has turn compensation, ensuring accurate application of herbicides at full rate. They use water-sensitive paper to check spray quality to ensure the sprayer set-up achieves the coverage required for each application. The ability to control individual nozzles provides multiple options for optimal application.

The Slarkes use a standard water rate of 80 L/ha and feel they are achieving effective control with those rates with that boom. If the targets are larger, they drop back to 60 L/ha for summer spraying.

The Slarkes don’t map their weeds besides noting where the weed patches are at harvest. Kim says they have decided to only patch-manage weeds along old fence lines within their blocks. They prefer to apply the same treatment across the whole block to ensure no small patches or individual weeds are missed.

Their Agrifac sprayer can have weed detection cameras added for automated spot-spraying. At this point, the Slarkes can’t justify the cost on their existing machine, even though there would likely be savings in herbicide costs, particularly with their summer spraying program.

Being very wary of spray drift potential, they choose appropriate nozzles and set the pressure carefully for each job. Everyone operating the boom is aware of the risks, and if there’s any doubt, they stop spraying and return when the conditions are suitable. They plan their spray applications carefully, taking into account the wind direction and speed and where crops are out of the ground.

As part of their block farming layout, the Slarkes have created a network of gravelled roads that run along both ends of each block. When spraying, they park the batching truck on the gravel road at one end of the paddock and move it along as the sprayer progresses. The batching station includes a truck carrying a 28,000 L water tank and a trailer carrying the required chemicals in bulk containers. This setup has vastly reduced the time taken to refill the sprayer, keeping it in the paddock for longer within the narrow windows for spraying, and reduced the physical handling of chemicals.

Stopping in-crop weed seed set

The Slarkes use herbicide-tolerant crops, crop-topping, hay production and chemical fallow as their main tactics to stop weed seed set in-crop.

If the crop can be crop-topped, they can sacrifice some yield by going in early and ensuring the weed seed does not mature. They follow up with harvest weed seed control in every crop every year, using Seed Terminator impact mills on their harvesters.

For the last six years or so, they have been growing small areas of export hay in place of a break crop or chemical fallow when annual ryegrass numbers start to creep up.

They occasionally implement chemical fallow, usually on blocks with a large area of ironstone gravel that they want to Reefinate over summer. The window of opportunity to Reefinate an area is relatively narrow, and the operation is more difficult if there is thick stubble on the soil surface.

Mix and rotate herbicide MOA

When new products with new modes of action or use patterns are released, the Slarkes consider whether they have a potential fit in their herbicide program. They like to bring new products into their herbicide program to give the older chemicals ‘longer legs’ and keep their program diverse.

“The new modes of action will often control individual weeds in the population that have a level of resistance to the older chemistries,” says Kim. “But we don’t want to be forced into dropping one group of chemicals just to rely on the new products.”

They use a multi-pronged approach for early weed control to give their crops a competitive advantage. A pre-sowing double-knock is applied whenever an early break brings on a flush of weeds. Their double-knock is typically a glyphosate application followed by paraquat plus a Group 14 [G] spike such as Voraxor (saflufenacil + trifludomoxazin) or Terrad’or (tiafenacil).

Next, a pre-emergent is applied at seeding, and if there is weed pressure in the block, a post-seeding pre-emergent application of a chemical from another group.

The Slarkes conducted an initial herbicide resistance test in 1994 and have only done one more since then because they believe they are doing everything they can to keep weed numbers down and to rotate the available modes of action. If they observe weeds surviving the herbicide program, they change the crop rotation based on those observations.

The initial test showed annual ryegrass resistance to the Group 2 [B] SU herbicides and Group 1 [A] fops and dims. They still use dim herbicides in the rotation to target other problem weeds or volunteer crops in the cereal phase. However, they stopped using fops because they had no place besides ryegrass control. The SU herbicides still provide some control on broadleaf and other weeds in the farming system, so they occasionally still feature in the herbicide program.

“The answer is to use as broad a suite of chemistry as you can,” says Kim. “Back in the 1990s, everyone relied heavily on just a few key products, and chlorsulfuron (e.g. Glean) was a great example. It had a big impact when we lost that option, and we don’t want to experience that again. When we hear people talking about a new product and calling it the ‘new Glean’, it makes us very conscious of the need to use it sustainably.”

The Slarkes use each product for a specific purpose in the rotation and avoid using the same product in the same paddock yearly. The aim is to minimise the use of each product but maximise its performance or effect on the weed population.

Next-level HWSC with Seed Terminator impact mill

In 2006, the Slarkes bought their first chaff cart and began harvest weed seed control. This worked well and had a useful fit with the sheep operation, and a few years later they progressed to a larger chaff cart. The downside of the chaff cart was burning the chaff heaps in paddocks that were to be cropped the following year. Although the weed seeds were collected, they were not all destroyed, particularly if summer rains dampened the heaps.

The Slarkes closely followed the development of the early impact mills, waiting for the mills to be integrated into the header. In 2017, Jamie replied to an ‘expression of interest’ with Seed Terminator, beginning a close relationship with Nick Berry and his team as they further developed their product.

The Slarkes are firmly convinced that the impact mills play an important role in the sustainable use of chemicals and in keeping weed numbers low.

Regardless of which impact mill or other harvest weed seed control method you choose, Kim emphasises the importance of harvesting at the right time. Harvesting early is important, but not too early, so ensure that all the weed seeds are ripe and will separate from the straw. Conversely, avoid harvesting too late when the weed seeds have all fallen on the ground, or the plants have lodged on the ground.

The header needs to be set up to ensure good separation so that all the weed seeds land on the sieves, flow into the chaff stream, and pass through the impact mill (or other HWSC tool).

They see the HWSC tactic as their last chance to get these survivor weeds before they become an issue in his paddocks. To maximise the effectiveness of the operation, they prioritise weedy paddocks for early harvest, cut low, slow down and harvest in the heat of the day (not when the crops are wet with dew) to capture all the weed seeds present.

“We are very confident that the mills are an effective tool in our weed control program,” he says. “Provided we get the weed seeds in the front of the header, we know we are reducing the weed seed bank across the farm.”