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Craig Bignell & Sarah Robinson, Broomehill, WA

On-farm weed control innovation success

Craig Bignell and his wife Sara Robinson run a 9500 ha mixed farming operation on several blocks within a 50 km radius of their home farm at Broomehill, near the southern edge of the West Australian wheatbelt.

Craig’s parents, Dan and Helen, are also involved in decision-making on the farm. Dan has passed on his farm engineering skills to Craig, and together, they have designed and built a variety of farm implements. One is the prototype mechanical-drive vertical iHSD that they built in their farm workshop, which iHSD manufacturers, de Bruin Engineering, has since adopted.

Using all the tactics in the WeedSmart Big 6 program is keeping weed numbers down and reducing the impact of herbicide resistance on the Bignell’s mixed farming enterprise.

Crop and pasture rotation

The Broomehill area receives a fairly reliable 400 mm of rainfall annually, allowing the Bignells to grow various crops, including wheat, barley, oats, canola, lupins, faba beans, and vetch. The vetch is grown only for grazing, and in recent years, oaten hay production has been added to the crop rotation.

The usual rotation for a paddock is either cereal/canola/cereal or legume/wheat/canola/cereal, depending mainly on soil type. Crown rot in wheat has become a problem in some paddocks, and Craig is trialling a double-break system to interfere with the crown rot cycle and reduce weed numbers.

“Dad followed a lupin, canola, wheat, wheat rotation and didn’t have crown rot,” says Craig. “We are trying canola/canola or legume/canola followed by two cereals to address crown rot in particular blocks.”

About 70 per cent of the total farm area is cropped, and the remaining area is either rotating through a pasture phase or salt-affected country that they have sown to perennial pasture for their Merino and Suffolk-cross sheep.

In winter, the sheep graze mostly on annual pastures and vetch crops, and the perennial pastures of saltbush, tall wheat grass and balansa clover, established in the early 2000s, help fill the autumn feed gap. The sheep also graze on chaff heaps after the legume and canola crops and in cropping paddocks during a pasture phase for weed control.

If ryegrass numbers increase in a paddock, Craig will shift it into a 3 to 5-year pasture phase to drive down the weed seed bank. This usually occurs on 2 to 5 per cent of the cropped area each year. Grazing pressure from the sheep and pasture manipulation to increase clover dominance over the grasses works well to exhaust the grass weed seed bank. Pasture-topping is used during the pasture phase but severely impacts stocking rates. The pasture is sprayed out with paraquat before returning the paddock to cropping with low weed seed numbers.

Crop competition critical

Craig considers crop competition one of the most important tactics for controlling annual ryegrass. Ryegrass is their most challenging weed, and as Craig says, even when they do everything they can to control it, they still have plenty of it!

“If we didn’t throw everything in the Big 6 strategy at ryegrass, I really don’t think we would still be growing crops,” he says. “Crop competition is foundational for weed control as trials repeatedly show that in poorly competitive crops, ryegrass seed production doubles. We use competitive cultivars, high seeding rates, east-west sowing, narrow row spacing and early sowing – all to maximise early crop vigour and quickly close the canopy.”

Barley is the Bignell’s most competitive crop. They often favour planting barley rather than wheat, particularly where weed numbers are increasing slightly. Planet and LaTrobe barley are working well for them, sown at around 90 kg/ha, resulting in cleaner paddocks.

The wheat crops are sown at a slightly higher seeding rate of 100 kg/ha. All crops are sown on 25 cm (10-inch) row spacing and aligned east-west wherever possible.

“East-west sowing is something I’d rather not bother with, but the fact is that it has about the same impact on weed seed numbers as harvest weed seed control does,” says Craig. “Trials at Katanning showed a 50 per cent reduction in ryegrass seed production between crops sown east-west and others sown north-south. We can’t afford to ignore this big free kick, so we have done what we can to make it work in most of our cropping paddocks.”

In the last few years, the Broomehill area has had good early breaks that allowed a pre-seeding double-knock, but Craig is happy to dry sow when the season dictates. He says it is rare that the whole program will be sown dry and that sowing on time is vital for early crop competition. He also applies nitrogen early to get the crop well-established quickly. Their crops also respond to trace elements such as copper (applied most years for cereals) and zinc.

The main soil types on the Bignell’s farms are sandy duplex, red and grey clay and gravel, and sometimes these soils can all be found in a single paddock. Over the years, the Bignells have implemented numerous soil amelioration treatments, including applications of lime and gypsum, as well as topsoil inversion using a mouldboard plough, Plozza plough, or offset discs. Most of these treatments have been done on their sandy soil types, sometimes in patches within a paddock.

Profile inversion and mixing are used mainly to improve the wettability and water-holding capacity of sandy soils. However, these tactics have not been particularly effective at resetting the weed seed bank in treated paddocks.

Spray efficacy and efficiency

With several properties spread around the district, the Bignells have prioritised efficient logistics for their machinery, including spraying gear. Craig has a practical, low-key batching system that moves to each farm with the sprayer and allows efficient refilling. He also has water available at strategic points around the farms.

The Bignells employ three full-time workers on the farm, and Craig values all opportunities for him and his employees to attend courses together. This way, everyone is up-to-date with spray application practices and laws related to moving machinery between properties.

“We value good professional advice and use good operators who care about doing the job right,” says Craig. “It is also crucial to return to the paddock to observe the result of herbicide applications. We don’t do any weed mapping, but we keep a notebook in the header to record areas of ryegrass and radish present in each paddock.”

Craig uses high water rates (usually 100 L/ha) to ensure the spray job is done well and follows the label instructions for rates and boom set-up. The double-knock tactic is an integral part of their weed control program.

For many years, the Bignells engaged a contractor with a WEED-IT boom for automated spot-spraying summer weeds, and have recently purchased their own WEED-IT boom.

Stopping weed seed set

As the cropping season progresses, Craig looks for ways to prevent late-germinating weeds from flowering, setting seed and adding to the weed seed bank. Each season, they choose a variety of herbicide and non-herbicide tactics to suit the crop and weed profile in each paddock.

Crop-topping is their mainstay tactic to prevent weeds from setting seed in pulses. In the past, they have also found desiccation in feed barley very useful in some years.

Swathing cereal crops growing in problem paddocks provides a non-herbicide option to reduce weed seed shedding, particularly ryegrass, before harvest. Hay production is another highly effective mechanical weed control tool that the Bignells have recently brought into their rotation.

To help run down the weed seed bank, Craig occasionally does an ‘autumn tickle’ to initiate weed seed germination. This allows him to target an even flush of young seedlings with a double-knock treatment before seeding.

Mix and rotate herbicide MOA

Herbicide resistance is at the forefront when Craig plans their crop rotation and herbicide program. He is aware of areas of the farm where the ryegrass is resistant to clethodim (Group 1 [A], e.g. Select), and assumes that glyphosate-resistant ryegrass is also present on the farm.

Diclofop-methyl (Group 1 [A], e.g. Hoegrass) is no longer used, and there is only minimal use of sulfonylurea (SU, Group 2 [B]) herbicides in their program.

“Glyphosate resistance in ryegrass is our greatest concern, so we are managing our paddocks accordingly,” he says. “I am also concerned about herbicide resistance building in capeweed and wild radish, and try to learn from the experience of growers in other areas facing these problems.”

To help protect glyphosate, Craig mixes clethodim with glyphosate and follows each glyphosate application with paraquat.

Their diverse crop rotation enables the effective rotation of herbicide modes of action applied to each paddock. Herbicide-tolerance traits in canola further add to the diversity of the crop rotation – Craig plants one-third of their canola area to Round-Up Ready (RR) hybrids, and the rest is sown with triazine-tolerant (TT) hybrids.

“New herbicides are expensive, but so is resistance,” says Craig. “We are using more and more of the ‘expensive’ and newer chemistry in our program now. We also try to keep up to date with the research around effective tank mixes, particularly for the newer pre-emergence herbicides – and that’s been good for us.”

Craig usually applies trifluralin (Group 3 [D], e.g. Treflan) mixed with another pre-emergent product such as Sakura, Luximax or Overwatch in their cereals. Where pre-emergent herbicide products have multiple registered use patterns, he also looks for strategic opportunities to vary application timing.

He is using mixes, including Treflan, Reflex, Terbyne, Propyzamide, and Ultro in their legume crops, and Treflan, Propyzamide, and Overwatch in their canola crops.

Whether products are applied singly or in a mix, Craig always uses lethal doses of all chemistry applied. Their agronomist is integral to all their herbicide decisions.

Dual HWSC capitalises on strengths

Faced with high weed seed contamination in their grain in the 2000s, the Bignells decided to introduce harvest weed seed control to their weed management program. In 2008, they purchased two chaff carts, one for each header. The early model chaff carts were blower systems that experienced some weed seed losses, so when they replaced their headers, they purchased conveyor-type carts.

Having keenly watched the development of the Harrington Seed Destructor impact mill, Craig invested in a hydraulic-drive integrated Harrington Seed Destructor (iHSD) impact mill in 2015. Unfortunately, the early models experienced several setbacks, and the Bignells ended up with a collection of spare parts in their shed. Craig took these parts and followed a hunch that resulted in the prototype of the mechanical-drive vertical iHSD that is now on the market.

Their prototype machine had many problems, but they ran it for 400 hours in the 2017 season. Soon after, de Bruin Engineering adopted the idea and developed the vertical iHSD that runs off the chopper drive and down to the mill, eliminating the hydraulic system that had caused many problems on the original iHSD.

Although managing chaff heaps is challenging, they are a valuable fodder source for the Bignell’s sheep flock. Ed Riggall from AgPro Management, Mt Barker, WA, has shown there is a 2.4 kg average weight gain benefit for grazing chaff piles over grazing stubbles.

The feed value for livestock grazing chaff heaps is about 25–30 per cent higher than that of paddocks harvested with the iHSD and paddocks without any HWSC tool on the header. For these reasons, the Bignells were keen to keep using the chaff cart system in their operation.

The Bignells now run the chaff cart only in their legume crops, avoiding the fire risk that burning cereal chaff heaps poses. This also reduces the wear-and-tear on the impact mills that can occur when harvesting legumes. The legumes produce less crop residue, reducing the need to burn while providing high-value feed for their livestock.

Craig now has a vertical iHSD on one header and a chaff cart on the other. With both systems, it is essential to harvest low and ensure good separation of chaff and straw in the header set-up. This maximises the quantity of weed seed that enters the header and keeps the weed seed in the chaff stream to be processed through the mills or collected in the chaff cart.

Peter Newman’s cost of HWSC calculator shows that chaff carts and the iHSD cost about the same to run, but we find that the iHSD is significantly more costly to own than the chaff cart, especially if you consider depreciation.

Harvest weed seed control is integral to the Bignells’ integrated weed management program, capturing and destroying weed seed that has evaded control through the growing season.

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