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Cost-effective dual HWSC modes

Over the last few decades, innovative Australian growers have invented novel designs and made critical improvements to harvest weed seed control machines such as impact mills and chaff carts.

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, in southern WA. They use two modes of harvest weed seed control to maximise feed value for their sheep and minimise the impact of burning chaff.

With high weed seed contamination in their grain in the 2000s, Craig and Sara 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, the Bignalls purchased conveyor-type carts. Along with being another weed management tool, the chaff carts also provided a valuable fodder source for the Bignalls sheep flock.

Having keenly watched the development of the Harrington Seed Destructor impact mill, Craig invested in a hydraulic-drive 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 and his father Dan 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, the manufacturers 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 problems on the original iHSD.

These days, Craig has a vertical iHSD on one header and a chaff cart on the other. The Bignells only run the chaff cart 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.

The feed value for livestock grazing chaff heaps is about 2530 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.

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 Newmans HWSC costs calculator shows that chaff carts and the iHSD cost about the same to run, but Craig finds that the iHSD is significantly more costly to own than the chaff cart, especially when depreciation costs are considered.

Harvest weed seed control is integral to the Bignell’s integrated weed management program, alongside strong crop competition and effective herbicide use, to reduce the impact of herbicide resistance on their mixed farming enterprise.

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.

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

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!

Crop competition is foundational for weed control as trials repeatedly show that ryegrass seed production doubles in poorly competitive crops, he says. 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.

The Bignells use multiple herbicide and non-herbicide weed control tactics in the WeedSmart Big 6 strategy to keep their weed numbers as low as possible. The latest weed control tactics and technologies will feature at WeedSmart Week in Port Lincoln on 29–30 July 2024.

More resources

Craig Bignell and Sarah Robinson case study

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