James Pursehouse, Breeza, NSW

Andrew and Cynthia Pursehouse and their eldest son James have recently ‘employed’ a Swarmbot named ‘Mooki’, fitted with a 13 m RBE boom and Weed-IT Quadro sensors as their dedicated fallow spot-spraying unit to work within their 2200 ha dryland cropping program.

The Pursehouse family owns and operates ‘Breeza Station’, a 5100-ha mixed farming operation near Gunnedah on the Liverpool Plains, NSW, growing irrigated and dryland crops and running a self-replacing Angus cattle breeding operation.

The Breeza Station aggregation is a single parcel of land with the Mooki River forming the northern boundary. Their cropping program consists of 2200 ha of dryland and 1100 ha of irrigated production of wheat, durum, chickpeas, faba beans and canola in winter and cotton, corn and sorghum in summer. James says their diverse crop rotation allows them to rotate several herbicide modes of action to minimise the risk of herbicide resistance.

“Canola is a minor part of our rotation now, but we may include it more frequently in the future,” he says. “Canola offers additional options to diversify our weed control program.”

The Pursehouses switched to no-till farming in 1993 and implemented a controlled traffic farming system on 2 m centres and 8 m machinery widths in 1996. In 2012, they moved to a CTF system on 4 m centres and 12 m widths. In 2015, they adopted automated weed detection and spot-spraying technology to reduce their chemical use in fallow fields.

Automated spot spraying fallow weeds uses less chemical per spray pass, representing significant savings to their business. James gives an example of spraying 860 ha of wheat stubble with weed coverage of 5.4 per cent early in the year. To blanket spray this paddock would have incurred an additional $16,000 in chemical costs for an ester/glyphosate application, using relevant rates for blanket spraying and optical spot spraying.

Automated spot spraying is a valuable tool in the WeedSmart Big 6 toolbox. It reduces herbicide resistance risk through timely application on small weeds alongside a diverse cropping program and herbicide rotation.

“Although the 36 m Weedseeker boom on our Miller Nitro SP worked well enough, we were finding that we frequently needed that machine to do two jobs at the same time,” says James. “The in-crop blanket spraying usually had priority over spot-spraying the fallow area, so we started looking for ways to increase our spray capacity.”

The family investigated their options and weighed up the pros and cons of buying a second self-propelled sprayer or an autonomous (robot) spot sprayer. While both are expensive pieces of machinery, the benefit they saw in the robotic option was the ability to do two spray jobs simultaneously without needing an extra operator.

In 2022, they decided to order a robotic platform from SwarmFarm as a dedicated spot-spraying unit, and it was deployed on Breeza Station in June 2023.

“In the 14 months between June 2023 and August 2024, the Swarmbot completed 1490 engine hours, which includes time travelling, spraying and in sleep mode,” says James. “It has an average operating speed of 9.7 ha/hr, uses 0.8 L/ha of diesel, and has a running cost of $4/ha.”

In comparison, their SP sprayer typically covers 50 ha/hr and uses 0.9 L/ha of diesel when camera spraying, giving a similar running cost per ha, plus a driver.

James says they have made a major shift from reactive to proactive weed management, where they are now targeting smaller weeds more often using a spray rotation of three to four weeks, according to weather conditions.

“We’re not holding off spraying to wait for a few more weeds to emerge,” he says. “We are just sending the robot around knowing that if some very small weeds get missed, we’ll get them next round.”

“All weeds are more susceptible to herbicide when they are small,” he says. “The fact that the robot will return to each paddock within a few weeks means that we are continually driving down the weed seed bank by eliminating small weeds before they can establish and set seed.”

The main hard-to-kill fallow weeds on Breeza Station are milk thistle, fleabane, ryegrass, windmill grass, and barnyard grass. Spot-spraying is an excellent option to reduce chemical use and also allows the Pursehouses to use a selection of herbicides at higher rates registered for optical spot-spraying.

“Because we are always targeting small weeds, the robot is making a noticeable difference to the density of these hard-to-kill weeds,” says James. “We use a few different mixes depending on the weed spectrum and use the double knock approach in some fields. Mostly, we use a single pass of Terrad’or plus 2,4-D Ester in winter or Starane Advanced in summer, in the robot’s tank with Hasten and Gramoxone Pro, all at registered rates for optical spraying.”

Spot spraying is done in paddocks with a fallow weed density of 0.4 to 26 per cent. If the weed density is over about 30 per cent, the field will be blanket sprayed. James says their use of residual herbicides in fallow is increasing. Their row spacing of 33 cm for winter crops and 1 m for irrigated crops does not provide a high level of crop competition, so starting the cropping phase with low weed seed numbers is critical to take the pressure off their in-crop herbicides.

To comply with their controlled traffic system, ‘Mooki’ has 4 m centres and a 13 m RBE spray boom. This is standard for 12 m CTF systems to provide a 0.5 m overlap for each pass. The platform carries a 1500 L spray tank and weighs about 5 t when fully loaded.

“When the Nitro SP weighs about 20 t when it is fully loaded, so the robot has a distinct advantage when it comes to minimising compaction and getting onto paddocks sooner after rain,” says James. “We selected 1400 mm high-clearance chassis so we didn’t lock ourselves out of future use opportunities such as inter-row spraying in skip-row cotton crops.”

James says they are achieving more accurate weed detection with the 13-m boom on the robot travelling at a ground speed of 10 km/hr, compared to the 36-m boom with front-mounted cameras on the self-propelled unit working at 15 km/hr.

“The 13-m boom is very stable compared to the 36m boom, where the outer boom sections can sway back and forth, causing misfires,” he says. “The robot gives us a consistent 50 cm boom height and slower operating speed, so the sensors detect very small weeds in heavy stubble.”

Since adding Mooki to the farm workforce, the self-propelled sprayer’s engine hours have been reduced, extending its effective life. Staff time and skills have also been better utilised.

“At cotton picking time, the whole team can focus on picking and mulching jobs knowing that Mooki is attending to the fallow spraying,” says James. “This means all jobs are being done on time, and we don’t have to worry about the fallow weeds depleting our stored soil moisture or setting seed. And none of us wish we were out spot spraying!”

Boundary and obstacle mapping are important parts of the setup phase of robotic systems. James uses John Deere Greenstar guidance lines, which he exported directly from the John Deere Operating Centre into the SwarmFarm Farm Manager program, saving a lot of time on boundary mapping. They chose to use the SwarmFarm receiver unit rather than the John Deere receiver.

“Our whole farm is within one boundary, which also made the mapping easier, and we have the added benefit of not having to tow the robot between farms,” says James. “It pays to keep your headlands smooth and to get the mapping right for the obstacles, fields and roads. We drove around with the bot the first time it worked in a new field to make sure everything was mapped correctly. We reduce the operating speed to 6 or 7 km/hr for the first pass after wheel-track renovation in a field.”

The Pursehouses are working on setting the bot up to navigate head ditches in irrigated cotton fields and preparing a re-fill trailer so the bot can spend more time spraying. They also plan to link the robot’s onboard weather station to the WAND tower on their farm to access more local weather information relevant to suitable spraying conditions.