Snapshot

• Growers: Derek and Rhonda Young
• Location: Kulin, Western Australia
• Property size: 2903 hectares
• Cropping program: cereals and break crops (wheat, canola, barley, lupins)
• Annual rainfall: 330 millimetres
• Soil pH: 5.5 to 5.9
• Soil types: sand over clay and gravel

Western Australian growers Derek and Rhonda Young estimate they have saved as much as $500,000 over the past decade by switching to optical spraying technology for their summer weed control.

Also known as the 'green-on-brown' spray technique, the system allows for targeted weed control instead of blanket paddock spraying.

Derek says this saving is a conservative estimate and, in some years, he believes he could be saving as much as 93 per cent of summer weed chemical costs compared to the blanket spraying program they were previously undertaking.

The Youngs, who farm at Kulin in the state's central wheatbelt, were the third grain business in Australia to purchase this type of sensor spraying technology when it was imported into the country back in 2009. Being a 'first adopter' can sometimes be a gamble, but Derek says jumping in head-first has paid off.

Given that the initial financial outlay was about $115,000, the savings the Youngs have made since that payment have meant it has been an excellent economic decision for the business.

"Like so many other growers, summer spraying was really frustrating me," Derek says.

"I know we had to do it to get on top of the weeds, but so much of the paddock was bare and we had to spray out so much chemical to target just a few weeds."

He calculated the system would pay for itself in three years.

"But in fact, the savings were so significant that we paid for the technology after the first two years," Derek says.

"My calculations were based on a reduction of spray area to about 10 per cent coverage of the paddock, but even when spraying up to 60 per cent coverage we are still making significant savings."

Derek originally fitted the technology to a boomspray he engineered himself, but he has since fitted the system to a dedicated boom that takes the place of the standard boom on his main sprayer at the end of the growing season.

This technology has been so successful for their businesses that the Youngs now also use it for their knockdown spray prior to seeding, particularly if there has been a late or uneven break.

Since the past three years have seen a very late break, the Youngs have been able to make significant savings on chemicals while still achieving excellent pre-seeding weed control.

The benefits

Derek believes the benefits of using the optical spraying technology are numerous.

Not only are there significant savings on chemicals, but it also allows for more regular and targeted spraying when the weeds are at their most vulnerable.

"Since we don't use as much chemical anymore, the system is much cheaper to run, so we don't wait for all the weeds to germinate to do one blanket spray," Derek says.

Under a blanket spray strategy, the early weeds can often become large, tough and hard to kill.

Derek says earlier targeted spraying also translates into a weed management system that is far more effective and efficient.

"We also have the capability to eliminate difficult weeds such as fleabane and sow thistle with herbicide rates that are not economical in a blanket spray situation."

The limitations

While the technology can be adjusted to suit specific weather and paddock conditions, it has its limitations, particularly in very windy weather.

Derek says he doesn't spray when wind speeds are more than 20 kilometres per hour due to the way the system targets weeds.

"The other issue to be aware of is residual chemicals as one tank load could do anything from 500 to 2500 hectares and we have to be mindful of the following crops," he says.

In-season weeds

After getting on top of their summer weed spraying program using optical spray technology, the Youngs have now turned their attention to managing their in-season ryegrass and radish.

In certain paddocks, Derek could see they were losing the battle against resistant weeds and knew it was time to make some agronomic changes.

Despite the well-known efficacy of trifluralin, particularly on ryegrass, this was one herbicide that Derek and Rhonda did not have access to under their no-till system.

The Youngs participated in the Australian Herbicide Resistance Initiative (AHRI) focus paddock survey in 2018, and ryegrass testing results showed resistance to a range of pre and post-emergent chemistries.

While ryegrass is still very susceptible to pre-emergent chemistry, developing resistance is increasing as growers rely more on these control strategies to combat weeds.- AHRI researcher Dr Roberto Busi

The results showed that, given their reliance on Group J and Group K herbicides, there was developing resistance to prosulfocarb plus the possibility of developing resistance to glyphosate applied at the lower rate of one litre/ha.

Ryegrass also showed resistance to Group B herbicides Imazamox and Imazapyr.

AHRI focus paddock surveys

AHRI has been undertaking random paddock surveys since 1998, with results demonstrating a steady rise in the rate of resistance to post-emergent herbicides, particularly in ryegrass populations, across the grain growing areas of Western Australia.

The latest in this series of GRDC-invested paddock surveys, compiled by Dr Roberto Busi from AHRI in 2018, shows 95 per cent of focus paddocks (not chosen at random) had ryegrass with some level of resistance to post emergent Group A and Group B herbicides.

Dr Busi says Group A and Group B post-emergent selective herbicide are now widely accepted as ineffective on most ryegrass populations and most growers now target ryegrass at the pre-emergent stage.

"While ryegrass is still very susceptible to pre-emergent chemistry, developing resistance is increasing as growers rely more on these control strategies to combat weeds," Dr Busi says.

He says no resistance was found to have evolved to mixtures of pre-emergent herbicides.

"The survey showed how important regular testing is to understand what levels of resistance are occurring on each property in order to make the most effective herbicide management decisions."

Turning the clock back

Since 2003, the Youngs have been no-till farming (full stubble retention) using a disc seeder, which Derek says has worked extremely well, particularly for their canola and lupins.

"But in the past few years we felt our cereals weren't establishing as well and we were limited in our ability use certain chemistries, such as trifluralin, because there was no soil incorporation involved," he says.

In 2018, the Youngs turned back the clock and used a speed tiller (discs, followed by a rolling harrow) for some of their cereal plantings, to ascertain if this would achieve a better result.

"It worked much better than I thought," Derek says.

"This seeding, we put in a quarter of the program using this speed tiller, and while it's not what you would call traditional tillage, it's still incorporating the stubble and allowing us precision seed placement using our existing double disc seeder while applying trifluralin as a pre-emergent to attack the ryegrass and radish."

Derek Young with the disc plough he has incorporated into his weed management program. Photo: Evan Collis

Without being able to clearly identify why this is working for the cereals, Derek believes there are agronomic factors at play, particularly with nutrient cycling following the tillage after many years of zero-till.

"Visually, the wheat and barley that has been planted using this new incorporation method looks much more advanced, and much healthier, than the crops planted under a zero-till system."

While this strategy is working well for the cereals, Derek doesn't believe there is any need to change the way they crop their canola and lupins, which together make up half of their seeding program.

"We are still convinced the canola and lupins need full stubble retention to conserve moisture and to thrive here."

During harvest the Youngs attack the weed seeds with a hydraulic Integrated Harrington Seed Destructor.

As an early adopter, Derek says, the first year was a challenge, but now the system is working well for him and there is no requirement now to burn windrows.

"Being a first adopter of technology can sometimes be frustrating, but it's also very rewarding and can provide us with innovative solutions to some really challenging problems," he says.

"Some farming systems aren't meant to be used forever and I'm always looking for ways to improve our productivity."

More information: Derek and Rhonda Young, dryoung@skymesh.com.au, AHRI fact sheet.