July 2026, AU: Wild radish continues to be an economic headache for growers in the Geraldton region of WA as it can quickly develop herbicide resistance and adapt to changing environmental conditions.
An agronomist and grower for more than 35 years near Yuna, in the northern agricultural region of Western Australia, Belinda Eastough is all too familiar with wild radish (Raphanus raphanistrum) on her own farm and those of her clients.
The region is a low to medium-rainfall zone on Geraldton’s yellow sand plains, with regular liming undertaken to neutralise the otherwise acidic soils. Larger properties principally operate crop rotations of wheat, lupins and canola, while smaller holdings in the medium to high-rainfall regions north of Geraldton may rotate with livestock and pasture.
Along with annual ryegrass, wild radish is a significant economic weed that has developed resistance to multiple herbicide modes of action, forcing growers to develop integrated weed management strategies.
“During the 1990s when the sulfonylurea (Group 2) herbicide products were used, resistance became evident within 3 years,” says Belinda.
“It was typically used twice each year, at pre-emergence and post-emergence, so the wild radish was overexposed to those products and developed resistance very quickly. With annual ryegrass, it took a little longer – perhaps 5 years.”
Adapting chemical resistance
More recently, fomesafen (Group 14), a pre-emergent herbicide, was released for use in narrow-leaf lupins. It is often combined with simazine/metribuzin (Group 5) in mixtures with non-selective herbicides glyphosate (Group 9) or diquat/paraquat (Group 22) herbicides as a knockdown application.
The area already has many populations of wild radish with documented resistance to Group 2 (imidazolinones/sulfonylureas), Group 4 (phenoxys), Group 5 (triazines), Group 12 (diflufenican/picolinafen) and Group 27 (pyrasulfotole). The Group 27 herbicide pyrasulfotole has been instrumental in reducing radish seed-set in cereals. However, there are now multiple populations that have developed resistance to pyrasulfotole.
Wild radish is a very clever plant in that it can evolve and adapt very quickly. Just when you think you have a strong management solution, it can outsmart you.
“As we spray earlier, we are selecting for later-germinating wild radish. When we crop-top at harvest, we select for radish that sets seed earlier with pods lower down the stem. The genetic diversity in wild radish is amazing.”
Mixing up the modes of action – a 2-spray strategy
Resistance to products containing Group 27 herbicides (i.e. pyrasulfotole) is increasing. The most effective herbicide strategy is proving to be mixing and rotating the modes of action with application at the 2 to 4-leaf stage.
Belinda describes the ‘2-spray strategy’ as a mixture of groups applied pre-emergence, followed by a post-emergence application utilising 2 different modes of action. Group 9 (glyphosate), Group 22 (paraquat, diquat), plus a Group 14 option are the most popular for radish control.
“In difficult-to-control populations of radish in wheat post-emergence, we will go in early with a Group 12 (diflufenican/picolinafen) mixed with a Group 6 (bromoxynil) and possibly a Group 4 (MCPA). This is then followed up with pyrasulfotole products mixed with a Group 4, which are your MCPA/2-4,D products.
“By doing this, multiple modes of action are utilised, combining to provide effective levels of control at label rates. This strategy also slows the development of herbicide resistance,” Belinda says.
Mechanical control methodologies
In the past, mechanical attempts to control wild radish have included chaff lines and chaff carts. However, in a drought year there is less biomass and the chaff lines are not heavy enough. Belinda says in those seasons it doesn’t rot the weed seeds, creating a weed nursery. As a consequence, growers can end up with strips of wild radish through the paddock where the chaff lines were put down.
Weed seed mills are an incredibly effective tool in controlling weed seed. Some growers in the region use these, but the weed seed mill approach can limit the farm’s header capacity. Growers may only have an impact mill on one of the headers, but not on all.
Windrow burning is also a useful tactic to drive down the seedbank of wild radish and ryegrass. However, as wild radish is hard-seeded, it takes a hotter burn than ryegrass to destroy the seed.
Feed the crop not the weed
Targeted nutritional applications are an important strategy for growers in the Geraldton area. By applying fertiliser in bands under the crop seed at planting, it is available to the plant and less available to the wild radish. Liquid fertiliser applied in a band via streaming nozzles once the crop has emerged will also give the plant a boost for early vigour.
By giving the crop a nutritional boost early in development, crop competition adds to the suppression of wild radish.
Systems and crop rotation
Crop rotation and breaks will also reduce seedbank levels and slow herbicide resistance. Larger, lower-rainfall properties use chemical fallows as a weed control option as well as an opportunity to store soil moisture on red loams. Smaller enterprises look to crop rotations of wheat, canola, lupin and pasture.
Crop rotation is proving to be an effective element of the overall weed management strategy, particularly when using glyphosate-resistant varieties of canola.
“For those larger, lower-rainfall growers, using a chemical fallow means they can employ many different herbicide groups in one year and get on top of problematic weeds such as annual ryegrass and wild radish.
“Many of the smaller growers carried sheep, but with the change in policy for live export, many have transitioned to crop rotations instead of using livestock as the crop break. When they had the livestock, they would do spray-topping at seed-set in the spring.”
Management extremes
In the Yuna/Northampton district where Belinda operates, 2 properties have been diligent with wild radish management since the 1950s. By handpicking the weed as it shows itself, they’ve kept the seedbank very low. Any wild radish on these properties is generally on fencelines, blown in from other farms or roadsides, and easily mapped and dealt with.
Belinda noted that while most growers do not have the capacity to handpick, it does show that diligence in controlling the seedbank is vital. Not only does it save the growers tens of thousands of dollars in chemical inputs (both these properties have cropping programs more than 4,000 ha) and improve yield, but it also lowers the risk and speed of herbicide resistance developing.
“Our region is the home of wild radish and herbicide resistance. What we have learned about its control and management is taken on board very quickly. It is such an adaptable plant. In a drought year, it will be stacked with pods by the end of July. Understanding its behavioural growth and genetic variability is a major consideration in managing wild radish. An integrated, evolving plan is the only way to stay on top of this challenging weed.”
Farm snapshot
Located at Yuna, north-east of Geraldton, Belinda and her husband, Ashley, crop between 4,500 and 5,000 ha a year. About half this will be wheat, with another 1,500 ha in narrow-leaf lupins and 800 ha of canola.
The property also supports permanent pasture paddocks seeded with clover species to run Merino and Poll Dorset sheep. The sheep are grazed on the winter pasture and then stubble for the summer.
Describing the property as experiencing variable rainfall, Belinda says 2025 was exceptional with 360 mm of rain, but recent years have seen rainfall as low as 167 mm in 2019 and 147 mm in 2023.
As a sandplain, the soil can be quite acidic with a pH below 4.5 calcium chloride. Belinda’s family have been applying lime since the 1990s to improve the soil for cropping.
“The real game changer for our farm has been soil amelioration and deep ripping,” says Belinda. “Soil amelioration and deep ripping, as well as using a Plozza Plow to invert the soil, have been vital here. Especially to incorporate the lime and alleviate non-wetting issues for the wheat.
“We prefer to do it after rain to minimise any wind erosion. We have been deep ripping for 30 years. We used to go down to 30 cm but now go to a depth of 50 to 60 cm. It has given us improvements in soil management and crop yield, and also from a weed control point by burying our weed seeds.”
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