Refining the double-break tactic

Brothers Rhys and Joel Curr farm with their partners and parents, Andrew and Belinda, on a 5800-ha aggregation of owned, leased and share-farmed blocks within a 45-km radius near Trundle in the Central West of NSW.

Having sold the last of their sheep in 2023, the Currs are doing more summer fallow spraying and using a double-break phase to clean up winter weeds. Rhys says they have a similar management system across the whole aggregation, regardless of land ownership. Their weed management program includes tactics from each component of the WeedSmart Big 6 to keep their weed numbers low within a profitable farming system.

The Currs run a winter cropping program that begins with a legume crop (vetch, lupin or field pea) followed by canola before moving into a cereal phase of wheat, barley, wheat. They have implemented a block farming system that includes 2000 ha wheat, 1000 ha barley, 600 ha vetch, 1000 ha pulse (lupin and field pea), and 1000 ha canola most years. Rhys finds this rotation works well in their 450 mm rainfall zone, although canola can struggle in drier years.

“The legume followed by canola provides a double-break for grass weed control and allows us to target problem weeds, like wild oats with resistance to Group 1 fop chemistry,” says Rhys. “We have been growing brown manure vetch for more than four years and have observed multiple benefits to our cropping system, including a significant saving on nitrogen fertiliser across the business.”

The vetch brown manure is good for soil structure, provides a longer fallow for weed control and contributes about 200 units of fixed nitrogen to the soil, sufficient for the following canola crop.

“We spray out the vetch in September and leave the crop residue in place to increase rainfall infiltration and conserve soil moisture over summer,” he says. “We spray any summer weeds that emerge, and the crop residue is easy to plant through in the next season.”

On their share-farmed and leased blocks, the Currs use a narrow leaf lupin or field pea crop ahead of canola as the double-break rather than vetch brown manure. Wherever possible, they avoid planting wheat on wheat.

“Growing grain legume crops for harvest is also very beneficial to our rotation,” says Rhys. “We still gain soil health benefits, including slow-release soil nitrogen. As a result, the following canola crop requires only about 50 units N to compensate for the nitrogen removed in the lupin and field pea grain. Regardless of the pulse crop grown, the following canola yields are up around 3 t/ha, and the yield is always higher than if canola follows a cereal.”

Canola relies on good soil moisture through the profile, so the Currs don’t plant if there is insufficient moisture. In their region, this happens about 1 in every 6 years, and they usually grow a cereal crop in these drier years instead. They currently grow hybrid TT canola varieties, HyTTec Trifecta, HyTTec Trophy, and Hyola TT Blazer, and would consider growing Clearfield canola varieties in the future.

By building up the soil nutrition using legumes, reducing compaction with controlled traffic farming and addressing soil constraints, the Currs are increasing the competitiveness of each crop against weeds while optimising grain yield.

“We have conducted soil mapping for pH and phosphorus deficiency and are addressing soil constraints with lime, gypsum, sulfur and phosphorus as required using variable rate applications,” says Rhys. “In the sodic areas, we are deep-ripping and incorporating the gypsum.”

The Currs initially submitted weed seed samples for herbicide resistance testing after clodinafop (Group 1, Topik) failed to control wild oats. They have since tested annual ryegrass, which had medium resistance to pinoxaden (Group 1, e.g. Axial). However, Axial still works well for wild oats and remains in their program.

Rhys says that now that they are cropping their land more intensively, they expect that more instances of herbicide resistance will arise, but they want to slow the process as much as possible by being proactive with their weed control program.

“The brown manure phase is a key component in our program to keep weed numbers low,” says Rhys. “We are doing our best to maximise the efficacy of each herbicide we apply, like using mid to high-range label rates, keeping water rates up and spraying when conditions allow the herbicides to work well.”

The double-break is a proven tactic for reducing the annual ryegrass seedbank. When the Currs started using the vetch brown manure tactic a few years ago, they didn’t apply any grass herbicides while the vetch was growing. Rhys says they noticed that this resulted in the establishment of some large grass plants in the vetch that either set seed before it was time to spray out or were too large for the double-knock to kill completely.

“We were putting too much pressure on the double-knock at the end of the vetch phase, so now we spray clethodim during the growing phase of the vetch to stop the grasses setting seed and ensure that any grass plants present at the end of the vetch season are small,” he says.

Registrations are now open for WeedSmart Week 2025 in Geraldton, WA on 29 and 30 July, showcasing how growers use the Big 6 tactics to keep downward pressure on the weed seed bank.