Herbicide hangover troubles crop selection

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Plant breeding and technology have boosted crop productivity but weed managementhas become the issue shaping crop selection in the Victorian Mallee


Growers: Murray, Neil and Rohan Mott
Location: Turriff East, Victoria
Farm size: 12,000 hectares (owned, leased and share-farmed)
Rainfall: 250 millimetres
Soil types: variable sand/clay, sand/limestone, clay, deep sand
Soil pH: neutral to alkaline
Enterprises: cropping only; wheat (42 per cent), barley (24 per cent), lupins (20 per cent), field peas, vetch and lentils combined (14 per cent)
Typical crop rotations: wheat/barley/legume

Farming in Victoria’s Mallee region, Rohan Mott was more than happy with his first crop of Compass barley, which yielded four tonnes per hectare in November from only 125 millimetres of growing-season rainfall. Significant rain in mid-January 2015 contributed to this result.

Compass was commercially released in 2015 and is showing early promise in the Mallee as a replacement for the malting variety Commander, although it is not expected to gain Barley Australia malting accreditation until 2017 at the earliest.

However, brewers around the country and internationally have their own malting specifications and are already showing strong interest the variety. In South Australia, Glencore Grain provided some segregation for the 2015 crop.

At Turriff East, in north-western Victoria, the Motts are making good use of the family’s on-farm storage complex to provide their own segregation while working to direct-market the crop with a malting company and other contacts.

Rohan farms with his brothers Murray and Neil, and their father Graham is also still active in the farm’s operations. They crop 12,000 hectares that stretch between the Calder Freeway and Sunraysia Highway at Turriff East, south of Ouyen.

Compass, Rohan says, is a good example of the improvements in varietal performance over the past decade that have made a big difference to farm productivity and performance. The Motts grew three barleys in 2015: Scope, Gairdner and Compass. Compass was one of their highest-yielding barley crops ever.

Barley accounted for 24 per cent of their 2015 grain crop, with additional plantings planned for 2016. Compass is likely to replace Gairdner and Rohan will also plant a small quantity of the soon-to-be-released Clearfield variety Spartacus CL, bulking up seed in preparation for the commercial release as a replacement for Scope.

Herbicide residues

Rohan says Clearfield technology has been an important part of their weed-management strategy, but he is wondering if there has been an over-reliance. He and many other growers across the Mallee are reporting chemical residues affecting crops 12 months – and even two years – after the chemicals were used.

“We don’t do specific testing for the chemicals but, visually, you can see the effects in a crop and at the end of the season, particularly compared with similar crops across the farm where imidazolinone herbicides weren’t used,” Rohan says.

In one instance, he planted lupins following a Clearfield wheat crop. All but one hectare of the wheat received an in-crop imidazolinone application. After running short of chemical they decided the remaining patch of crop was small enough and clean enough to leave unsprayed.

The shortfall provided an accidental test-strip that demonstrated the effects of herbicide residues on the next crop. Rohan says that in the following lupin crop the area corresponding to the unsprayed patch was clearly healthier and more productive than the rest of the paddock.

He has also mapped the performance of crops following summer applications of a phenoxy herbicide, with a clear demarcation in crop health between the sprayed and unsprayed areas. As a precautionary measure, he now plants Clearfield varieties in paddocks the year after Group B imidazolinone products have been used.

The extended effects of herbicide residues in the region warrant further investigation, Rohan says. He believes low rainfall and low soil organic matter contribute to the problem; although, that said, the Motts have been seeing definite improvements in their soils since selling their livestock in 2002 and moving to no-till in 2004. There has been less erosion of sandy soils and the productivity of sandhills has improved. Soil organic matter has also increased over the past decade.

Herbicide alternatives

Nonetheless, the potential for herbicide residues adds another element to the already difficult task of juggling conventional and Clearfield crops, seasonal conditions, market outlooks, rotations and weed control. In the past year, the Motts have introduced two alternative weed-control strategies to help reduce their reliance on herbicides.

Their vetch crop was desiccated with glyphosate before being cut for hay, allowing it to be harvested before weed seed-set. They also windrowed the chaff from their 2015 cereal crops in paddocks with a higher weed burden, burning it when weather conditions permitted.

He says the 2015-16 summer has been even drier than the previous year, which has kept the risk of herbicide residues front of mind in his crop selection for the coming year. This will include a barley crop, to be cut for hay before weed seed-set, in order to reduce the grass weed burden.

Crop mix

Their 2015 wheat crops included LongReach Scout, Corack, Grenade CL Plus and Kord CL Plus, and while quality and test weight were all were good, yields were below potential. In 2016, they planted LongReach Scout and Kord CL Plus, which will help to bulk up seed for the newly released Scepter variety, which is expected to replace Mace. “I think the yields are similar to Mace, but there are some improved agronomic traits,” Rohan says.

In the future overall crop mix, wheat plantings are likely to be reduced to make way for more barley and legumes.

In addition to vetch, the Motts also grow lupins, lentils and field peas. While there are undoubtedly nitrogen benefits from the pulse crops, Rohan says he views them more as valuable cash crops: “Sometimes lupins provide our best gross margin, and they don’t dry out the ground as much as vetch or canola.”

Like many other growers in the Mallee, canola is no longer on his program.

Business efficiencies

The Mott brothers have been farming together for decades, under the guidance of their father Graham, later buying their own properties. They shared labour and machinery, but made farming decisions independently. However, in the past eight years, as part of their family succession planning, they have established their own independent operations as shareholders of a single larger enterprise that farms their combined holdings.

Rohan says pooling their resources in this way has provided efficiency gains and allowed them to increase economies of scale, including facilities such as on-farm storage, which can now hold 16,000t of crop. They do all their own market trading, which makes the storage essential for optimising prices.

It has also allowed them to invest in the latest equipment and to replace it regularly.

Benefits of new equipment include easier maintenance, fewer breakdowns and access to the latest technology. The Motts have been using variable-rate technology for seed, fertiliser and fungicides for seven years, combined with paddock and yield mapping to optimise inputs. During the 2015 harvest they also subscribed to John Deere’s Machine Sync system for the first time.

“We can have multiple machines in the paddock and we can see exactly what each is doing, which allows us to coordinate them more effectively; the harvester can control the speed of the chaser bin while unloading, which makes it much easier for the drivers.”

Rohan sees technology as important to improving productivity. Moisture probes are his latest addition to the toolkit. He has joined an informal group of 12 local growers linking soil moisture probes and their weather station data. There are two probes on the Motts’ property and 20 in total among the group.

“We are hoping to use the data to better understand our soil-moisture profile, and to improve planning and fertiliser management. I am always looking for any innovation that can improve what we do.”

As a recently appointed member of the GRDC’s Southern Panel, Rohan says it has been interesting during his first few months with the panel to see how different areas have taken to different types of technology. “In the north-west, variable-rate technology is widespread, while in the north-east, controlled-traffic systems seem to be more prevalent. It’s also interesting to understand the issues that are of concern to growers everywhere, such as nitrogen use efficiency,” he says.

Portrait of Rohan Mott

Rohan Mott with one of his best-ever barley crops, planted into field pea stubble with two pre-sowing herbicide applications (after summer rain sprouted weeds) and one in-crop application.

PHOTO: Catherine Norwood

More information:

Rohan Mott,
0429 701 170,


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