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Harvest weed seed control embraced to target escapes

Stewart Wallace in one of his canola crops on his farm north-east of Esperance, Western Australia.
Photo: Jessica Wallace

Harvest weed seed control is enabling Stewart Wallace to drive down the population of herbicide-resistant weeds on his Western Australian farm.

Stewart and his partner Jessica farm 3000 hectares of sandplain country at Neridup, north-east of Esperance, where the average annual rainfall ranges between 480 and 550 millimetres.

He told a recent WeedSmart webinar that his most problematic weeds were annual ryegrass, brome grass and wild radish.

Keen to prolong the effective life of available herbicides, Stewart started using chaff carts in 1997.

Chaff carts are towed behind the harvester to collect weed seed-laden chaff. The material is dumped into piles for later grazing by livestock or burning.

In 2017, with a rotation of 1000ha of wheat, 1000ha of canola and 1000ha of barley, Stewart said that wild radish and annual ryegrass were becoming serious problems.

He ran the chaff cart until 2019 when he bought a John Deere S790 harvester fitted with a Redekop Seed Control Unit (SCU) and MAV straw chopper.

The Redekop comprises two mechanically driven side-by-side weed seed control mills fitted to the rear of his harvester. The mills aim to render weed seed that passes through them unviable for germination.

“I ran those for three seasons, and we were very happy with the mills,” Stewart said. “The life expectancy of the mills was 1400 hours.”

He decided to buy the mills because burning chaff carts was time-consuming and difficult to complete before sowing.

“We found ourselves trying to burn chaff dumps while seeding,” he said.

Fire escapes

Even after plenty of rain had fallen, smoldering chaff dump fires would escape and burn surrounding stubbles.

Stewart said this was not ideal if canola was planned for sowing on non-wetting sands because intense winds could lead to erosion issues and reduce establishment.

Accordingly, he said switching to mills for harvest weed seed control had worked well on all crops.

Generally, he likes to start harvesting canola at 11 per cent moisture and use a grain drier to bring the seed down to the eight per cent moisture receival standard. This is because Esperance and its surroundings have a cool start to the harvest season.

Using the grain drier, Stewart harvests canola before it is ripe and passes green material through the harvester and the mills.

“I have had very few problems with the mills blocking,” he said. “The other good thing with the mills is they can be switched off and all material diverted through the MAV chopper if necessary.”

Clean canola

Stewart said his integrated approach to weed management over the past six years had made his canola crops largely weed-free.

“If the canola crops are clean and have had a robust rate of diquat (Reglone®) there’s no point putting that bulk of material through the mills because you do lose some capacity … enough to slow you down,” he said.

“If our canola is 100 per cent clean, I will switch off the mills and divert the material to the MAV chopper.”

Stewart and his family have also used the mills for wheat and barley crops. They aim to cut the crops as low as possible to put all weed seed escapes through the mills and the chopper.

He does this to help spread the destroyed weed seed and residue across the full width of his 12.19-metre (40-foot) harvester front.

Challenges noted

Since adopting harvest weed seed control six years ago, Stewart has noticed that weeds tend to drop their seeds earlier than in the past.

“I’m having a few problems with brome grass, and I think what we’ve been doing since 1997 has meant we are selecting for early drop weed seeds,” he said.

“If you keep doing the same thing long enough, the weeds find a way around it.”

Accordingly, he plans to grow Roundup Ready® canola anywhere there are weed issues and use robust rates of diquat to target any in-season escapes to glyphosate.

Since upgrading to a John Deere X9 harvester this year, Stewart hopes to test a new model Redekop SCU prototype.

Although yield is king, he aims to select less-bulky barley and wheat varieties to limit the material going through the harvester and the mills.

“There is more chance of weed seeds passing through the mills and being able to germinate if you have a lot of bulk going through the mills,” he said.

More information: Stewart Wallace, stewwall64@gmail.com

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