Esperance weed burn shows promise

The West Australian

A new weed-burning machine is being tested in the Esperance area to tackle herbicide resistance without using chemicals.

Herbicide resistance is one of the greatest problems continuous-cropping broadacre farmers face.

Precision Agronomics Australia this week trialled a prototype weed-burning machine, which aims to kill small weeds that have been placed in controlled traffic tramlines during harvest.

PAA agronomist Quenten Knight said the twin burners were fuelled by propane gas and reached a temperature of about 400C while travelling at a speed of about 3km/h to 5km/h.

A rig has been developed by PAA employee Nick Ross that can be mounted on the front or rear of tractors.

Mr Knight said weed burning was not a new concept, but focusing it on a narrow swathe of dirt could be appropriate as part of a system for controlled traffic, using tram lines in paddocks.

"Farmers who are using the controlled traffic system are dumping all their weed seeds and chaff on to compacted tram lines at harvest so the weeds are contained in a very hostile environment," Mr Knight said.

"Most of the weed seeds are going to rot or mulch down when the rain gets into those tram lines. But the remaining weed seeds are likely to be quite resistant to multiple herbicide groups.

"If farmers have got a weed problem in those tramlines they are tending to still treat those weeds with herbicides and they are already potentially resistant, so they are going to start selecting for more and more resistant weeds."

Mr Knight said the weed-burning technology would be appropriate for tramline operations, with wheel tracks about 50cm wide.

"A lot of farmers on a 12me controlled traffic system would only be burning effectively one metre in every 12, so it's quite a contained area," he said.

Mr Knight said it was still early days and the time frame to trial the prototype system, just after sowing or emergence, would last between two and three weeks.

The two most important variables being investigated are the travelling speed and optimum weed size to target and the size of the shrouds over the burners.

"We already know that we have better kill rates with smaller weeds," Mr Knight said.

"The propane burners don't burn the weeds right down to the ground.

"The heat is basically boiling the plants and rupturing cells, then they dehydrate over the next few days and die."

The Esperance trials are targeting canola rotations, which Mr Knight believes might be the most ideal crop to apply the technology.

"If you take all the canola plants on those tramlines, the adjoining crop will more than compensate and shade out any other future germinations on those tramlines," Mr Knight said.

"And weed burning is going to be a pretty slow process, so we think farmers are only going to be travelling somewhere between 3mk/h and 5km/h so they are not going to be able to burn a whole program.

"But if you can narrow it down to a certain part of the rotation, canola for example, you are only likely to be burning maybe a quarter or a third or your program every year, which I think is achievable ."

Mr Knight said PAA was hoping to make the machine a commercial reality, but more trials, research and costings will be need to be carried out over the next few years.

He said early feedback from Esperance farmers who had seen the system had been encouraging.

Mr Knight said early indications had shown a good level of weed kill rate - more results will be available when the trials wrap up in a couple of weeks.

"It will be exciting if this technology works," he said.

"I think the basics are right and it will be the first of its kind in Australia for broadacre, particularly farmers that are using controlled traffic systems and chaff decks to drop seeds on to tramlines during harvest."

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