A HI-TECH approach to spraying weeds is saving a Boort spraying contractor and grain grower substantial amounts on his chemical costs.

Last year, Steve Lanyon converted his custom-made boom spray to a WeedSeeker system, which has infra-red sensors mounted on each spray nozzle.

The sensors can detect weeds and other plant material and distinguish between them and material such as bare ground or stubble.

When the sensors sense a weed, they activate the spray nozzle and apply the chemical only when it is needed.

By spraying the target weeds only and not bare ground or stubble for example, far less chemical and water is used.

Steve, who farms about 3500ha at Boort with his wife, Kathryn, and parents Trevor and Karen, first saw the WeedSeeker system demonstrated at the Mallee Machinery Field Days a couple of years ago.

"We thought it looked like a great idea so last year we decided to give it a go," Steve said.

And it did not take him long to see the benefits.

"We started spraying for summer weeds in December and we saved 46 per cent of our usual amount of herbicides on the first pass by using the WeedSeeker," Steve said.

"On the second pass, it was 91 per cent. The 'brew' in the spray was worth about $24 a hectare so the savings are substantial when you multiply that out over 3500ha."

The WeedSeeker system is easy to operate, according to Steve, and the key to the best results is to calibrate the sprayer on an area of the paddock that best represents the ground conditions across the area to be sprayed.

"Having the sensors only 38cm apart, they can see more ground in tall straw," he said.

"You can spray out larger weeds and leave small grasses for the sheep if you like. And you can spray more hectares on each tank so you can use higher water rates and get a better kill on weeds. It's a really good way to kill couch grass with high rates of glyphosate."

Steve said the WeedSeeker was a good spraying tool for controlling weeds in stubble or fallow ground.

"You simply drive the spray boom over the right piece of ground, hit the calibrate button on the control unit in the cabin and then start spraying," he said.

"If it's calibrated correctly, the spray will only be applied to any leafy, green material that the sensors record.

"It provided an excellent summer weed-kill for us and that's really important for conserving moisture and nutrients in years when rainfall is limited."

Grant Yates, director of Southern Precision, which distributes the WeedSeeker system, said the WeedSeeker units on the boom spray had light-emitting diode sensors that produced red and near infra-red light.

"A special detector in the unit can calculate the reflectance and absorption of the light emitted and that varies depending on the chlorophyl levels of the plant," Grant said.

"It pretty much distinguishes between green and not green but you can also tailor the system to distinguish between shades of green, for example, like that of skeleton weed compared with a broadleaf grass.

"You can raise or lower the sensitivity of the system to suit different plants. It will detect weeds down to the size of about a 50-cent piece and you can confidently spray at 15-20km/h ground speed."

It costs about $2000 a sensor installed, or about $5000 a metre of spray boom to fit the WeedSeeker.

Grant said even though it might cost $150,000 to set up the system on a boom spray, the reduction in chemical and water use meant the up-front cost was quickly recouped.

"Our feedback is that the system usually pays for itself in about two years," Grant said.

"But it also has other benefits, for example, the reduction in water use.

"We have found it has become quite popular in vineyards and orchards where water use has to be kept to an absolute minimum."