Global Positioning Systems (GPS) have significantly improved the accuracy and effectiveness of aerial weed control, says West Coast helicopter pilot Kevin Anderson.

He describes the invention of GPS guidance systems as the best technological development since the advent of aerial application itself.

GPS utilises satellite signals to fix the exact position of a vehicle or aircraft. This enables aerial agricultural contractors applying fertiliser or chemical to make precise applications within highly localised areas.

Kevin Anderson, of Hokitika-based Anderson Helicopters, saw the potential of GPS six years ago and was one of the first agricultural helicopter pilots in the country to have a system fitted in his helicopter (a Bell Jet Ranger).

He says it has proved an invaluable tool for topdressing and weed spraying because it eliminates the over-application associated with traditional methods and improves accuracy.

“A few years ago a client asked me to spray what he thought was a 20 hectare block of gorse but when we mapped it out with GPS it turned out to be closer to 40 hectares. If we had treated it as 20 hectares, we risked covering too large an area with an insufficient amount of chemical.

“But once you’ve mapped an area with GPS you know exactly what quantity of chemical is required and can apply it with considerable accuracy.”

Kevin runs Anderson Helicopters with the help of wife Sandra, who does the ground support work, and his son Fletcher (named after the legendary aircraft), a trainee pilot.

The Andersons perform topdressing and weed spraying work for forestry companies, sheep and beef, deer and dairy farmers in the West Coast, Nelson and Canterbury regions.

They have a reputation for good service and this explains why some of their clients have been with them for more than 20 years.

“We never compromise on quality,” says Kevin.

“There is no point in cutting corners because news of a bad job will get back home before you do.”

Gorse and broom spraying is a big part of the business, but the size of each job can vary considerably – from one hectare on a Golden Bay dairy farm to 40 ha on a large sheep and beef station in Canterbury.

Kevin says a typical client will spend between $5000 and $10,000 a year on gorse spraying.

With more than thirty years agricultural flying experience under his belt, he reckons a good weed spraying job hinges on four factors – timing, application, technique and the quality of the chemical.

He says Tordon Brushkiller XT and Grazon are the key herbicides used for gorse and broom control.

“They are very reliable products and the technical support from Dow AgroSciences is first class.

“Both products are grass-safe and that’s important to farmers with established pasture amongst the gorse and broom. They don’t want to see that valuable grass wiped out.”

Kevin says the majority of spraying work takes place between September and February, “but Tordon gives us the flexibility to spray a month either side of that and still get a good kill”.

He says good follow-up control is crucial, particularly in areas like the West Coast and Golden Bay where gorse can grow half a metre a year if left unchecked.

He says the thrust of any aerial campaign should be to “hit weeds hard the first time” so that follow-up control is much easier.