chemical mowing trial

Otorohanga District Council is ramping up its efforts to eradicate and control yellow bristle grass (YBG).

Roading Manager Andreas Senger says Council has recently started a chemical mowing trial on three local roads affected by YBG.

“We have chosen the roads to trial and are currently working on a strategy with our maintenance contractor and the supplier,” he says.

“We have learnt quite a bit about it and there’s still a bit of work to do but we will be working within budget, continually monitoring the situation and looking at the best options to stunt its growth and keep the seed away.” 

Mr Senger says chemical mowing is the use of chemicals to reduce or prevent growth of grass and weeds so that the need for mechanical mowing is eliminated or reduced.

“Chemical mowing works by spraying suitable weed killer in low dosage on the growth to slow it down without killing it.

“A “scorched earth” policy is not good for the road, as it promotes soil erosion, so growth is good, although unwanted growth needs to be tackled.

“All that is desired is to prevent the growth from forming seeds. This also works on the grasses to lower the need for mowing.

“Chemical mowing has been used all over the world since the 70’s with good success and we want to trial it here to see if it will suit our need to control the spread of YBG.”

Yellow bristle grass is an annual-seeding plant which spreads rapidly, reducing pasture quality.

Its distinctive spiky seed heads begin to appear in late December but are most obvious in January and February.

YBG is unpalatable to farm stock after the seed heads emerge, so animals avoid it which results in under-utilised pasture.

Not currently classified as a plant pest, YBG seeds can be spread by roadside mowers and freshly-chopped maize silage, and once established on the roadside, it can just as quickly spread into farmland.

“YBG proliferates in areas where bare soil was, and it doesn’t like competition,” says Mr Senger.

“Leaving as much growth in place should, over time, replace YBG with beneficial grasses.”

Otorohanga Councillor Roy Johnson says YBG is a difficult weed to control with a small spraying window of time when control is most effective.

“It will be near impossible to spray all the rural roadsides at the perfect time. It therefore is good that Council undertake a trial to attempt control in some places to see what control can be achieved,” he says.

“Many farmers work hard to control the weed in their own paddocks but feel their efforts are less likely to succeed because of the prevalence of YBG on the road side in some places. The reasons that this weed is so hard to control is that it must be sprayed before seed is set, but it is difficult to identify (looks like a summer grass with very red base).”

Mr Johnson says areas to control are best identified and recorded the season before when seeding is visible.

“It is also hard to control because it can have several germinations over the December-April period and only the plants present at the time will be killed. But it is good that Council are doing something to trial control on the road side and around marker pegs.”