Dealing with a prick of a grass

Along with all the other spring tasks, manager Garrick Guy has about a dozen workers hunting down and spot-spraying clumps of the invasive pest weed Chilean needle grass.

The job takes several weeks and has had to be repeated every spring since the pest was discovered on the farm in 2008.

The infestation pre-dates the setting up of the vineyard, which occupies 80ha of the 120ha farm, on the main road a few kilometres north of Cheviot. Managing Chilean needle grass occupies them on a “day-to-day basis,” Guy says.

He told attendees at a recent Chilean needle grass focus day on the property that among other measures he can only graze lambs on infested paddocks if they are immediately going to the works. This is to avoid any spread to other paddocks, or to other farms, if the lambs were to be sold as store animals.

Guy’s neighbour Charles Wiffen, chairman of the Chilean needle grass pest management liaison committee, said that sending animals to the works “obviously is the most preferred option”.

“We’ve got to stress to farmers and people in these areas that have it on their properties, to be very vigilant. We are trying to strictly control letting stock move around,” he said.

“If you don’t abide by those rules we unfortunately may have to bring stricter rules in. We are relying on people’s honesty and we hope that continues.”

Chilean needle grass is an invasive pasture pest from South America – ironically from Argentina, not Chile. It reduces crop yields, causes animal welfare issues and places restrictions on infested farms, including stock movements and not being able to make and sell hay.

Most infestations are in Hawkes Bay and Marlborough, but Environment Canterbury’s principal resource management advisor biosecurity, Laurence Smith, told the group that North Canterbury is a very susceptible area, with 325ha now infested “that we know of”.

Although disappointed with the small turnout, Smith acknowledged it was a busy time of year for farmers. But ECan could not find all infestations and it is important that farmers come on board, he said.

Farmers tend not to be too concerned about Chilean needle grass until it becomes obvious, but by then it will already be established. It is a “ticking time bomb” that could take 10 years to show itself from one stray seed.

Smith said glyphosate will kill the plants, but not seeds already in the ground. The plants also harbour seeds low-down that become viable even before the seed heads show themselves.

Taskforce herbicide is also used but is non-specific. Smith said good results are obtained by broadcast herbicide followed by turning the ground and sowing lucerne. However, complete eradication is realistically impossible, Smith concedes.

Chilean needle grass is most likely to be found where there is less competition from desirable pasture species, such as dry hard hill country, areas with light soil, heavily grazed pasture and bare ground.

He says the weed is “just another grass” most of the year until the distinctive purple seed heads become visible in November and December. The seeds are dart-like, with a sharp seed head and a long, kinked tail (awn).

Although not prone to windborne spread, they stick to animals, machinery and clothing. They can bore into animals’ flesh, causing suffering and devalued pelts, meat and wool.

A particular feature of the seeds is the way the corkscrew-shaped awns expand and contract with changing moisture levels, repeatedly twisting the barbed heads in both directions to drive them further into pelts and flesh.

ECan is calling on farmers who suspect they may have Chilean needle grass not to try tackling the problem alone, but to immediately report it to authorities.