App focuses on tussock control

• Published date: 28 September 2022

The free app was released last year to help farmers, mainly in the drought-prone grassland areas of Canterbury and Marlborough, with nassella tussock on their properties

Nassella tussock is the only weed to have its own legislation — the Nassella Tussock Act 1946 — and at its worst forced farmers off properties.

Only this year a heavy infestation was found at a Duntroon farm over several hectares.

Decades have been spent getting it to a stable level, and management is expected to be assisted by the app, developed by AgResearch with MBIE funding in an Environment Canterbury partnership.

AgResearch principal scientist Graeme Bourdot said COVID-19 had got in the way of promoting the app, and just recently it had been raised again in Christchurch conferences attended by biosecurity officers.

He said the idea was that they would educate farmers on the value of the app and how to use it, as it was vital that weed control continued.

Modelling showed weed populations could increase to reach previously economically damaging monocultures if they were left uncontrolled, he said.

‘‘There’s a new generation who are now owners of the farms who haven’t seen it as a huge problem because it’s been so well contained because of this historical effort. So some farmers are saying now ‘I only have a few plants on my property — is it worth controlling them when I’ve got all this gorse and broom that are impacting my management?’.

‘‘This app can show someone might have 10 plants per hectare which aren’t causing a loss, but if they left them 40 years out they will see a problem — 10,000 plants per hectare, or whatever, if they haven’t been grubbing, and that will start biting.’’

Dr Bourdot said populations at this level would impact the grazeability of their land and its market value, as no-one would want a nassella-infested farm.

The technology shows farmers what to expect if they stop grubbing nassella or if they improve the efficiency of their grubbing.

Earlier trials estimated a commercial grubbing operation on a typical North Canterbury farm kills on average 34% of the tussocks.

Dr Bourdot said that level of kill would lead to a stable population over time, but farmers could step this up with increased grubbing, and would be able to simulate this in the app to get the expected result.

The app kept track of the seven life stages of the plant. Farmers could use the default grubbing rate of 34% kill across the size classes in the model, or an increased rate over the years ahead...